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This paper presents the methodology for the construction of the KNMI'23 national climate scenarios for the Netherlands. We have developed six scenarios, that cover a substantial part of the uncertainty in CMIP6 projections of future climate change in the region. Different sources of uncertainty are disentangled as much as possible, partly by means of a storyline approach. Uncertainty in future emissions is covered by making scenarios conditional on different SSP scenarios (SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5). For each SSP scenario and time horizon (2050, 2100, 2150), we determine a global warming level based on the median of the constrained estimates of climate sensitivity from IPCC AR6. The remaining climate model uncertainty of the regional climate response at these warming levels is covered by two storylines, which are designed with a focus on the annual and seasonal mean precipitation response (a dry‐trending and wet‐trending variant for each SSP). This choice was motivated by the importance of future water management to society. For users with specific interests we provide means how to account for the impact of the uncertainty in climate sensitivity. Since CMIP6 GCM data do not provide the required spatial detail for impact modeling, we reconstruct the CMIP6 responses by resampling internal variability in a GCM‐RCM initial‐condition ensemble. The resulting climate scenarios form a detailed storyline of plausible future climates in the Netherlands. The data can be used for impact calculations and assessments by stakeholders, and will be used to inform policy making in different sectors of Dutch society. Plain Language Summary: To prepare society for the effects of future climate change, we need to know what the future climate will be like. In this paper we explain the method that is used to construct six different scenarios that describe possible future climates of the Netherlands. The scenarios make assumptions about future greenhouse gas emissions, and are based on the outcomes of climate models that simulate the response of the climate to these emissions. The KNMI'23 climate scenarios show that strongly reducing global emissions strongly reduces the expected changes in the climate of the Netherlands. In the scenario in which global emissions continue to rise until 2080, Dutch society will have to adapt to a much stronger increases in heat and precipitation extremes, increased risks of droughts with low river discharge in summer, and increased risk of flooding due to high river discharges in winter. In the coming years the climate scenario data will be used to evaluate what needs to be done to keep the country a safe place for people to live in and to thrive in, under changing climate conditions. Key Points: We present a methodology for the construction of regional climate scenarios using a storyline approach to partition uncertaintyResults from CMIP6 are reconstructed with a GCM‐RCM initial condition ensemble to produce high‐resolution scenario data for end‐usersSix scenario variants cover emission uncertainty (high, moderate, low) and uncertainty in the regional response (dry‐trending, wet‐trending) [ABSTRACT FROM AUTHOR]

Warming climate and precipitation changes induce notable shifts in climate zones. In this study, the latest generation of global climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and the previous generation CMIP5 under high‐emission scenarios are used together with observations and applied to the Köppen‐Geiger climate classification. The aim is to shed light on how projected warming and changes in precipitation will influence future climate zones and their associated ecosystems while revealing differences between the two model generations. Compared to CMIP5 models, CMIP6 models exhibit slightly improved performance in replicating the observed Köppen‐Geiger map for the historical (1976–2005) period and similar inter‐model agreement for the future. The models show major changes in climate zones with a range of projections depending on which ensemble subset is used: 37.9%–48.1% of the global land area is projected to change climate zone by the end of the century, with the most pronounced changes expected over Europe (71.4%–88.6%) and North America (51.2%–65.8%). CMIP6 models project a higher rate of areal climate zone change (km2/year) throughout the 21st century, which is mainly driven by their greater global land warming rates. Using a likely equilibrium climate sensitivity subset of CMIP6 models that is consistent with the latest evidence constrains the climate zone shifts, and their projections better match the results of CMIP5 simulations. Although the high warming rates of some CMIP6 models are less credible, the risks associated with them are greater, and they heighten the need for urgent action to preserve terrestrial ecosystems. Plain Language Summary: Köppen‐Geiger climate classification is a tool to map regional climate zones based on a region's temperature and precipitation. In recent decades, increasing temperatures and changing precipitation trends have started to affect the distribution of those climate zones, and more extensive changes are expected throughout the 21st century. In this paper, we assess the observed and expected changes in the global distribution of Köppen‐Geiger climate zones using observations along with the latest and the previous generation of global climate model projections. We find that shifts in climate zones are more pronounced in the latest generation of models due to their questionable greater global warming rate projections. Depending on which subset of model projections is used, up to half of the Earth's land area faces the risk of shifting to a different climate zone by the end of the century, with the greatest changes expected in Europe and North America. The rate of change (affected area per year) is also projected to accelerate through the 21st century, suggesting that vulnerable species and agricultural practices might have less time to adapt to changes in climate zones than previously projected. Key Points: Coupled Model Intercomparison Project Phase 6 (CMIP6) exhibits slightly improved performance in simulating the globally observed historical Köppen‐Geiger climate zones compared to CMIP5By the end of the century, 38%–48% of the global land area is projected to be in a different climate zone than todayThe rate of climate zone change is projected to accelerate, with more pronounced rates in CMIP6 due to considerably higher warming rates [ABSTRACT FROM AUTHOR]

The planet is predicted to become drier because of accelerating global warming, increasing great challenges to the survival of terrestrial species. However, the understanding of when and where increasing aridity in the future will lead to abrupt biodiversity loss is still limited. Here, we predicted the spatiotemporal dynamics of future vertebrate biodiversity loss driven by increasing aridity at the assemblage scale under the scenario framework of the shared socio‐economic pathways (SSPs) and representative concentration pathways (RCPs). The results show that, under the high‐emissions scenario of SSP5‐8.5, more than 24.19% of terrestrial assemblages are projected to have at least one vertebrate species exposed to unprecedented aridity conditions by 2100, leading to 55.29% of terrestrial vertebrate species experiencing local habitat loss. In addition, the mean magnitude of global exposure is expected to reach 17.47% by 2100. Within these assemblages, most species will be simultaneously exposed to unprecedented aridity conditions, with an average exposure abruptness of 78.00%, most of which will occur intensively after 2050. If we manage to reduce greenhouse gas emissions to the SSP1‐2.6 (SSP2‐4.5) scenario, the magnitude of exposure can significantly decrease to 7.35% (10.56%), and the onset of exposure can be delayed by 43 (30) years, averaging approximately 30% (14%) of vertebrate species from local habitat loss. Our findings also highlight that the concurrent extremes of increasing aridity and rising temperature in Southeast Asia and Amazon rainforests may amplify exposure risks, which can motivate decision‐makers to respond early and effectively to mitigate abrupt ecological disruption. Plain Language Summary: The global land surface is predicted to become more drier in the future due to the accelerating global warming, which places great challenges on the survival of terrestrial species. In this paper, we predicted the future spatiotemporal dynamics of biodiversity loss of vertebrate species as a result of the increase in aridity, trying to understand when and where the increasing aridity will cause biodiversity loss intensively and lead to abrupt ecological disruption. We found that, under the high‐emissions scenario (∼4.4°C global temperature rise), more than 24.19% of global terrestrial assemblages are projected to have at least one vertebrate species exposed to aridity condition exceeding their niche, leading to the consequence that 55.29% of species will experience habitat loss. The exposure events within most terrestrial assemblages will occur simultaneously after 2050. If we manage to reduce emissions to the low (intermediate)‐emissions scenario (∼1.8°C and 2.7°C global temperature rise), the onset of exposure can be delay by 43 (30) years. Our findings also highlight that the concurrent extremes of increasing aridity and rising temperature in Southeast Asia and Amazon rainforests may amplify exposure risks, which can motivate decision‐makers to respond early to mitigate abrupt ecological disruption. Key Points: We predicted and highlighted the risk of abrupt biodiversity loss in terrestrial vertebrate species driven by increasing aridityMore than 24% of terrestrial assemblages will be exposed to unprecedented aridity, and 55.29% of species will experience local habitat lossConcurrent extremes of increasing aridity and rising temperature in Southeast Asia and Amazon rainforests may amplify exposure risks [ABSTRACT FROM AUTHOR]

The frequency with which tropical cyclones (TCs) occur controls all other aspects of tropical cyclone risk since a storm that does not occur can do no harm. Yet this frequency is poorly understood. There is no accepted theory that explains the average number of TCs that occur each year on the Earth, nor how that number will change with global warming. Arguments based on global budgets of heat or moisture do not yet appear helpful, nor does a detailed understanding of the physical processes of TC genesis. Empirical indices that predict TC frequency as a function of large‐scale environmental variables can explain some of its relative variations in space and time, but not its absolute value. Global numerical models with horizontal grid spacings on the order of 25–50 km have allowed much improved simulations of TC activity, however. Many such models project a decrease in frequency with warming, but some project an increase. Idealized simulations, including those at higher resolutions, offer promise by allowing a systematic, deductive investigation of the roles of individual environmental factors. In addition to the larger‐scale environmental modulation of genesis likelihood, precursor disturbances, or "seeds", may exert an independent influence on TC frequency. Plain Language Summary: The term tropical cyclone frequency refers to the average number of tropical cyclones (also known as hurricanes, typhoons, etc.) which occur each year, either over the earth as a whole or in smaller regions. In this paper, the authors review the state of the science regarding what is known about tropical cyclone frequency. The state of the science is not great. There are around 80 tropical cyclones in a typical year, and we do not know why it is this number and not a much larger or smaller one. We also do not know much about whether this number should increase or decrease as the planet warms‐‐‐thus far, it has not done much of either on the global scale, though there are larger changes in some particular regions. No existing theory predicts tropical cyclone frequency. In this situation, we are left with numerical models as our primary tool, and the authors discuss the strengths, weaknesses, and different ways of using such models to investigate tropical cyclone frequency. Idealized simulations, in which the planet is made simpler than it really is, are allowing some new insights. Another promising avenue of investigation involves studying the weaker disturbances that sometimes strengthen into tropical cyclones. Key Points: We do not understand why the number of tropical cyclones per year is what it is, nor how it may be changingIn the absence of theory, our main tools are numerical modelsPromising research directions include idealized simulations at high resolution and study of precursor disturbances, or "seeds" [ABSTRACT FROM AUTHOR]

Precipitation extremes are increasing globally due to anthropogenic climate change. However, there remains uncertainty regarding impacts upon flood occurrence and subsequent population exposure. Here, we quantify changes in population exposure to flood hazard across the contiguous United States. We combine simulations from a climate model large ensemble and a high‐resolution hydrodynamic flood model—allowing us to directly assess changes across a wide range of extreme precipitation magnitudes and accumulation timescales. We report a mean increase in the 100‐year precipitation event of ~20% (magnitude) and >200% (frequency) in a high warming scenario, yielding a ~30–127% increase in population exposure. We further find a nonlinear increase for the most intense precipitation events—suggesting accelerating societal impacts from historically rare or unprecedented precipitation events in the 21st century. Plain Language Summary: Heavy rainfall is increasing globally due to human‐caused global warming. However, it is still unclear how these increases in heavy rainfall might affect flood risk. In this paper, we investigate how global warming and population changes together may be affecting the number of people at risk from floods in the United States. We combine simulations from a climate model and flood model—allowing us to consider a wide range of heavy rainfall events. We report a ~20% increase in the size and a >200% increase in the frequency of very heavy and rare rainfall events, which leads to a ~30–127% increase in the number of people at risk from floods. Finally, we find that the heaviest rainfall events increase by the widest margin—suggesting the possibility of major increases in damage and disruption caused by severe floods in the 21st century. Key Points: Population exposure to flood hazard is increasing due to both climate‐driven increases in extreme rainfall as well as demographic shiftsThere is a wide range of plausible increases in population exposed to flood hazard, depending strongly on climate and growth scenarioWe find a nonlinear increase for most extreme events, suggesting accelerating societal impacts from historically unprecedented rainfall [ABSTRACT FROM AUTHOR]

