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ABSTRACT Aim Location Time Period Major Taxa Studied Methods Results Main Conclusions Climate extremes are becoming more frequent under global warming, with substantial repercussions for vegetation growth. The degree to which climate extremes increase the risk of high‐impact events on vegetation growth is of high concern.Northern Hemisphere (north of 30°N).From 2001 to 2022.Plants.We utilised solar‐induced chlorophyll fluorescence (SIF) and the normalised difference vegetation index (NDVI) as proxies for vegetation growth. We performed event coincidence and sensitivity analyses to attribute satellite‐derived vegetation growth extremes to diverse climate extremes (extreme heat, cold, wet and drought) in the Northern Hemisphere.Our results showed that extreme heat and cold were the main climatic extremes that induced positive and negative vegetation growth extremes north of 30°N, respectively, mainly in cold and humid ecosystems (boreal and temperate forests). Water‐related extreme events accounted for less than one‐third of vegetation extremes. The contribution of drought to positive vegetation growth extreme events (approximately 17%), mainly in cold and humid ecosystems, was even slightly higher than that of extreme wet (approximately 12%), which predominantly impacted relatively warm and arid ecosystems (croplands and temperate grasslands). We further identified potential climatic thresholds that could reverse vegetation growth responses to climate extremes (temperature is 12.5°C and climatic water deficit is ‐60 mm, approximately). We also showed that the past two decades of warming and precipitation changes did not induce a shift in the main climatic drivers of vegetation extremes across northern ecosystems.Our results emphasise the crucial role of background hydrothermal conditions in the attribution of vegetation growth extremes to diverse climate extremes across northern ecosystems and have substantial implications for predicting how Northern Hemisphere vegetation will respond to increasing climate extremes in the future. [ABSTRACT FROM AUTHOR]

The analysis of the ASTC1 sediment core from the south Aegean Sea region offers critical insights into the complex interplay of geological and climatic factors over the Holocene period. The data reveals fluctuating climatic conditions during the last 8.7 ka as seen through the elemental concentrations obtained by XRF core scanning combined with a qualitative mineral analysis within a robust chronological framework. Short-term fluctuations in both Ti/Al and Zr/Si ratios suggest brief oscillations of increased aridity which partially coincide with the Holocene "Rapid Climate Change" events (RCCs). Among them, the most pronounced in our record are those centered between 8.5–8 ka, 3–2.5 ka (Greek Dark Ages), and 0.6–0.3 ka (Little Ice Age). The arid and humid events identified in the sediment record align with major archaeological periods in Greece, suggesting a potential influence of climatic conditions on the development and decline of civilizations in the region. Moreover, a general arid trend as of 6 ka toward the present was evidenced in our record and aligns with other high-resolution climatic data from the Northern Hemisphere, suggesting climatic teleconnections. Spectral analysis of the ASTC1 record reveals cyclical climate patterns with periodicities of approximately 2500, 1200, and 550 years, which coincide with the Bond and Hallstatt cycles. The phase relation of these cycles in our record, the Greenland ice record, and the North Atlantic Drift ice indices show that colder conditions in the higher latitudes are expressed as events of enhanced aridity in our record and generally in the lower latitudinal regions. [ABSTRACT FROM AUTHOR]

The skill of subseasonal (multiweek) forecasts of tropical‐cyclone (TC) occurrence over the Northern Hemisphere is examined in the Australian Bureau of Meteorology's (BoM) multiweek to seasonal prediction system, ACCESS‐S2. ACCESS‐S2 shows a good representation of the spatial distribution of TCs in the Northern Hemisphere; however, TC track frequency is generally underpredicted in the western North Pacific to the east of the Philippines and in the eastern North Pacific. The reduced activity relative to observations could be due to a significant positive bias in 850–200‐hPa wind shear in both of these regions, as well as a significant negative sea‐surface temperature (SST) bias in the eastern North Pacific. Despite biases in climatological TC frequency, the observed change in TC track frequency across the Northern Hemisphere with the phase of the Madden–Julian Oscillation (MJO) is well captured by ACCESS‐S2. Changes in the large‐scale environment (e.g., precipitation, 600‐hPa relative humidity, 850‐hPa absolute vorticity and 850–200‐hPa wind shear) are also well represented, with the location and size of the anomalies comparable to ERA‐Interim, apart from SST which shows a different response during some phases. ACCESS‐S2 shows skill relative to climatology for multiweek predictions of TC occurrence out to week 5 in the western North Pacific, eastern North Pacific and North Atlantic; and out to week 2 for the North Indian Ocean. Assessment of real‐time forecasts for Typhoon Rai (December 2021) showed that ACCESS‐S2 provided good guidance of the development and potential landfall of a TC in the Philippines at four weeks lead time. [ABSTRACT FROM AUTHOR]