The climate is an aggregate of the mean and variability of a range of meteorological variables, notably temperature (T) and precipitation (P). While the impacts of an increase in global mean surface temperature (GMST) are commonly quantified through changes in regional means and extreme value distributions, a concurrent shift in the shapes of the distributions of daily T and P is arguably equally important. Here, we employ a 30‐member ensemble of coupled climate model simulations (CESM1 LENS) to consistently quantify the changes of regionally and seasonally resolved probability density functions of daily T and P as function of GMST. Focusing on aggregate regions covering both populated and rural zones, we identify large regional and seasonal diversity in the probability density functions and quantify where CESM1 projects the most noticeable changes compared to the preindustrial era. As global temperature increases, Europe and the United States are projected to see a rapid reduction in wintertime cold days, and East Asia to experience a strong increase in intense summertime precipitation. Southern Africa may see a shift to a more intrinsically variable climate but with little change in mean properties. The sensitivities of Arctic and African intrinsic variability to GMST are found to be particularly high. Our results highlight the need to further quantify future changes to daily temperature and precipitation distributions as an integral part of preparing for the societal and ecological impacts of climate change and show how large ensemble simulations can be a useful tool for such research. Plain Language Summary: The weather varies naturally from day to day and between regions, seasons, and years. Ecosystems and our society are both adapted to the average weather conditions of a given place and to how variable the temperature and rainfall amounts are around that average. As the global surface temperature changes, whether through natural cycles or human interference, so may this variability. In this paper, we investigate changes to the distributions of daily temperature and rainfall for different levels of surface temperature increase. By using a large set of simulations from the same climate model, we estimate their means and shapes, currently and in the near future. We find that in parts of Europe and the United States, wintertime cold days will disappear more rapidly with global warming than hot days increase, leading to a less variable climate state. In Africa and the Arctic, however, climate conditions will rapidly transition out of the range of preindustrial variability and into a climate state not yet experienced by modern society. We emphasize that in order to prepare for the impacts of climate change, we need information about changes to average properties and to extreme events and about the potential changes to daily variability itself. Key Points: Daily temperature and precipitation distributions from CESM1 Large Ensemble are shown to be functions of region, season, and surface temperatureLarge differences are found in regional distributions, where they are particularly sensitive to surface temperature anomalyWe identify regions where global warming may rapidly shift seasonal climate away from preindustrial conditions [ABSTRACT FROM AUTHOR]

Risk of climate‐related impacts results from the interaction of climate‐related hazards (including hazardous events and trends) with the vulnerability and exposure of human and natural systems. Despite the commitment of the Paris Agreement, the integrate research on climate change risk combining risk‐causing factors and risk‐bearing bodies, the regional differences in climate impacts are still missing. In this paper we provide a quantitative assessment of hazards and socioeconomic risks of extreme events, risks of risk‐bearing bodies in China under global warming of 1.5 and 2.0 °C based on future climate scenarios, and quantitative evaluation theory for climate change risk. For severe heat waves, hazards might significantly intensify. Affected population under 2.0 °C warming might increase by more than 60% compared to that of 1.5 °C. Hazards of severe droughts and floods might strengthen under Representative Concentration Pathway 8.5 scenario. Economic losses might double between warming levels of 1.5 and 2.0 °C, and the population affected by severe floods might continuously increase. Under the integrate effects of multiple disasters, the regions with high population and economic risks would be concentrated in eastern China. The scope would gradually expand to the west with socioeconomic development and intensification of extreme events. High ecological risks might be concentrated in the southern regions of the Yangtze River Basin, while the ecological risk in northern China would expand. High agriculture yield risks might be distributed mainly in south of the North China Plain, the Sichuan Basin, south of the Yangtze River, and west of Northwest China, and the risk levels might continuously increase. Plain Language Summary.: Based on the climate and socioeconomic scenario data from the Inter‐Sectoral Impact Model Inter‐comparison Project and International Institute for Applied Systems Analysis, risks from climate change were identified under different warming levels, considering socioeconomic damage and ecosystem and food production losses. The relatively developed areas of eastern China exhibit high risks, and the risks show a westward and northward expansion trend. Socioeconomic damage, natural ecosystem, and food production losses would increase with socioeconomic development and intensification of global warming. We believe that a quantitative assessment of climate change risk should integrate climate‐related hazards with the vulnerability and exposure of human and natural systems. These results can provide decision‐making support for governments and a database for adapting to climate change. Key Points: Risks of socioeconomic development, ecosystem and food production would increase between 1.5 °C and 2.0 °C warming, economic losses might doubleIncreases in annual socioeconomic losses of 2.0 °C warming would be more significant than those of 1.5 °CEastern China exhibits high integrate risks of climate change, which present westward and northward trends from 1.5 °C to 2.0 °C warming [ABSTRACT FROM AUTHOR]

Climate change induces significant changes in storm characteristics, particularly for short‐duration extreme storms (heavy rain features), impacting their intensity and spatio‐temporal distribution. Although alterations in precipitation intensity are well documented, past studies examining changes in spatio‐temporal distribution of storms (storm rainrates) were region‐specific and focused on isolated aspects of change in space or time, eluding a comprehensive understanding of the precise nature and extent of these changes. Bridging this gap, this study introduces a novel grid‐based measure of storm homogeneity, "spatio‐temporal homogeneity" metric and investigates the global patterns of change in combined spatio‐temporal characteristics of extreme storms. Analyzing the 30 min × 0.1° × 0.1° resolution Global Precipitation Measurements, the study finds that extreme storms are shrinking in both space and time due to rising surface air temperatures, predominantly in tropics. In contrast, temperate regions experience expanded extreme storms with increasing temperatures. The study also identifies a global trend toward more front‐loading in storms with rising temperatures, driven by a substantial increase in tropics and southern temperate regions. Conversely, storms in northern temperate regions become slightly more rear‐loaded as temperature increases. Furthermore, the study finds that characteristics of short–duration storms (6–12 hr) are more sensitive to temperature changes. Overall, this study contributes valuable insights into the global spatio‐temporal changes of extreme storms, highlighting regions most susceptible to alterations in storm patterns due to climate change. These findings are essential for developing effective adaptation strategies and flood management practices to cope with the changing nature of extreme storms in a warming climate. Plain Language Summary: Extreme rainfall can lead to floods, affect ecosystems, and challenge water management. How intense the rain is, how wide an area it covers, and how long it lasts are key factors in determining flood risk. Additionally, whether the rainfall starts strong and tapers off (front‐loaded) or begins gently and then fades quickly (rear‐loaded)—also plays a role. As the climate changes, it's crucial to understand how these extreme storm characteristics are evolving to better prepare for the future. This study introduces a new way to measure changes in the size and duration of extreme storms in response to rising temperatures worldwide. It also examines whether warmer temperatures make storms more likely to start strong and taper off or the opposite. The findings show that in tropical regions, extreme storms are becoming effectively shorter and covering effectively smaller areas as temperatures increase. Conversely, in temperate regions, storms are lasting longer and covering effectively larger areas. Additionally, storms in areas below 30°N are tending toward more front‐loading, while those above 30°N are becoming more rear‐loaded. This research helps us understand how warming temperatures are changing storm patterns and can inform better flood preparedness and water management strategies. Key Points: Introduces Spatio‐Temporal Homogeneity metric to effectively track comprehensive changes in storm characteristics across both space and timeRising temperature causes "spatio‐temporally peakier" storms in tropics, intense precipitation burst in smaller area over shorter durationRising temperature leads to more front‐loading in storms, notably in tropics and southern temperate regions, increasing flash flood risk [ABSTRACT FROM AUTHOR]

Observations and climate projections suggest a larger increase in tropical cyclone (TC)‐induced rainfall than that can be explained by the Clausius‐Clapeyron relationship of 7% increase in vapor content for each 1°C degree rise in temperature. However, these studies using diverse data sources and methods over various periods show inconsistencies regarding the location of this increase ‐ whether in the TC inner core or outer regions ‐ and offer differing explanations for the reported trends. This study uses the Pseudo‐global warming methodology on simulations of 117 western North Pacific TCs making landfall in Southeast Asia to investigate changes in TC rainfall structure by the end of the century under the SSP2‐4.5 and SSP3‐7.0 scenarios. Specifically, it tests the sensitivity of changing trends to various analysis methods used in previous studies and identifies the underlying physical mechanisms driving these changes. The findings indicate an amplified increase in rainfall in the TC inner core across all future scenarios, along with potentially decreased rainfall in the outer region under certain future climate conditions. Among TC categories, Supertyphoons exhibit the most significant increased rainfall across future states. Changes in TC primary and secondary circulations, TC structure, and the convergence of heat and moisture are the main factors shaping future rainfall patterns, outweighing the effects of changes in atmospheric and convective stability. Plain Language Summary: Tropical cyclone (TC)‐related rainfall is increasing with global warming. Typically, a 1°C increase in temperature leads to about a 7% increase in the atmosphere's water vapor holding capacity. However, the rise in TC rainfall outpaces this rate. Observations indicate this enhanced increase occurs in the TC outer region due to greater environmental moisture. Contrarily, modeling future projections suggest this concentrates in the inner core due to intensified TCs. This study analyzes a large data set of 819 simulations from 117 TCs making landfall in Southeast Asia to capture changes in future rainfall patterns under two contemporary climate change scenarios. Our findings reveal that the enhanced increase occurs in the TC inner core in all future states, while rainfall in the outer region decreases under specific climate conditions. Supertyphoons generate the heaviest rainfall, with minimal variations observed across climate scenarios. Variations of all dynamic and thermodynamic factors closely tied to TC rainfall are investigated to provide a comprehensive picture of the physics behind the changes. The interplay between TC dynamics (e.g., primary and secondary circulations), TC structure, and thermodynamic conditions (e.g., convergence of moisture, and temperatures), plays a critical role in the changing behaviors of TC rainfall. Key Points: Rainfall increases in the cyclone's inner core across all future states but decreases in the outer region under specific statesVariations in cyclone circulations, structure, convergence of moisture and heat in future climates drive rainfall changing patternsSupertyphoons cause the heaviest rainfall compared to other categories, with slight variations noted across climate conditions [ABSTRACT FROM AUTHOR]

In the Paris Agreement countries have agreed to act together to hold global warming well below 2°C over preindustrial levels and to pursue efforts to limit warming to 1.5°C. To assess if the world is on track to meet this long‐term temperature goal, countries' pledged emissions reductions (Nationally Determined Contributions, NDCs) need to be analyzed for their implied warming. Several research groups and nongovernmental organizations have estimated this warming and arrived at very different results but have invariably concluded that the current pledges are inadequate to hold warming below 2°C, let alone 1.5°C. In this paper we analyze different methods to estimate 2100 global mean temperature rise implied by countries' NDCs, which often only specify commitments until 2030. We present different methods to extend near‐term emissions pathways that have been developed by the authors or used by different research groups and nongovernmental organizations to estimate 21st century warming consequences of Paris Agreement commitments. The abilities of these methods to project both low and high warming scenarios in line with the scenario literature is assessed. We find that the simpler methods are not suitable for temperature projections while more complex methods can produce results consistent with the energy and economic scenario literature. We further find that some methods can have a strong high or low temperature bias depending on parameter choices. The choice of methods to evaluate the consistency of aggregated NDC commitments is very important for reviewing progress toward the Paris Agreement's long‐term temperature goal. Key Points: Several methods to project 2100 temperature rise from countries' climate commitments are introduced and analyzedSimple methods can neither reproduce the scenario literature nor assess if emissions reduction pledges are 2°C consistentScenario database‐based methods can reproduce literature ranges and be suitable for the assessment of Paris Agreement commitments [ABSTRACT FROM AUTHOR]

Abstract: At the 21st session of the United Nations Framework Convention on Climate Change Conference of the Parties (COP21) in Paris, an agreement to strengthen the effort to limit the global temperature increase well below 2°C was decided. However, even if global warming is limited, some regions might still be substantially affected by climate change, especially for continents like Africa where the socio‐economic conditions are strongly linked to the climatic conditions. In the paper we will discuss the analysis of indices assigned to the sectors health, agriculture, and infrastructure in a 1.5, 2, and 3°C global warming world for the African continent. For this analysis an ensemble of 10 different general circulation model‐regional climate model simulations conducted in the framework of the COordinated Downscaling EXperiment for Africa was investigated. The results show that the African continent, in particular the regions between 15°S and 15°N, has to expect an increase in hot nights and longer and more frequent heat waves even if the global temperature will be kept below 2°C. These effects intensify if the global mean temperature will exceed the 2°C threshold. Moreover, the daily rainfall intensity is expected to increase toward higher global warming scenarios and will affect especially the African Sub‐Saharan coastal regions. [ABSTRACT FROM AUTHOR]

Global warming exacerbates the increase of soil moisture drought by accelerating the water cycle, posing potential threats to food security and ecological sustainability. The design of drought prevention and mitigation policies should be based on the reliable detection of the future change signal in droughts, so it is critical to know when the signal can be detected (Time of Emergence, ToE) in the background noise of the climate system. While the ToE framework has been successfully applied for temperature‐related signal detection, the ToE for changes in drought has not been well studied. Based on 66 Coupled Model Intercomparison Project Phase 6 model ensemble members under four Shared Socio‐economic Pathways, we conduct a global ToE analysis of seasonal soil moisture drought characteristics and discuss the impact of different warming levels. Six subregions with robust increase in soil moisture droughts are identified. For drought frequency, most of the subregion's ToE is centered around 2080, however for drought intensity it is much earlier and can even reach around 2040 in AMZ. For drought frequency and drought intensity, approximately 14%–22% and 47%–49% of global land areas would reach ToE in 21st century. The global land areas with ToE of increasing droughts would increase by at least 1/5 when global warming level is kept to 2°C rather than 1.5°C above pre‐industrial conditions. This suggests that limiting global warming can significantly delay the emergence time of increases in seasonal soil moisture droughts, allowing additional adaptation time for the drought‐related sectors. Plain Language Summary: Global warming has increased the frequency of droughts, especially soil moisture droughts with widespread impacts. Thus, when would the soil moisture drought change exceed the noise of the climate system and signal "emerge" (Time of Emergence, ToE) has far‐reaching implication for relevant government departments and stakeholders to make corresponding adaptations. In this work, the future changes in seasonal soil moisture droughts are projected by using Coupled Model Intercomparison Project Phase 6 (CMIP6, multi‐model simulations of historical and future climate) data under four possible future development scenarios (named Shared Socio‐economic Pathways), and the effects of controlling global warming levels on the ToE of droughts are discussed. Results show that the frequency of seasonal soil moisture droughts would increase over 42%–48% of global land areas in the future, and 14%–22% of global land areas would show detectable signals of increased drought frequency before 2100. If the global warming level is controlled within 2°C rather than 1.5°C, the areas with ToE would increase by at least one fifth, except for drought intensity under the scenario of the most energy‐saving and emission reduction. This work highlights the risk of rapid emergence of robust soil moisture drought increases under climate change. Key Points: The timing of detectable future changes in seasonal soil moisture droughts are identified through the time of emergence frameworkDetectable increase signals in drought frequency and intensity are predicted in 14%–22% and 47%–49% of land areas by the end of this centuryThe areas of detectable signals for drought characteristics would increase by 1/5 when limiting warming within 2°C compared to 1.5°C [ABSTRACT FROM AUTHOR]

Recent years were characterized by spatially co‐occurring hot and wet extremes around the globe, raising questions about the contribution of human‐induced global warming to the changing likelihoods of such extreme years. To characterize spatially co‐occurring extremes we investigate recent trends in global and regional land area that is concurrently affected by hot or wet annual maxima taking observational uncertainty into account. Observed trends in the land area affected by extreme events are assessed in the context of Earth System Model (ESM) simulations for present‐day and early‐industrial climate conditions in a detection and attribution setting. We compare different reanalysis and station‐based observational products to account for observational data uncertainty. At the global scale, trends of spatially co‐occurring hot or wet annual maxima in all observational products can be explained by ESM simulations driven by historical radiative forcing that accounts for human‐induced changes in the composition of the atmosphere but cannot be explained by ESM simulations that account for an early‐industrial radiative forcing. At the regional scale, trends in spatially co‐occurring hot annual maxima are in general coherent among observational products and can in most cases be attributed to human influence on the climate system. Trends in spatially co‐occurring wet annual maxima show differences in some regions, highlighting the importance of a multi‐dataset approach to overcome observational product dependencies. Despite observational uncertainty, we find robust detection and attribution results for many regions. These results can complement previous assessments on regional exposure to hot and wet events from the new IPCC AR6 report. Plain Language Summary: Recent years were characterized by spatially co‐occurring hot and wet extremes around the globe, leading to questions about the contribution of human‐induced climate change to the occurrence of such extreme years. In this study, we investigate trends in the global and regional land area that is concurrently affected by hot or wet annual maxima. Due to observational uncertainties, we investigate different observation‐based data products for temperature and rainfall. By comparing observational trends in the land area affected by extreme events to respective trends from Earth System Model ensemble simulations accounting for climate conditions of the past decades and early‐industrial climate conditions, we can evaluate their attribution to human‐induced climate change. On the global scale, observed trends of spatially co‐occurring hot or wet annual maxima cannot be simulated by climate models when considering early‐industrial climate conditions, but are captured by climate models considering recent climate conditions. This holds also true for the detection and attribution of regional trends in concurrent land area affected by hot annual maxima. Observational products agree in many regions on the detection and attribution of regional trends in concurrent land area affected by wet annual maxima, but also disagree in some regions. Key Points: Global and regional trends of spatially concurrent hot or wet annual maxima can be attributed to human‐induced climate changeIn some regions observational products show inconsistencies in the sign of detectable trends in concurrent wet annual maximaLarge regional differences in spatial exposure and steady increase in concurrent land area affected by hot or wet annual maxima is detected [ABSTRACT FROM AUTHOR]

Stratospheric Aerosol Injection (SAI) is a proposed method of climate intervention aiming to reduce the impacts of human‐induced global warming by reflecting a portion of incoming solar radiation. Many studies have demonstrated that SAI would successfully reduce global‐mean surface air temperatures; however the vast array of model scenarios and strategies result in a diverse range of climate impacts. Here we compare two SAI strategies—a quasi‐ equatorial injection and a multi‐latitude off‐equatorial injection—simulated with the UK Earth System Model (UKESM1), both aiming to reduce the global‐mean surface temperature from that of a high‐end emissions scenario to that of a moderate emissions scenario. We compare changes in the surface and stratospheric climate under each strategy to determine how the climate response depends on the injection location. In agreement with previous studies, an equatorial injection results in a tropospheric overcooling in the tropics and a residual warming in the polar regions, with substantial changes to stratospheric temperatures, water vapor and circulation. Previous comparisons of equatorial versus off‐equatorial injection strategies are limited to two studies using different versions of the Community Earth System Model. Our study evaluates how the climate responds in UKESM1 under these injection strategies. Our results are broadly consistent with previous findings, concluding that an off‐equatorial injection strategy can minimize regional surface temperature and precipitation changes relative to the target. We also present more in‐depth analysis of the associated changes in Hadley Circulation and regional temperature changes, and call for a new series of inter‐model SAI comparisons using an off‐equatorial strategy. Plain Language Summary: Stratospheric Aerosol Injection (SAI) is a method to tackle the impacts of global warming and involves reflecting some of the sun's rays away from Earth. Different strategies for implementing SAI can have various effects on the climate. This study compares two strategies—one injecting at the equator and the other at different latitudes. Both strategies successfully lower global temperatures, but they also lead to different regional climate changes. The equatorial strategy cools the tropics too much and doesn't cool the poles enough. Whereas the off‐equatorial strategy minimizes some of the negative impacts seen in the equatorial strategy. In summary, injecting aerosols away from the equator avoids unfavorable climate impacts. Key Points: We compare the climate impacts of equatorial and multi‐latitude Stratospheric Aerosol Injection (SAI) strategies under the Geoengineering Model Intercomparison Project G6 frameworkWe demonstrate that an off‐equatorial multi‐latitude injection strategy minimizes unfavorable climate impactsThis research highlights the importance of injection location in determining the impacts of SAI on the climate [ABSTRACT FROM AUTHOR]

Stratospheric Aerosol Geoengineering (SAG) is proposed to offset global warming; however, the use of this approach can an impact on the hydrological cycle. We used simulations from Coupled Model Intercomparison Project (CMIP5) and Geoengineering Model Intercomparison Project (G3 simulation) to analyze the impacts of SAG on precipitation (P) and to determine its responsible causes in West Africa and Sahel region. CMIP5 historical data were first validated, the results obtained are consistent with observational data. Under the Representative Concentration Pathway scenario RCP4.5, a slight increase is found in the West Africa Region relative to present‐day climate. The dynamic processes especially, the monsoon shifts are responsible for this precipitation change. Under RCP4.5, during the monsoon period, reductions in P are 0.86%, 0.80% relative to the present‐day climate in the Northern and Southern Sahel, respectively, while precipitation is increased by 1.04% in the West African Region. Under SAG, we find a 3.71% decrease of precipitation in the West African Region while the precipitation decrease is 17.4% and 8.47% respectively in the North Sahel and South Sahel. This decrease in monsoon precipitation is mainly explained by changes in dynamics, which lead to weakened monsoon circulation and a shift in the distribution of monsoon precipitation. This result suggests that SAG deployment to balance all warming can be harmful to rainfall in WAR if the amount of SO2 to be injected into this tropical area is not taken into consideration. Plain Language Summary: Stratospheric Aerosol Geoengineering (SAG) deployment has been proposed to reduce temperature increase in the context of global warming but its impacts on the hydrological cycle and the underlying causes need to be evaluated on the regional scale. While some effects of Stratospheric Aerosol Geoengineering on the water cycle are uncertain, various studies suggest that there could be considerable changes in regional rainfall. Climate simulations (Coupled Model Intercomparison Project: CMIP5 and Geoengineering Model Intercomparison Project: GeoMIP) are used in this work to quantify the impacts on the monsoon rainfall in West Africa. We determine the changes in precipitation and the mechanisms responsible for these changes in West Africa during summer using Stratospheric Aerosol Geoengineering. Under global warming, while a slight decrease of precipitation is noted in the Sahel region, a significant decrease in rainfall is obtained over the West Africa region and the Sahel region under SAG. The main processes responsible for the changes of precipitation under SAG are determined based on the decomposition approach. Results show that changes in precipitation are largely related to changes in dynamic processes (monsoon circulation). Key Points: We determine the changes of West African Summer Monsoon precipitation using stratospheric aerosol geoengineering injections climate modelsIncrease of precipitation is presented under global warming while its decrease is obtained with stratospheric aerosol geoengineering modelsThese changes of West African Summer Monsoon precipitation are mainly driven by the dynamic processes [ABSTRACT FROM AUTHOR]

During and after recent La Niña events, the decline of the eastern East African (EA) March‐April‐May (MAM) rains has set the stage for life‐threatening sequential October‐November‐December (OND) and MAM droughts. The MAM 2022 drought was the driest on record, preceded by three poor rainy seasons, and followed by widespread starvation. Connecting these dry seasons is an interaction between La Niña and climate change. This interaction provides important opportunities for long‐lead prediction and proactive disaster risk management, but needs exploration. Here, for the first time, we use observations, reanalyses, and climate change simulations to show that post‐1997 OND La Niña events are robust precursors of: (a) strong MAM "Western V sea surface temperature Gradients" in the Pacific, which (b) help produce large increases in moisture convergence and atmospheric heating near Indonesia, which in turn produce (c) regional shifts in moisture transports and vertical velocities, which (d) help explain the increased frequency of dry EA MAM rainy seasons. We also show that, at 20‐year time scales, increases in atmospheric heating in the Indo‐Pacific Warm Pool region are attributable to warming Western V SST, which is in turn largely attributable to climate change. As energy builds up in the oceans and atmosphere, during and after La Niña events, we see stronger heating and heat convergence over warm tropical waters near Indonesia. The result of this causal chain is that increased Warm Pool atmospheric heating and moisture convergence sets the stage for dangerous sequential droughts in EA. These factors link EA drying to a stronger Walker Circulation and explain the predictable risks associated with recent La Niña events. Plain Language Summary: In 2022, an unprecedented sequence of five sequential failed rainy seasons, exacerbated by high global food and fuel prices, drove an exceptional food security crisis in Ethiopia, Somalia, and Kenya, pushing more than 20 million people into extreme hunger. The potential for famine loomed in some areas. Beginning in late 2020, this was the longest and most severe drought recorded in the Horn of Africa in at least 70 years, resulting in multiple failed harvests and large‐scale livestock deaths that decimated the food and income sources of rural communities. It placed increasing pressure on the cost of food among urban communities and led to rising levels of destitution and displacement. These droughts occurred against the backdrop of the "East Africa Climate Paradox", which centers on the discrepancy between climate change model projections of increased East African March–April–May rains, and many observational studies pointing toward declines. Before the western Pacific Ocean warmed dramatically in 1998, the link between La Niña events and dry March‐April‐May (MAM) rains was weak. Since 1998, the link has been very strong. This set the stage for dangerous sequential droughts in October‐November‐December and MAM, such as in 2010/11, 2016/17, 2020/21, and 2021/22. Here, we link the decline to an important question: Why are so many recent La Niña events associated with dry March–April–May rains? La Niña events tend to reach their maximum intensity in the boreal fall and winter, often producing East African droughts during the October‐November‐December "short rains". We explain the link between La Niña and dry MAM seasons using observations, reanalyses, and the latest (Phase 6) climate change simulations. While climate change models do not recreate the observed East African drying, they recreate the observed west Pacific warming very well. Climate change, not natural decadal variability associated with the Pacific Decadal Oscillation, has increased west Pacific sea surface temperatures. This, in turn, is increasing the "Western V Gradient", a measure of the east‐west differences in Pacific Ocean temperatures. When this gradient is negative, there are frequent East African droughts, and this happens in a predictable way during or after recent La Niña events. This allows us to predict many dry rainy seasons approximately 8 months in advance. Such predictive capacity is important, because the frequency of strong Pacific temperature gradients is increasing. We show that climate change simulations recreate this tendency for stronger Pacific SST gradients, and project that it will continue over the coming decades. What connects East African droughts to Pacific temperature gradients? We answer this question by examining observed atmospheric heating, moisture transports, and moisture convergence patterns. In general, eastern East Africa is dry because it resides along the western edge of the Indian Ocean branch of the Indo‐Pacific "Walker Circulation". Across eastern East Africa and the western Indian Ocean, and over the central and eastern Pacific, rainfall and moisture levels are low. In the area around Indonesia (the eastern Indian and western Pacific Oceans), winds drive moisture convergence and heavy rains. Here, building on many years of research by scientists working for the Famine Early Warning Systems Network, we show for the first time that the strength of the Walker Circulation can be quantified using atmospheric heating and moisture convergence. Since 1998, when there has been a La Niña in October–November–December, there has almost always been strong March‐April‐May heating and moisture convergence around Indonesia, and suppressed rainfall in eastern East Africa. Climate change‐enhanced La Niñas amplify the Pacific trade winds which produce strong March–April–May sea surface temperature gradients. These gradients amplify the Walker Circulation, and reduce moisture convergence and ascending atmospheric motions over the eastern Horn of Africa. We conclude with a look toward the future evolution of the Walker Circulation by relating the observed strength of the Walker Circulation to 20‐year averages of western and eastern Pacific sea surface temperatures. Both play a significant role, and together explain 96% of the observed variability. The observed Walker Circulation intensification is primarily driven by the west Pacific, which in turn is strongly related to climate change. CMIP6 projections of Pacific sea surface temperatures, combined with the observed empirical relationships, imply further strong increases in Walker Circulation intensities. Hence, additional rainfall declines appear likely, especially during or directly following La Niña events. More optimistically, the process‐based analyses presented here suggest that many of the dry seasons may be predictable at long lead times, based on Pacific sea surface temperature gradients. Key Points: Human‐induced warming in the Western V region of the Pacific, combined with La Niña, has produced frequent, predictable March‐April‐May droughtsThermodynamic analyses link these droughts to a stronger Walker Circulation driven by predictable warming in the Western V regionProjected CMIP6 SST increases imply a tendency for continued Walker Circulation intensification and associated drought risks in eastern East Africa [ABSTRACT FROM AUTHOR]