In this paper, we used data from 42 soil temperature observation sites in permafrost regions throughout the Northern Hemisphere to analyze the characteristics and variability in soil temperature. The observation data were used to evaluate soil temperature simulations at different depths from 10 CMIP6 models in the permafrost region of the Northern Hemisphere. The results showed that the annual average soil temperature in the permafrost regions in the Northern Hemisphere gradually decreased with increasing latitude, and the soil temperature gradually decreased with depth. The average soil temperatures at different depths were mainly concentrated around 0 °C. The 10 CMIP6 models performed well in simulating soil temperature, but most models tended to underestimate temperatures compared to the measured values. Overall, the CESM2 model yielded the best simulation results, whereas the CNRM-CM6-1 model performed the worst. The change trends in annual average soil temperature across the 42 sites ranged from −0.17 °C/10a to 0.41 °C/10a from 1900 to 2014, the closer to the Arctic, the faster the soil warming rate. The rate of soil temperature change also varied at different depths between 1900–2014 and 1980–2014. The rate of soil temperature change from 1980 to 2014 was approximately three times greater than that from 1900 to 2014. [ABSTRACT FROM AUTHOR]

Strangely, the palimpsest of human occupation is often far less visible in the city than it is in wilder spaces. Artist, architect, researcher and educator Kirsty Badenoch describes an exploratory expedition to draw out these ghosts within the rugged landscapes of the Scottish Highlands, and a subsequent exhibition of the work through diary entries and photographic forms. The work itself is made through transcriptive collaborations with the volatile climate and flora and fauna of the site, creating a tale of palimpsestuous relationships that dislocate the artistic self as nature leads the dance, or at the very least calls the tune. [ABSTRACT FROM AUTHOR]

Retrogressive thaw slumps (RTSs) caused by the thawing of ground ice on permafrost slopes have dramatically increased and become a common permafrost hazard across the Northern Hemisphere during previous decades. However, a gap remains in our comprehensive understanding of the spatial controlling factors, including the climate and terrain, that are conducive to these RTSs at a global scale. Using machine learning methodologies, we mapped the current and future RTSs susceptibility distributions by incorporating a range of environmental factors and RTSs inventories. We identified freezing-degree days and maximum summer rainfall as the primary environmental factors affecting RTSs susceptibility. The final ensemble susceptibility map suggests that regions with high to very high susceptibility could constitute (11.6 ± 0.78)% of the Northern Hemisphere's permafrost region. When juxtaposed with the current (2000–2020) RTSs susceptibility map, the total area with high to very high susceptibility could witness an increase ranging from (31.7 ± 0.65)% (SSP585) to (51.9 ± 0.73)% (SSP126) by the 2041–2060. The insights gleaned from this study not only offer valuable implications for engineering applications across the Northern Hemisphere, but also provide a long-term insight into the potential change of RTSs in permafrost regions in response to climate change.