In the coming decades, coastal flooding will become more frequent due to sea‐level rise and potential changes in storms. To produce global storm surge projections from 1950 to 2050, we force the Global Tide and Surge Model with a ∼25‐km resolution climate model ensemble from the Coupled Model Intercomparison Project Phase 6 High Resolution Model Intercomparison Project (HighResMIP). This is the first time that such a high‐resolution ensemble is used to assess changes in future storm surges across the globe. We validate the present epoch (1985–2014) against the ERA5 climate reanalysis, which shows a good overall agreement. However, there is a clear spatial bias with generally a positive bias in coastal areas along semi‐enclosed seas and negative bias in equatorial regions. Comparing the future epoch (2021–2050) against the historical epoch (1951–1980), we project ensemble‐median changes up to 0.1 (or 20%) in the 1 in 10‐year storm surge levels. These changes are not uniform across the globe with decreases along the coast of Mediterranean and northern Africa and southern Australia and increases along the south coast of Australia and Alaska. There are also increases along (parts) of the coasts of northern Caribbean, eastern Africa, China and the Korean peninsula, but with less agreement among the HighResMIP ensemble. Information resulting from this study can be used to inform broad‐scale assessment of coastal impacts under future climate change. Plain Language Summary: In the next few decades, coastal flooding is expected to become more frequent due to rising sea levels and changes in storms. To understand and prepare for these changes, we use a global hydrodynamic and multiple climate models to investigate how storm surges (a temporarily rise in water level during a storm) will respond to a warmer climate. These are the first global projections of storm surges based on highly detailed climate models (25–50 km). We compare the model output for recent years (1985–2014) with real‐world weather data, known as reanalysis data, and find a good overall agreement. However, the comparison also shows relatively large differences with larger or smaller values in certain areas. For the future (2021–2050), results show storm surge changes up to 20%. These changes vary around the world. Some areas (Mediterranean, northern Africa, and southern Australia) might experience lower storm surges, whereas other areas (South Australia, Alaska, the northern Caribbean, eastern Africa, China, and the Korean Peninsula) might experience higher storm surges. By using advanced computer models as done here, we are able to better understand how climate change could impact coastal area and thus make informed decisions for the future. Key Points: Storm surge projections from 1950 to 2050 based on the Global Tide and Surge Model and a ∼25 km‐resolution High Resolution Model Intercomparison Project climate model ensembleValidation against ERA5 reanalysis (1985–2014) shows that the model performs well globally, but also reveals a clear spatial biasThe median‐ensemble change of the 1 in 10‐year storm surge levels from 2021–2050 compared to 1951–1980 shows changes up to 0.1 m or 20% [ABSTRACT FROM AUTHOR]

In contrast to the "wet gets wetter and dry gets drier" paradigm, here, using observations and climate model simulations, we show that the mean rainfall over the semi‐arid northwest parts of India and Pakistan has increased by 10%–50% during 1901–2015 and is expected to increase by 50%–200% under moderate greenhouse gas (GHG) scenarios. The GHG forcing primarily drives the westward expansion of the Indian summer monsoon rainfall (ISMR) and is facilitated by a westward expansion of the Indian Ocean (IO) warm pool. Mechanistically, the westward expansion of ISMR is a consequence of the episodic genesis over IO and the northward propagation of an expanded Inter‐Tropical Convergence Zone on a sub‐seasonal time scale. While an adaptation strategy to increased hydrological disasters is a must, harnessing the augmented rainfall would lead to a substantial boost in food productivity, bringing transformative changes in the socio‐economic condition of people in the region. Plain Language Summary: An apparent eastward shift of the Indian monsoon has led to the arid conditions in the west and north‐west regions of India where monsoon was once active, and the Indus Valley civilizations thrived (5,300–3,300‐year BP). A reversal of the process and a westward expansion of the present‐day Indian monsoon would transform the west and north‐west India to a humid "monsoonal" climate and provide food security to the expanding population of the country. The present study shows that the Indian monsoon is indeed expanding to the west with 10% decrease of mean rainfall in the northeast and 25% increase in the west and north‐west during the historical period with a potential of 50%–100% increase in the north‐west under SSP2–4.5. Harvesting the increased rainfall has the potential for significant increase in food productivity bringing in transformative changes in the socio‐economic condition of people of the region. Key Points: Global warming could potentially cause a westward expansion of the Indian monsoonRainfall in northwest India and Pakistan has increased and will continue to rise due to greenhouse gasesIncreased monsoon rainfall can improve food productivity and socio‐economic conditions in the region [ABSTRACT FROM AUTHOR]

Enhanced rock weathering (ERW) on croplands has emerged as an economically and ecologically promising negative emissions technology. However, estimated total carbon sequestration potential from ERW on croplands and its potential sensitivity to climate conditions requires further understanding. Here we combine 1‐D reactive transport modeling with climate model experiments to simulate ERW on ∼1,000 agricultural sites globally. Applying a fixed rate of 10 tons of basalt dust per hectare on these sites sequesters 64 gigatons of CO2 over a 75‐year period; when extrapolated to all agricultural land, ERW sequesters 217 gigatons of CO2 over the same time interval. However, we find that a significant fraction of applied basalt does not weather even on a multidecadal timescale, indicating the need to optimize application strategies for cost effectiveness. We find that ERW becomes modestly more effective with global warming and predict that the payback period for a given ERW deployment is significantly shorter in hot and humid environments currently coinciding with relatively low per‐capita incomes. These results provide strong impetus for investment in agricultural reform in developing economies and highlight an additional potential co‐benefit of ERW. Plain Language Summary: Enhanced rock weathering (ERW) on croplands is a promising negative emissions concept that accelerates natural weathering by amending soils with crushed rock. Our simulations of ERW with a fixed rate of 10 tons of basalt dust per hectare on all global croplands suggest ERW can sequester >200 gigatons of CO2 over a 75‐year period. This suggests that cost and logistical concerns, rather than weathering potential, are likely to be the key limiting factors for large‐scale deployment of enhanced weathering. Notably, ERW is resilient to global climate change and becomes more effective with global warming. ERW is moreover far more efficient in hot and humid environments currently coinciding with relatively low per‐capita gross domestic product economies. Our study provides strong support for the assertion that ERW represents a resilient carbon capture strategy that is non‐competitive for arable land and can foster CO2 removal at the gigaton scale. Key Points: Enhanced rock weathering (ERW) with fixed annual application rates of 10 tons of basalt dust per hectare on 1,000 global cropland sites sequesters 64 gigatons of CO2 over 2006–2080Extrapolated to all croplands, ERW with a fixed application rate of 10 tons of basalt dust per hectare sequesters 215 gigatons of CO2 over 2006–2080ERW is resilient to global climate change but is much more efficient over hot and humid environments [ABSTRACT FROM AUTHOR]

The sudden swings between drought/heat and pluvial could cause adverse impacts far surpassing the sum of their individual effect. We propose a concept of intraseasonal "compound whiplash event" (CWE) to investigate sudden swings between wet and the compounding warm‐dry events and their changes under climate change. We find that global warming would likely escalate the compound whiplash frequency to two to three and half times (two to three times) by the end of the 21st century under the business‐as‐usual scenario (mitigated scenario). The growing threat of CWE not only stems from the increasing occurrence but also from its intensified severity and extended spatial coverage. Among all sub‐regions, East Asian summer monsoon (EASM) region would expect the largest intensification. The resulting population exposure would soar two‐to‐three‐fold over Asia. Populous regions such as North India and EASM region might face a much worse situation than the western China where population is sparse and projected to decline. Moreover, the seasonality of swings with opposite directions would further split as a response to the skewed Asian monsoon annual cycle, leading to more frequent heat‐drought to pluvial swings in spring, and more opposite‐direction swings in autumn, disrupting cultivation and water management convention. Plain Language Summary: Either drought/heat or pluvial already causes adverse impacts on ecosystem and human society. The swing between these extremes could escalate their impact to the next level, far beyond their simple addition. Though some studies have investigated weather whiplash on longer time scales, such as months to years, intraseasonal whiplashes on an event basis are rarely explored. Hence, we propose a concept of "compound whiplash event" to investigate the intraseasonal alternation between warm‐dry and wet conditions and their potential changes in a warmer future climate. We find that global warming not only leads to one‐to‐two and half times more compound weather whiplashes by the end of 21st century under the business‐as‐usual scenario, but also intensifies their severity and extends their extent. Within Asia, East Asian summer monsoon region will likely face the largest increase. As a result, the population exposed to the compound weather whiplash would double or even triple, especially in the populous regions with further population growth. In addition, with skewed Asian monsoon annual cycle, the seasonality of swings expects a coherent shift, that is, more heat‐drought swings in spring and more opposite‐direction swings in autumn, potentially posing more disruption in agricultural and water management activities. Key Points: Intraseasonal compound weather whiplash in Asia is introduced and defined using a 3D event‐based approachCompound weather whiplash is projected to triple with intensified severity and shifted seasonality by the end of the 21st centurySouthern and eastern Asia will see the most increase in population exposure while population decline tempers the increase elsewhere [ABSTRACT FROM AUTHOR]

Continued climate warming is reducing seasonal snowpacks in the western United States, where >50% of historical water supplies were snowmelt‐derived. In the Upper Colorado River Basin, declining snow water equivalent (SWE) and altered surface water input (SWI, rainfall and snowmelt available to enter the soil) timing and magnitude affect streamflow generation and water availability. To adapt effectively to future conditions, we need to understand current spatiotemporal distributions of SWE and SWI and how they may change in future decades. We developed 100‐m SnowModel simulations for water years 2001–2013 and two scenarios: control (CTL) and pseudo‐global‐warming (PGW). The PGW fraction of precipitation falling as snow was lower relative to CTL, except for November–April at high elevations. PGW peak SWE was lower for low (−45%) and mid elevations (−14%), while the date of peak SWE was uniformly earlier in the year for all elevations (17–23 days). Currently unmonitored high elevation snow represented a greater fraction of total PGW SWE. PGW peak daily SWI was higher for all elevations (30%–42%), while the dates of SWI peaks and centroids were earlier in the year for all elevations under PGW. PGW displayed elevated winter SWI, lower summer SWI, and changes in spring SWI timing were elevation‐dependent. Although PGW peak SWI was elevated and earlier compared to CTL, SWI was more evenly distributed throughout the year for PGW. These simulated shifts in the timing and magnitude of SWE and SWI have broad implications for water management in dry, snow‐dominated regions. Plain Language Summary: Snowpack water storage has historically functioned as a reliable extension of manmade reservoir storage. Loss of this storage has consequences for water resource management, ecological communities, and natural hazards including wildfire. We modeled snow accumulation and melt at high spatial resolution in the Upper Colorado River Basin to assess patterns in the timing and magnitude of snow storage and snowmelt for historical and future scenarios. We analyze these patterns in relation to existing snow monitoring station coverage, and ask how this coverage may need to change in future decades to better represent water availability. Our results indicate widespread future snow storage losses at lower elevations, but limited change at higher elevations that will likely remain conducive to seasonal snow accumulation and melt for decades to come. Peak snow storage and peak snowmelt occurred earlier for all elevations in future years, with increased peak surface water input noted at all elevations. A greater fraction of future snow storage will be in currently unmonitored high elevations. Projected elevation dependent changes from this study have implications for other dry, snow dominated regions, and additional work is needed to evaluate combined effects of widespread snow loss and earlier, flashier input on coordinated water management. Key Points: Projections show lower peak snow water equivalent (SWE) below 3,000 m and earlier peak SWE, peak surface water input (SWI) at all elevationsGreater future peak SWI and reduced annual snow‐derived SWI for all elevations, with a more even SWI distribution throughout the yearA greater fraction of future SWE will be in high elevations that are currently unmonitored [ABSTRACT FROM AUTHOR]

Compound dry and hot events (CDHEs) have increased significantly and caused agricultural losses and adverse impacts on human health. It is thus critical to investigate changes in CDHEs and population exposure in responding to climate change. Based on the simulations of the Coupled Model Intercomparison Project Phase 6 (CMIP6), future changes in CDHEs and population exposure are estimated under four Shared Socioeconomic Pathways climate scenarios (SSPs) at first. And then the driving forces behind these changes are analyzed and discussed. The results show that the occurrence of CDHEs is expected to increase by larger magnitudes by the end of the 21st century (the 2080s) than that by the mid‐21st century (2050s). Correspondingly, population exposure to CDHEs is expected to increase significantly responding to higher global warming (SSP3‐7.0 and SSP5‐8.5) but is limited to a relatively low level under the modest emission scenarios (SSP1‐2.6). Globally, compared to 1985–2014, the exposure is expected to increase by 8.5 and 7.7 times under SSP3‐7.0 and SSP5‐8.5 scenarios by the 2080s, respectively. Regionally, Sahara has the largest increase in population exposure to CDHEs, followed by the Mediterranean, Northeast America, Central America, Africa, and Central Asia. The contribution of climate change to the increase of exposure is about 75% by the 2080s under the SSP5‐8.5 scenarios, while that of population change is much lower. The conclusion highlights the importance and urgency of implementing mitigation strategies to alleviate the influence of CDHEs on human society. Plain Language Summary: Under global warming, the occurrence of compound dry and hot events (CDHEs) is expected to increase, which may cause more severe damage to human society. Based on the Coupled Model Intercomparison Project Phase 6, the changes in population exposure to CDHEs and the driving forces are estimated and discussed in this study. The results show that the occurrence of CDHEs and population exposure are expected to increase substantially, especially under high‐emission scenarios. Sahara is expected to have the largest increase in population exposure to CDHEs, followed by the Mediterranean, Northeast America, Central America, Africa, and Central Asia. The influence of climate change on the increase in exposure is much larger than that of the population change. Therefore, it is important and urgent to make mitigation strategies to alleviate the impacts of CDHEs on human society. Key Points: The occurrence of summertime compound dry and hot events is projected to increase substantially over the 21st century across the globeExposure is expected to increase significantly under SSP3‐7.0 and SSP5‐8.5 but is limited to a low level under SSP1‐2.6 scenariosClimate change determines the increase in population exposure in most regions of the world [ABSTRACT FROM AUTHOR]

Today, climate change is affecting virtually all terrestrial and nearshore settings. This commentary discusses the challenges of measuring climate‐driven physical landscape responses to modern global warming: short and incomplete data records, land use and seismicity masking climatic effects, biases in data availability and resolution, and signal attenuation in sedimentary systems. We identify opportunities to learn from historical and paleo data, select especially sensitive study sites, and report null results to better characterize the extent and nuances of climate‐change effects. We then discuss efforts to improve attribution practices, which will lead to better predictive capabilities. We encourage the Earth‐science community to prioritize scientific research on climate‐driven physical landscape changes so that societies will be better prepared to manage the effects on health and safety, infrastructure, water–food–energy security, economics, and ecosystems that follow from climate‐driven physical landscape change. Plain Language Summary: Modern global warming will ultimately affect physical landscape processes virtually everywhere on Earth, and some of those effects are evident already. This commentary describes the challenges to measuring climate‐driven physical landscape responses to global warming: short and incomplete data records, land use and earthquakes masking climatic effects, biases in data availability and resolution, and climate signals becoming harder to read at the downstream end of a landscape. We discuss ways to collect more informative data in key locations to better understand climate‐change impacts, while also diligently reporting where impacts are not evident. Forming a more complete picture in these ways will mean societies are better prepared to predict and manage impacts on human health and safety, infrastructure, water–food–energy security, economics, and ecosystems that are linked to climate‐driven physical landscape change. Key Points: Modern anthropogenic climate change affects a vast range of geomorphic settingsWe identify challenges of measuring physical landscape response to modern climate change and opportunities to improve studiesBetter understanding physical landscape impacts will prepare societies to manage hazards and economic effects of climate change [ABSTRACT FROM AUTHOR]

Millions of lakes from around the world freeze during winter. These frozen surfaces provide essential ecosystem services that are vital to many northern communities. However, the availability of safe lake ice that is oftentimes required to support these services is under threat from climate change. Here we use a 100‐member ensemble of climate model simulations to investigate changes in the presence of safe lake ice for different recreation and provisioning activities across the Northern Hemisphere. Our projections suggest that the duration of safe ice for recreational purposes will shorten, on average, by 13, 17, and 24 days within a 1.5°C, 2°C, and 3°C warmer world (relative to 1900–1929), respectively. The projected change in the duration of safe ice will be greater in higher latitudes, but with the most densely populated lower‐latitude regions experiencing the greatest percent change. The use of lake ice to support critical transportation infrastructure will also be influenced by future warming through the loss of thicker ice this century. However, our projections suggest that the magnitude of change in the duration of safe ice will differ depending on the ice thickness requirements. For transportation that requires the thickest ice cover, the number of days with safe ice will decline by 90%, 95%, and 99% with 1.5°C, 2°C, and 3°C global warming, respectively. We highlight the need for the development and implementation of adaptation plans to address the imminent loss of critical wintertime transportation infrastructure across the Northern Hemisphere. Key Points: The availability of safe lake ice for recreation will decrease, on average, by 13 and 24 days in response to a global warming of 1.5°C and 3°CThe most densely populated regions across the Northern Hemisphere are projected to experience the greatest percent loss of safe lake iceWithout human intervention, the duration of safe ice for winter ice roads is projected to decline by up to 99% within a 3°C warmer world [ABSTRACT FROM AUTHOR]

The temperature of a well‐mixed ice‐water mixture stays constant until the ice melts due to external heat. Whether the temperature over the Arctic Ocean exhibits an analogous stagewise evolution to reach an ice‐free point remains unclear. Therefore, this study explored the characteristics of extratropical climate change before and after a period during which the Arctic Ocean was ice‐free in summer using multimodel simulations. Here, we show that the seasonality of Arctic warming varies between the two periods separated by an ice‐free summer. The warming maximum in the cold season delayed for a month after becoming ice‐free than before. In addition, the warming maximum lagged behind the sea‐ice decline maximum before becoming ice‐free, whereas the maximums of the two became coordinated after becoming ice‐free. The closed cross‐season energy cycle demonstrated that the capacitor effect of the Arctic Ocean with delayed release of the energy taken up in spring and summer due to sea‐ice decline and seawater absorption is crucial for the seasonality observed in Arctic climate change. Moreover, we found that although Arctic amplification induced general weakening in high‐frequency weather variability in the mid‐high latitudes via decreased meridional temperature gradients, significant weakening was induced only after becoming ice‐free under high emission. Our findings suggest that the two stages of Arctic sea‐ice decline should be taken into consideration when dealing with global warming. Plain Language Summary: Taking the classic stagewise temperature evolution of ice‐water mixtures into consideration (Figure S1 in Supporting Information S1), this study investigated climate change in the Arctic before and after an ice‐free summer using multimodel simulations. Our results showed that the seasonality characteristics of Arctic warming varied between these two periods. The capacitor effect (charging and discharging in the warm and cold seasons, respectively) of the cross‐season energy cycle associated with sea‐ice decline on Arctic warming was observed. Moreover, our findings indicated that variability in the weather decreased in mid‐high latitudes due to Arctic amplification‐induced southward cold airflow from the Arctic not being as cold as before. This research highlights the importance of stagewise decline of Arctic sea‐ice. Key Points: Seasonality of Arctic warming will change after ice‐free relative to that before, under both the intermediate and high future emissionsCapacitor effect of the Arctic Ocean due to cross‐season energy cycle is crucial for seasonality in Arctic climate changeArctic amplification induces a decrease in weather variability in mid‐high latitudes, especially after ice‐free under high emission [ABSTRACT FROM AUTHOR]

Earth System Models' complex land components simulate a patchwork of increases and decreases in surface water availability when driven by projected future climate changes. Yet, commonly‐used simple theories for surface water availability, such as the Aridity Index (P/E0) and Palmer Drought Severity Index (PDSI), obtain severe, globally dominant drying when driven by those same climate changes, leading to disagreement among published studies. In this work, we use a common modeling framework to show that Earth System Model (ESM) simulated runoff‐ratio and soil‐moisture responses become much more consistent with the P/E0 and PDSI responses when several previously known factors that the latter do not account for are cut out of the simulations. This reconciles the disagreement and makes the full ESM responses more understandable. For ESM runoff ratio, the most important factor causing the more positive global response compared to P/E0 is the concentration of precipitation in time with greenhouse warming. For ESM soil moisture, the most important factor causing the more positive global response compared to PDSI is the effect of increasing carbon dioxide on plant physiology, which also drives most of the spatial variation in the runoff ratio enhancement. The effect of increasing vapor‐pressure deficit on plant physiology is a key secondary factor for both. Future work will assess the utility of both the ESMs and the simple indices for understanding observed, historical trends. Plain Language Summary: Rivers and groundwater provide almost all water used by humans, and soil moisture is critical for vegetation and crops worldwide. Supercomputer model simulations of rivers, groundwater and soil moisture under future global warming routinely project that some world regions will experience increases in the availability of these resources, while others will experience decreases. Yet the simple formulas that scientists have traditionally relied on to measure climatic "drought" and "aridity" obtain large future decreases in water availability (drying) almost everywhere. This has led to confusion in prior studies and reports. In this study, we resolve this apparent paradox by pinpointing exactly why the supercomputer simulations are less pessimistic than the simple formulas. For rivers and groundwater, the most important reason is that precipitation gets "flashier" and more intense with global warming. For soil moisture, the most important reason is that increasing carbon dioxide allows vegetation to use less water, keeping more water in the soil. Both of these processes are included in the computer models, but not in the simple formulas. This new understanding gives us greater confidence that the computer models are behaving reasonably. Key Points: Community Land Model 5 runoff ratio and soil moisture responses to climate change closely follow the Aridity Index (P/E0) and Palmer Drought Severity Index (PDSI) in a simplified simulationRunoff ratio increases much more than P/E0 in full simulations primarily due to changes in the temporal pattern of precipitationSoil moisture increases more than PDSI in full simulations primarily due to CO2 and vapor pressure deficit effects on plant physiology [ABSTRACT FROM AUTHOR]

Understanding the response of extreme precipitation (EP) at a city scale to global warming is critical to reducing the respective risk of urban flooding. Yet, current knowledge on this issue is limited. Here, focusing on an urban agglomeration in the tropics, Singapore, we reveal that future global warming enhances both frequency and intensity of EP, based on simulations with a state‐of‐the‐art convection‐permitting regional climate model. EP intensification can reach maximum "super" Clausius‐Clapeyron rate (≥ $\ge $+7% per K warming) rate, implying a "new normal" of "extreme events get more extreme," which is consistently for both Representative Concentration Pathways 8.5 and 4.5. The intensification is lower for moderate and light precipitation. Also, global warming was found to dampen the urban effect on EP events. The EP enhancement is attributed to the increased atmospheric moisture and convective inhibition due to enhanced low‐level stratification that delays a convection to develop until it becomes more intense. Plain Language Summary: Understanding the response of extreme precipitation (EP) at a city scale to global warming is critical to reducing the respective risk of urban flooding. Here we show that future global warming will enhance both frequency and intensity of EP, based on simulations with a state‐of‐the‐art convection‐permitting regional climate model for an urban agglomeration in the tropics, Singapore. EP is estimated to intensify much more than moderate and light precipitation, implying a "new normal" of "the extreme events get more extreme." Also, global warming was found to dampen the urban effect on EP events. The EP enhancement is attributed to the increased atmospheric moisture and convective inhibition due to enhanced low‐level stratification that delays a convection to develop until it becomes more intense. Key Points: New normal of "extreme events get more extreme" in future city‐scale precipitation is revealedGlobal warming could modify and even reduce the urban footprint on extreme precipitation (EP) eventsThe intensification of EP can reach the maximum at the "super" Clausius‐Clapeyron (≥ $\ge $+7% per K warming) rate [ABSTRACT FROM AUTHOR]

It sounds straightforward. As the Earth warms due to the increased concentration of greenhouse gases in the atmosphere, global temperatures rise and so heatwaves become warmer as well. This means that a fixed temperature threshold is passed more often: the probability of extreme heat increases. However, land use changes, vegetation change, irrigation, air pollution, and other changes also drive local and regional trends in heatwaves. Sometimes they enhance heatwave intensity, but they can also counteract the effects of climate change, and in some regions, the mechanisms that impact on trends in heatwaves have not yet been fully identified. Climate models simulate heatwaves and the increased intensity and probability of extreme heat reasonably well on large scales. However, changes in annual daily maximum temperatures do not follow global warming over some regions, including the Eastern United States and parts of Asia, reflecting the influence of local drivers as well as natural variability. Also, temperature variability is unrealistic in many models, and can fail standard quality checks. Therefore, reliable attribution and projection of change in heatwaves remain a major scientific challenge in many regions, particularly where the moisture budget is not well simulated, and where land surface changes, changes in short‐lived forcers, and soil moisture interactions are important. Plain Language Summary: Heatwaves are arguably the most deadly weather phenomena. As the Earth warms due to higher concentrations of greenhouse gases, one would expect heatwaves to become worse as well, killing even more people unless they are better protected against the heat. However, it turns out that the world is not so simple and that many other factors also influence heatwaves. Land use changes, irrigation, air pollution, and other changes also drive trends in heatwaves. Some of these cause much larger trends while some have counteracted the climate change‐driven trends up to now. In some regions, the causes of high trends have not yet been identified. Current generation climate models often do not simulate all these mechanisms correctly so will have to be improved before we can more confidently trust their description of past trends and projections of future trends in heatwaves. Key Points: The IPCC AR6 WG1 states the "frequency and intensity of hot extremes have increased"The IPCC notes that the effect of increased greenhouse gas on high temperatures is moderated or amplified at local scales by other factorsConfident quantitative attribution statements of the human influence on heatwaves are limited by our understanding of these local processes [ABSTRACT FROM AUTHOR]

Tropical Pacific Islands face unknown rates of future warming due to increased greenhouse gas emissions, but almost certain changing climate stresses. Continued global warming is projected to cause further changes to the mean conditions and variability of sea surface temperature (SST), rainfall, and sea surface height (SSH). Previous climate model simulations showed that the equatorial Pacific is likely to have greater increased rainfall, compared to elsewhere in the tropics. There is less certainty about future rainfall changes away from the equator, including around many of the numerous tropical Pacific Islands. Here, we assess the Coupled Model Intercomparison Project‐phase 6 (CMIP6) as it relates to future changes of SST, rainfall, and SSH in the tropical Pacific. Focus is on the island regions of Hawaii, Guam, and American Samoa, as well as the Niño 3.4 region. We consider two development narratives of the 21st century by assessing the SSP2‐4.5 and SSP5‐8.5 experiments, and describe climate changes in the tropical Pacific relative to the recent historical conditions that are likely for either 1.5°C or 3°C of global mean surface temperature (GMST) warming above preindustrial levels. Consistent with prior‐generation climate models, we find that future rainfall increases the most where SST warming is greatest, and also an overall increase of interannual variability associated with the El Niño‐Southern Oscillation (ENSO) affecting rainfall and SSH. We describe changes in SST, rainfall, and SSH for particular warming amounts, and make comparisons with time‐based climate assessments during the 21st century, which are relevant results toward better understanding uncertainty and supporting adaptation efforts in the tropical Pacific Islands. Plain Language Summary: We assess 21st century projected climate changes in the tropical Pacific using the latest generation of climate models that simulate Earth's response to increasing greenhouse gas emissions. Focus is on describing likely changes of rainfall, as well as sea surface temperature and height, for broad regions around Hawaii, Guam, American Samoa, and the other US‐affiliated Pacific Islands. Although it remains unknown how much global warming will occur, the climate models are unequivocal that the tropical Pacific Ocean will continue to warm this century. We constrain this uncertainty by quantifying climate changes for particular warming amounts, such as 1.5°C or 3°C of global warming relative to preindustrial conditions. The surface of both the Earth and the tropical Pacific, specifically, have already warmed by more than 0.5°C. However, it is unknown when the 1.5°C or 3°C global warming amounts will occur. Some uncertainty also remains about regional climate changes associated with the future warming, such as for rainfall around Hawaii and American Samoa, whereas there is more consensus among models about the future rainfall increasing near the equator as well as near Guam in the north‐western Pacific. Increasing equatorial rainfall is a consequence of that region projected to warm fastest and also suggests likely increasing climate variability affecting most tropical Pacific Islands. Key Points: CMIP6 projects increasing 21st‐century rainfall for the equatorial Pacific, and in a broad part of the tropical north‐western PacificRainfall changes are more uncertain for regions around many tropical Pacific Islands, such as Hawaii and American SamoaAssessing seasonal and interannual variability changes for particular warming amounts constrains uncertainty related to the global warming rate [ABSTRACT FROM AUTHOR]

Meteorological to hydrological drought propagation has been widely studied to reflect the relationship between these drought categories and better understand drought mechanisms. However, global warming may alter the drought propagation features, which are not fully understood. This study aims to investigate changes in meteorological and hydrological drought conditions, especially their propagation features in 1.5–3.0°C warmer climates for 8,655 watersheds globally. First, the three‐month scale standardized precipitation index and the standardized runoff index are calculated based on the precipitation simulated by the 15 global climate models and the runoff simulated by the four hydrological models, respectively. Drought events are then identified using the run theory, followed by the calculation of drought propagation features (i.e., pooling, lag, and lengthening) for matched meteorological and hydrological droughts. As a result, both meteorological and hydrological drought conditions (i.e., duration and severity) would relieve in warmer climates due to increased precipitation for regions excluding Western North America, South America, the Mediterranean, Southern Africa, East Asia, and Australia. However, the drought conditions would be more severe during drought propagation from meteorological to hydrological droughts over most regions. During drought propagation, the worsening drought conditions over half of the regions would be more serious first and then relieved with the rising temperature. These results indicate that efforts to slow down global warming can suppress the deterioration of drought conditions in the propagation. Plain Language Summary: Droughts can be categorized into meteorological, hydrological, agricultural, and socioeconomic types from different impacted aspects. Investigating meteorological to hydrological drought propagation can reflect the relationship between these two drought categories to understand the drought mechanism better. However, it is not fully understood whether global warming would alter the drought propagation features or not. Therefore, we evaluated the change of meteorological and hydrological drought conditions, especially their propagation features in 1.5 to 3.0°C warmer climates for 8,655 watersheds around the world. Here we show that both meteorological and hydrological drought conditions would relieve in warmer climates due to the increase of precipitation for regions excluding Western North America, South America, the Mediterranean, Southern Africa, East Asia, and Australia. However, the drought conditions would be more severe during drought propagation over most regions in warmer climates. Our findings promote a better understanding of drought propagation changes under global warming. Key Points: Both meteorological and hydrological drought conditions are projected to relieve in warmer climates for around half of global regionsThe duration and severity developing from meteorological to hydrological droughts would be more severe over most regionsThe worsening duration and severity during the propagation over half of the regions would intensify first and then ease in warmer climates [ABSTRACT FROM AUTHOR]

The hydrological characteristics of a river, including the magnitude and timing of high and low flows, are important determinants of its ecological functioning. Climate change will alter these characteristics, triggering ecological changes in river ecosystems. This study assesses risks of ecological change in 321 major river basins across the globe due to global warming relative to pre-industrial conditions of 1.0, 1.5, 2.0 and 3.0°C. Risks associated with climate-driven changes to high and low flows, relative to baseline (1980-2010; 0.6°C warming), are investigated using simulations from nine global hydrological models forced with climate projections from five global climate models, resulting in an ensemble of 14,445 baseline-scenario members for each warming scenario (9 × 5 × 321). At the globalscale, the likelihood of high risks of significant ecological change in both high and low flows increase with global warming: across all basins there is a medium-high risk of change in high (low) flows in 21.4% (22.4%) of ensemble members for 1.0°C warming, increasing to 61.5% (63.2%) for 3.0°C. Risks are particularly pronounced for low flows at 3.0°C for many rivers in South America, southern Africa, Australia, southern Europe and central and eastern USA. Results suggest that boreal regions are least likely to see significant ecological change due to modified river flows but this may be partly the result of the exclusion of processes such as permafrost dynamics from most global hydrological models. The study highlights the ecological fragility and spatial heterogeneity of the risks that unmitigated climate change poses to global river ecosystems. [ABSTRACT FROM AUTHOR]

Abstract. Risk of climate‐related impacts results from the interaction of climate‐related hazards (including hazardous events and trends) with the vulnerability and exposure of human and natural systems. Despite the commitment of the Paris Agreement, the integrate research on climate change risk combining risk‐causing factors and risk‐bearing bodies, the regional differences in climate impacts are still missing. In this paper we provide a quantitative assessment of hazards and socioeconomic risks of extreme events, risks of risk‐bearing bodies in China under global warming of 1.5 and 2.0 °C based on future climate scenarios, and quantitative evaluation theory for climate change risk. For severe heat waves, hazards might significantly intensify. Affected population under 2.0 °C warming might increase by more than 60% compared to that of 1.5 °C. Hazards of severe droughts and floods might strengthen under Representative Concentration Pathway 8.5 scenario. Economic losses might double between warming levels of 1.5 and 2.0 °C, and the population affected by severe floods might continuously increase. Under the integrate effects of multiple disasters, the regions with high population and economic risks would be concentrated in eastern China. The scope would gradually expand to the west with socioeconomic development and intensification of extreme events. High ecological risks might be concentrated in the southern regions of the Yangtze River Basin, while the ecological risk in northern China would expand. High agriculture yield risks might be distributed mainly in south of the North China Plain, the Sichuan Basin, south of the Yangtze River, and west of Northwest China, and the risk levels might continuously increase.

Responses of summer precipitation in China to global 1.5°C warming with transient and stabilized pathways are investigated through the analysis of the Common Earth System Model climate simulations. Precipitation increases more significantly in southeast China in the stabilized scenario compared with the transient one. The difference is primarily attributable to dynamic factors related to circulation changes and driven by differences of land‐ocean thermal contrast between the two scenarios. The stabilized warming favors conditions of larger ocean warming and smaller land warming, leads to enhanced meridional temperature gradient and ultimately speeds up the jet stream over East Asia. Ageostrophic wind at the entrance of the accelerated jet strengthens ascending motion and precipitation along the coast of Asia from southeast China to India. The enhanced heating over India further induces a Kelvin‐wave response with an anomalous anticyclone that contributes to the enhanced westward shifted of the western North Pacific Subtropical High. Southerly winds at the west flank of the anticyclone transport moisture northward from tropical oceans, and strengthen precipitation in southeast China. Plain Language Summary: This study deals with the issue of regional precipitation response to 1.5°C global warming in accordance to the Paris Agreement on Climate Change for two different pathways, either transient or stabilized. Compared with the transient warming scenario, summer precipitation increases more significantly in southeast China in the stabilized one. This feature of distinctive precipitation responses, with strong implications for policy making in terms of regional climate mitigation and adaptation, is furthermore explored through a moisture budget analysis. Dynamic effect in relation to changes of atmospheric circulation is found to be the major contributor to the difference. The cause of the significant difference in precipitation in South China is attributed to changes of land‐ocean thermal contrast, leading to a series of atmospheric circulation adjustments. Results presented here satisfactorily addressed, for the first time, the long‐standing issue on global warming, namely, how the atmosphere responds distinctively under the transient and stabilized anthropogenic forcing pathways which show however an identical global warming level. Key Points: The summer precipitation increases more significantly in southeast China in the stabilized warming scenario compared with the transient oneThe dynamic effect in relation to changes of atmospheric circulation constitutes the major factor of distinctive precipitation responsesThe differential meridional thermal gradient related to a contrasted land‐ocean warming leads to dynamic changes [ABSTRACT FROM AUTHOR]

Producing enough food to feed a growing population is a great future challenge, especially for vulnerable areas in Africa. There is limited understanding of food security under future climate conditions, particularly under the warming target stipulated in the Paris Agreement. Maize is the most widely cultivated crop in Africa. Taking maize as an example, we present an integrated assessment of maize supply and demand under 1.5°C and 2.0°C warming scenarios, considering the combined impacts of climate change, technology development and population increase. We find that global warming of 1.5°C or 2.0°C would shorten maize growth duration, aggravate droughts, and consequently reduce yield with a spatially explicit pattern. Maize yield would decrease more under global warming of 2.0°C versus 1.5°C. Benefit of rising CO2 concentration could not fully offset the yield loss due to climate change under global warming of 1.5°C. Technology development can significantly improve the ratio of maize supply to demand, which is however subject to future projections on population and technology development. Under a reasonable logarithmic technology development scenario, maize security would become worse in most of the countries in Africa. Our findings highlight the importance of technology development and adaptation strategies to meet the challenges of food security in the vulnerable regions. Key Points: Maize yield would decrease more under 2.0 than 1.5°C warming scenarioUnder a reasonable logarithmic technology development scenario, maize security would become worse in most of the countries in AfricaTechnology development and adaptation strategies are essential to meet the challenges of food security in the vulnerable regions [ABSTRACT FROM AUTHOR]

The extent and impact of climate‐related extreme events depend on the underlying meteorological, hydrological, or climatological drivers as well as on human factors such as land use or population density. Here we quantify the pure effect of historical and future climate change on the exposure of land and population to extreme climate impact events using an unprecedentedly large ensemble of harmonized climate impact simulations from the Inter‐Sectoral Impact Model Intercomparison Project phase 2b. Our results indicate that global warming has already more than doubled both the global land area and the global population annually exposed to all six categories of extreme events considered: river floods, tropical cyclones, crop failure, wildfires, droughts, and heatwaves. Global warming of 2°C relative to preindustrial conditions is projected to lead to a more than fivefold increase in cross‐category aggregate exposure globally. Changes in exposure are unevenly distributed, with tropical and subtropical regions facing larger increases than higher latitudes. The largest increases in overall exposure are projected for the population of South Asia. Plain Language Summary: Global warming changes the frequency, intensity, and spatial distribution of extreme events. We analyze computer simulations of river floods, tropical cyclones, crop failure, wildfires, droughts, and heatwaves under past, present‐day, and potential future climate conditions. Our results show that global warming increases the number of people around the world that are affected by these events each year, both for all event types combined and each type individually. Changes in the chance of being affected by extreme events are unevenly distributed in space. Particularly large increases are simulated for tropical and subtropical regions. Key Points: We quantify the pure effect of climate change on the exposure to extreme climate impact events, for both historical and future time periodsGlobal warming increases the global population exposure to river floods, tropical cyclones, crop failure, wildfires, droughts, and heatwavesThe largest increases in exposure are projected for tropical and subtropical regions [ABSTRACT FROM AUTHOR]

Changes in hydrological cycle under 1.5°C and 2.0°C warming are of great concern on the post‐Paris Agreement agenda. In particular, the annual range of precipitation, that is, the difference between the wet and dry seasons, is important to society and ecosystem. This study examines the changes in precipitation annual range using the Community Earth System Model low‐warming (CESM‐LW) experiment, designed to assess climate change at stabilized 1.5°C and 2.0°C warming levels. To reflect the exact annual range in different regions, wet and dry seasons are defined for each grid point and year. Based on this metric, the precipitation annual range would increase by 3.90% (5.27%) under 1.5°C (2.0°C) warming. The additional 0.5°C of warming would increase annual range of precipitation by 1.37%. The enhancement is seen globally, except in some regions around the subtropics. Under the additional 0.5°C of warming, a significant increase in the annual range occurs over 15% (22%) of the ocean (land) regions. The increase is associated with the enhanced precipitation during wet season. Moisture budget analysis shows that the enhancement in annual range is dominated by vertical moisture advection, which includes thermodynamic (TH, moisture) and climate dynamic (CD, circulation changes) terms. The TH term plays a dominant role, while the CD term partly offsets the effects of the TH term. The TH term dominates over most regions except for part of the tropical ocean and some of the land regions, where the CD term is also remarkable. Thus, the enhancement of the annual range of precipitation is mainly caused by the increase in moisture. Plain Language Summary: The Paris Agreement proposed a target to limit global warming to less than 2°C and pursue efforts to limit warming to less than 1.5°C. Since then, great effort has been devoted to exploring the impacts of the 1.5°C and 2.0°C warming scenarios. The changes in the seasonal cycles of precipitation have important impacts on natural and human systems but are unknown under 1.5°C and 2°C warming levels. We focus on the changes in the annual range of precipitation, which represents seasonal cycle and is defined as the difference between wet and dry seasonal rainfall in which the wet and dry seasons vary spatially and temporally. We project the changes by using CESM low‐warming experiments. In the experiments, the multiyear global mean surface temperatures will stabilize at 1.5°C and 2.0°C above the preindustrial level by the end of the 21st century. We find significant increases in seasonal cycle over both ocean and land. The increase is dominated by the enhancement of precipitation during wet season. The increased seasonal cycle is caused by the increase in water vapor over most regions except for part of the tropical ocean and some of the land regions, where the effects of circulation changes are remarkable. Key Points: The precipitation annual range, that is, the difference between wet and dry seasons, would increase by 3.90(5.27)% globally at 1.5(2)°C scenariosUnder the 2.0°C warming scenario, over 22% of the landmass will receive more precipitation in the wet season than that under the 1.5°C warmingThe increase in the precipitation annual range is due to the vertical moisture advection dominated by moisture increase with global warming [ABSTRACT FROM AUTHOR]

We analyze projected changes in climate extremes (extreme temperatures and heavy precipitation) in the multimodel ensembles of the fifth and sixth Coupled Model Intercomparison Projects (CMIP5 and CMIP6). The results reveal close similarity between both ensembles in the regional climate sensitivity of the projected multimodel mean changes in climate extremes, that is, their projected changes as a function of global warming. This stands in contrast to widely reported divergences in global (transient and equilibrium) climate sensitivity in the two multimodel ensembles. Some exceptions include higher warming in the South America monsoon region, lower warming in Southern Asia and Central Africa, and higher increases in heavy precipitation in Western Africa and the Sahel region in the CMIP6 ensemble. The multimodel spread in regional climate sensitivity is found to be large in both ensembles. In particular, it contributes more to intermodel spread in projected regional climate extremes compared with the intermodel spread in global climate sensitivity in CMIP6. Our results highlight the need to consider regional climate sensitivity as a distinct feature of Earth system models and a key determinant of projected regional impacts, which is largely independent of the models' response in global climate sensitivity. Plain Language Summary: Many articles analyze and compare global climate sensitivity in climate models, that is, how their global warming differs at a given level of CO2 concentrations. However, global warming is only one quantity affecting impacts. To assess human‐ and ecosystem‐relevant impacts, it is essential to evaluate the regional climate sensitivity of climate models, that is, how their regional climate features differ at a given level of global warming. We analyze here regional climate sensitivity in the new multimodel ensemble that will underlie the conclusions of the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). This ensemble of model projections is called the "Sixth Coupled Model Intercomparison Project" or CMIP6. We find that differences in regional climate sensitivity between models in CMIP6 often contribute more to the uncertainty of regional extremes projections than the uncertainty in global mean warming between models. Overall, the regional climate sensitivity features in the CMIP6 models' projections ensemble are very similar to those of the prior ensemble (CMIP5), although the model ensembles have been highlighted to differ in their global climate sensitivity over the 21st century. Key Points: Changes in climate extremes as a function of global warming are quasilinear and determine a "regional climate sensitivity" in CMIP5 and CMIP6The regional climate sensitivity of climate extremes is found to be very similar in CMIP5 and CMIP6, unlike global climate sensitivityModel spread in regional climate sensitivity in CMIP6 contributes more to uncertainty of projected extremes than global climate sensitivity [ABSTRACT FROM AUTHOR]

Drought has become a major threat to local sustainable development in dryland Asia, one of the largest grassland ecosystems in the world. However, empirical‐ and science‐based evidence regarding the extent of drought changes and the future trends of these changes in dryland Asia is variable and incomplete. Here, we first investigate the historical variations in drought conditions in dryland Asia, as measured by the drought intensity and arid area, using three widely used drought indices (the Palmer Drought Severity Index, the Standardized Precipitation Index, and the Standardized Precipitation Evapotranspiration Index). Then, we use Bayesian model averaging to reproduce the future drought conditions under two representative concentration pathways (RCP2.6 and RCP4.5) from the Coupled Model Intercomparison Project Phase 5 Earth system models. The Palmer Drought Severity Index, Standardized Precipitation Index, and Standardized Precipitation Evapotranspiration Index illustrate that dryland Asia has experienced an overall drying trend and an expansion of arid areas over the past 100 years (1901–2016). Both temperature and precipitation are projected to increase under both the 1.5 and 2.0 °C warming scenarios compared with the values from the reference period (1986–2005). The projected drought conditions in the 1.5 and 2.0 °C warming scenarios will worsen, especially across Kazakhstan and Northwest China. We found that the drought conditions under the 2.0 °C warming conditions will not be as severe as those under the 1.5 °C warming conditions due to the mitigating effect of the projected precipitation increase under RCP4.5. These results call for short‐term and long‐term mitigation and adaptation measurements for drought events in dryland Asia. Plain Language Summary: To avoid the negative impacts of climate warming, the Paris Agreement aims to pursue efforts to maintain the global warming increase at well below 1.5 and even 2.0 °C until the end of the century. Questions have been raised regarding the climate extremes in dryland Asia. Will drought issues become more severe under the context of global warming? Are the existing drought indices able to quantify and characterize the drought intensity and arid area in this region? Answers to these questions are crucial for the livelihood of millions of individuals, as these people rely on grassland biomass to feed both animals and farmers; however, the answers remain unclear. Here, we found that the projected drought severity and arid area will persistently increase under both the 1.5 and 2.0 °C global warming scenarios. We also found that the drought conditions under the 2.0 °C warming scenario will be mitigated relative to those under the 1.5 °C warming scenario due to the beneficial effect of adequate precipitation under representative concentration pathway 4.5. Kazakhstan and Northwest China might be severely affected by drought. Therefore, understanding future changes in drought conditions in dryland Asia is critical for developing adaptation measures to cope with the challenges of rapid climate change. Key Points: Future global climate change will impose severe drought issues in dryland Asia, including drying trends and expanded arid areasDrought conditions in dryland Asia under the 2.0 °C warming will not be as severe as those under the 1.5 °C warmingFuture drought conditions in Kazakhstan and Northwest China will likely be more severe in dryland Asian countries [ABSTRACT FROM AUTHOR]

In recent decades, grain self‐sufficiency has been a key security issue for certain countries, such as Russia, China, India, and France. Climate change may affect agricultural production and possibly influence the grain self‐sufficiency of some countries, threatening their food security. This article provides an updated integrated assessment of the impact of climate change on grain self‐sufficiency at the country level. The study links climatic variables projected by global climate models to economic variables simulated by a global multiregion multisector economic model. Although climate change may considerably reduce land productivity, our simulation results show that climate change in the long term modestly impacts regional grain self‐sufficiency, as the direct effects on yield are largely canceled out by changes in grain production via adaptation measures taken by producers in response to market signals. Behavioral changes of consumers also contribute modestly to cancel out the adverse impact on land productivity. In the RCP8.5 climate change scenario, the adverse impact of climate change on land productivity in 2100 may reach to 25% of the current level, but declines to 5% when changes in production and consumption are considered, thus indicating the role of long‐term adaptation by economic agents. Key Points: The country‐level impact of climate change on grain self‐sufficiency is studiedClimate change modestly impacts regional grain self‐sufficiency over the long termAdaption by producers and consumers markedly mitigates the impact of climate [ABSTRACT FROM AUTHOR]

Projecting climate impacts of a half‐degree warming increment is of high priority on post Paris Agreement science agendas. As the real world has already witnessed a 0.5°C global mean surface temperature warming increment, the observed climate changes associated with the half‐degree warming may be analogues for future projections. This hypothesis is examined by comparing the heat extreme changes in China derived from the observational records to projections of the Community Earth System Model (CESM) low‐warming experiment, which is the first short‐term stabilized simulation dedicated for the 1.5 and 2°C warming targets. The results of the CESM historical simulations are also evaluated. From the perspective of spatially aggregated, the heat extreme changes in China under the historical 0.5°C warming are detectable in observations. The nighttime extremes manifest more significant increase than daytime extremes. Heat extreme changes under the past half‐degree warming increment are reasonably captured in the historical simulations with slightly weaker magnitudes. The changes in the intensity indices in observations are better reproduced by the historical simulations than the frequency and duration indices. For the heat extreme changes in the future 0.5°C warming, the observational records can serve as conservative analogues in daytime extremes, while the nighttime extreme indices show comparable or weaker changes. The future reduction of anthropogenic aerosol emissions will amplify the increase of heat extremes in comparison to present day especially during daytime in China. Given the possibly intensified extremes associated with future aerosol reductions, more attention should be paid to the currently heavy polluted regions. Plain Language Summary: Since the Paris Agreement called for limiting the future global warming under 2°C and pursuing efforts to limit under 1.5°C, great efforts have been devoted to exploring the benefits of the 0.5°C less warming on natural and social systems. Since the world has already witnessed a 0.5°C warming increment, whether the associated observed climate changes can be analogues for future projections is an interesting and important question. Focusing on the heat extreme changes over continental China, we revisit the observational data sets to evaluate the performance of the Community Earth System Model (CESM) historical simulations and then compare the observed changes with the CESM 1.5°C/2°C future projections. We find that the heat extreme changes under the past 0.5°C warming increment are detectable in observations and can be well reproduced by the historical simulations. The changes of intensity indices in the observations are better reproduced by the model than the frequency and duration indices. For the daytime heat extremes, the observations only give the lower boundary for the projected changes in future 0.5°C warming. China may experience severer increase in daytime heat extremes due to possible aerosol reductions in the future. Our results would provide useful information to climate change adaption and risk management. Key Points: The increases of the general heat extremes under the past 0.5°C warming increment in the observational records are detectable in ChinaThe CESM historical simulations can reproduce the changes of the heat extremes in China but with slightly weaker magnitudesThe daytime extreme changes in observations can serve as conservative analogues for the future projections [ABSTRACT FROM AUTHOR]

Amplified regional warming suggests that some regions suffer more from global warming. However, present knowledge is still not enough to understand this paramount aspect of global warming. By using climate model simulations, we first highlight that regional warming amplifications directly following anthropogenic emission would torment many undeveloped countries. Then, we find that cloud has the largest contribution to polar amplification, rather than the frequently blamed sea ice decline. The summertime sea ice decline plays the second role in generating strong wintertime polar amplification via lagged energy release. Our findings also propose that heat uptake by the deeper ocean greatly favors the terrestrial amplification. Additionally, the cloud also shows its importance in helping dryland amplification. Our findings suggest that these robust regional warming amplifications are very likely inevitable under anthropogenic emission, therefore strictest global mitigation is required to prevent unacceptable warming over the high risk regions. Plain Language Summary: Amplified regional warming points out that some regions are more suffering under global warming. Thus, we performed this study to figure out robust regional warming amplifications directly following the anthropogenic greenhouse gas emission. We addressed the influences of these regional warming amplifications to human society, such an amplified dryland warming (relative to humid regions) has greater influences on some undeveloped countries. Furthermore, we achieved some new scientific findings that are crucial to understanding causes of amplified regional warming, such as cloud's dominant role on amplified pole warming (relative to lower‐latitudes) rather than the frequently blamed sea ice decline. We also found the important role of deeper ocean heat uptake and cloud in helping amplified land warming (relative to ocean) and amplified dryland warming, respectively. Taken together, our study greatly helps to understand human influences on regional climate change. Key Points: Human‐induced global warming has greater influences on some undeveloped countriesCloud has the largest contribution to polar amplification, rather than the frequently blamed sea ice declineHeat uptake by the deeper ocean greatly favors the terrestrial amplification [ABSTRACT FROM AUTHOR]

Sulfate geoengineering could mitigate global warming via injecting SO2 into the stratosphere. However, its impacts on regional climate might lead to adverse consequences for local agriculture. In this study, we simulated the impacts of sulfate geoengineering on rice yield in China both with sufficient irrigation (irrigated) and without irrigation (rainfed). We used Geoengineering Model Intercomparison Project G4 climates from six climate models to force the ORYZA version 3 crop model to simulate rice yields under sulfate geoengineering scenario. G4 prescribes a sulfate injection to offset the radiative forcing in the Representative Concentration Pathway (RCP) 4.5 scenario. Results indicated that during the last 15 years of G4 sulfate geoengineering (i.e., 2055–2069), the implementation of sulfate geoengineering increases rice yields in most areas in China comparing with that without the implementation of sulfate geoengineering (i.e., RCP4.5), with a yield increase of 5.3 ± 5.7% for irrigated yield and 4.8 ± 7.3% for rainfed yield. After the termination of sulfate geoengineering, the irrigated rice yield in G4 is still significantly higher than that in RCP4.5, but such increase is not significant for rainfed yield. Temperature is always the dominant factor that drives the rice yield change no matter under irrigated or rainfed conditions, but the effect from solar radiation cannot be ignored in southern China. Key Points: G4 sulfate geoengineering is projected to increase irrigated rice yield in China by 5.3 ± 5.7%G4 sulfate geoengineering is projected to increase rainfed rice yield in China by 4.8 ± 7.3%Temperature is the dominant factor driving the rice yield changes [ABSTRACT FROM AUTHOR]

We estimate the effects of climate anomalies (heat stress and drought) on annual maize production, variability, and trend from the country level to the global scale using a statistical model. Moderate climate anomalies and extremes are diagnosed with two indicators of heat stress and drought computed over maize growing regions during the most relevant period of maize growth. The calibrated model linearly combines these two indicators into a single Combined Stress Index. The Combined Stress Index explains 50% of the observed global production variability in the period 1980–2010. We apply the model on an ensemble of high‐resolution global climate model simulations. Global maize losses, due to extreme climate events with 10‐year return times during the period 1980–2010, will become the new normal already at 1.5 °C global warming levels (approximately 2020s). At 2 °C warming (late 2030s), maize areas will be affected by heat stress and drought never experienced before, affecting many major and minor production regions. Plain Language Summary: Global warming is negatively affecting several aspects of ecosystems and societies. This study analyzes the impact of climate on global and regional maize production in the past and in the future. The effects of warmer temperatures and lack of rain on maize production is first analyzed from reported national maize production time series, and these relationships are then projected into the future, using state‐of‐the‐art global climate model simulations. The worse climate events causing the larger maize production losses observed in the past will become normal already at the global warming level of 1.5 °C compared to the preindustrial period. Our findings highlight the importance of Paris Agreement mitigation goals to hold the increase of global temperature well below 2 °C and pursuing efforts to limit increase to 1.5 °C, as well as the need of identifying and adopting efficient adaptation measures. Key Points: Since the 1980s, climate has become more favorable for maize production in the United States, balancing increased heat and drought impacts elsewhereHeat and drought impacts will become common in several regions that rely on maize production, already at the 1.5 degrees Celsius global warming levelUnprecedented losses are projected to become common in most maize producing regions (including the United States) at 2 degrees Celsius global warming [ABSTRACT FROM AUTHOR]

Abstract: Even if global warming is kept below +2°C, European agriculture will be significantly impacted. Soil degradation may amplify these impacts substantially and thus hamper crop production further. We quantify biophysical consequences and bracket uncertainty of +2°C warming on calories supply from 10 major crops and vulnerability to soil degradation in Europe using crop modeling. The Environmental Policy Integrated Climate (EPIC) model together with regional climate projections from the European branch of the Coordinated Regional Downscaling Experiment (EURO‐CORDEX) was used for this purpose. A robustly positive calorie yield change was estimated for the EU Member States except for some regions in Southern and South‐Eastern Europe. The mean impacts range from +30 Gcal ha−1 in the north, through +25 and +20 Gcal ha−1 in Western and Eastern Europe, respectively, to +10 Gcal ha−1 in the south if soil degradation and heat impacts are not accounted for. Elevated CO2 and increased temperature are the dominant drivers of the simulated yield changes in high‐input agricultural systems. The growth stimulus due to elevated CO2 may offset potentially negative yield impacts of temperature increase by +2°C in most of Europe. Soil degradation causes a calorie vulnerability ranging from 0 to 50 Gcal ha−1 due to insufficient compensation for nutrient depletion and this might undermine climate benefits in many regions, if not prevented by adaptation measures, especially in Eastern and North‐Eastern Europe. Uncertainties due to future potentials for crop intensification are about 2–50 times higher than climate change impacts. [ABSTRACT FROM AUTHOR]

Particulate matter with the diameter smaller than 2.5 μm (PM2.5) poses health threats to human population. Regardless of efforts to regulate the pollution sources, it is unclear how climate change caused by greenhouse gases (GHGs) would affect PM2.5 levels. Using century‐long ensemble simulations with Community Earth System Model 1 (CESM1), we show that, if the anthropogenic emissions would remain at the level in the year 2005, the global surface concentration and atmospheric column burden of sulfate, black carbon, and primary organic carbon would still increase by 5%–10% at the end of 21st century (2090–2100) due to global warming alone. The decrease in the wet removal flux of PM2.5, despite an increase in global precipitation, is the primary cause of the increase in the PM2.5 column burden. Regionally over North America and East Asia, a shift of future precipitation toward more frequent heavy events contributes to weakened wet removal fluxes. Our results suggest climate change impact needs to be accounted for to define the future emission standards necessary to meet air quality standard. [ABSTRACT FROM AUTHOR]

Abstract: The 2015 Paris Agreement aims to limit global warming to well below 2 K above preindustrial levels, and to pursue efforts to limit global warming to 1.5 K, in order to avert dangerous climate change. However, current greenhouse gas emissions targets are more compatible with scenarios exhibiting end‐of‐century global warming of 2.6–3.1 K, in clear contradiction to the 1.5 K target. In this study, we use a global climate model to investigate the climatic impacts of using solar geoengineering by stratospheric aerosol injection to stabilize global‐mean temperature at 1.5 K for the duration of the 21st century against three scenarios spanning the range of plausible greenhouse gas mitigation pathways (RCP2.6, RCP4.5, and RCP8.5). In addition to stabilizing global mean temperature and offsetting both Arctic sea‐ice loss and thermosteric sea‐level rise, we find that solar geoengineering could effectively counteract enhancements to the frequency of extreme storms in the North Atlantic and heatwaves in Europe, but would be less effective at counteracting hydrological changes in the Amazon basin and North Atlantic storm track displacement. In summary, solar geoengineering may reduce global mean impacts but is an imperfect solution at the regional level, where the effects of climate change are experienced. Our results should galvanize research into the regionality of climate responses to solar geoengineering. [ABSTRACT FROM AUTHOR]

Global mean surface temperatures ( GMST) exhibited a smaller rate of warming during 1998-2013, compared to the warming in the latter half of the 20th Century. Although, not a 'true' hiatus in the strict definition of the word, this has been termed the 'global warming hiatus' by IPCC (2013). There have been other periods that have also been defined as the 'hiatus' depending on the analysis. There are a number of uncertainties and knowledge gaps regarding the 'hiatus.' This report reviews these issues and also posits insights from a collective set of diverse information that helps us understand what we do and do not know. One salient insight is that the GMST phenomenon is a surface characteristic that does not represent a slowdown in warming of the climate system but rather is an energy redistribution within the oceans. Improved understanding of the ocean distribution and redistribution of heat will help better monitor Earth's energy budget and its consequences. A review of recent scientific publications on the 'hiatus' shows the difficulty and complexities in pinpointing the oceanic sink of the 'missing heat' from the atmosphere and the upper layer of the oceans, which defines the 'hiatus.' Advances in 'hiatus' research and outlooks (recommendations) are given in this report. [ABSTRACT FROM AUTHOR]

Recent trends and climate models suggest that the Arctic summer sea ice cover is likely to be lost before climate interventions can stabilize it. There are environmental, socioeconomic, and sociocultural arguments for, but also against, restoring and sustaining current conditions. Even if global warming can be reversed, some people will experience ice-free summers before perennial sea ice begins to return. We ask: How will future generations feel about bringing sea ice back where they have not experienced it before? How will conflicted interests in ice-covered vs. ice-free conditions be resolved? What role will science play in these debates? [ABSTRACT FROM AUTHOR]