A high-quality snow depth product is very import for cryospheric science and its related disciplines. Current long time-series snow depth products covering the Northern Hemisphere can be divided into two categories: remote sensing snow depth products and reanalysis snow depth products. However, existing gridded snow depth products have some shortcomings. Remote sensing-derived snow depth products are temporally and spatially discontinuous and tend to underestimate snow depth, while reanalysis snow depth products have coarse spatial resolutions and great uncertainties. To overcome these problems, in our previous work we proposed a novel data fusion framework based on Random Forest Regression of snow products from Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), Advanced Microwave Scanning Radiometer-2 (AMSR2), Global Snow Monitoring for Climate Research (GlobSnow), the Northern Hemisphere Snow Depth (NHSD), ERA-Interim, and Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), incorporating geolocation (latitude and longitude), and topographic data (elevation), which were used as input independent variables. More than 30,000 ground observation sites were used as the dependent variable to train and validate the model in different time periods. This fusion framework resulted in a long time series of continuous daily snow depth product over the Northern Hemisphere with a spatial resolution of 0.25°. Here, we compared the fused snow depth and the original gridded snow depth products with 13,272 observation sites, showing an improved precision of our product. The evaluation indices of the fused (best original) dataset yielded a coefficient of determination R2 of 0.81 (0.23), Root Mean Squared Error (RMSE) of 7.69 (15.86) cm, and Mean Absolute Error (MAE) of 2.74 (6.14) cm. Most of the bias (88.31%) between the fused snow depth and in situ observations was in the range of −5 cm to 5 cm. The accuracy assessment of independent snow observation sites – Sodankylä (SOD), Old Aspen (OAS), Old Black Spruce (OBS), and Old Jack Pine (OJP) – showed that the fused snow depth dataset had high precision for snow depths of less than 100 cm with a relatively homogeneous surrounding environment. The results of random point selection and independent in situ site validation show that the accuracy of the fused snow depth product is not significantly improved in deep snow areas and areas with complex terrain. In the altitude range of 100 m to 2000 m, the fused snow depth had a higher precision, with R2 varying from 0.73 to 0.86. The fused snow depth had a decreasing trend based on the spatiotemporal analysis and Mann-Kendall trend test method. This fused snow depth product provides the basis for understanding the temporal and spatial characteristics of snow cover and their relation to climate change, hydrological and water cycle, water resource management, ecological environment, snow disaster and hazard prevention.

The investigation of the height variations of the westerly in the mid-latitudes of the Northern Hemisphere is crucial for monitoring changes in the intricate atmospheric system. This study examined the hypothesis of changes in the thickness of the westerly domain by analyzing the height of the 500 hPa pressure level. To this end, monthly data from the European Centre for Medium-Range Weather Forecasts (ECMWF) spanning from 1959 to 2021 was utilized to investigate three components: geopotential height (GH), zonal, and meridional wind components. The dataset underwent statistical tests, including trend analysis using Least Squares Error linear regression (LSE-LR) and shift (jump) analysis using the Standard Normal Homogeneity Test (SNHT). The results revealed a significant increasing trend in the height of the troposphere and the westerlies in the mid-latitudes of the Northern Hemisphere, accompanied by significant fluctuations, indicating an increase in the height of the 500 hPa pressure level and a decrease in the thickness of the westerly domain. The extent of these trends was observed to be greater in cold months, particularly in January and February, while the changes were minimal in November. Notably, the spatial distribution of upward jumps, indicative of change, was highest in January, July, and August in the eastern and southeastern regions of Asia. Furthermore, the convergence section of the westerlies trough exhibited a substantial number of jumps, particularly in March, spanning Central America and southern parts of North America. Regarding decadal coincidence onset, the highest number of jumps occurred in February, encompassing the western Pacific Ocean, western Atlantic Ocean, Eastern Europe, and western Asia. The end of these jumps coincided in February, and the spatial proximity of the end times was closer compared to the onset times in February, March, April, July, and August. [ABSTRACT FROM AUTHOR]

The vegetation patterns in high-latitude and high-altitude regions (HLAR) of the Northern Hemisphere are undergoing significant changes due to the combined effects of global warming and human activities, leading to increased uncertainties in vegetation phenological assessment. However, previous studies on vegetation phenological changes often relied on long-term time series of remote sensing products for evaluation and lacked comprehensive analysis of driving factors. In this study, we utilized high temporal resolution seamless MODIS products (MODIS-NDVISDC and MODIS-EVI2SDC) to assess the vegetation phenological changes in High-Latitude-Altitude Regions (HLAR) of the Northern Hemisphere. We quantified the differences in vegetation phenology among different land-use types and determined the main driving factors behind vegetation phenological changes. The results showed that the length of the growing season (LOS) derived from MODIS-NDVISDC was 8.9 days longer than that derived from MODIS-EVI2SDC, with an earlier start of the growing season (SOS) by 1.5 days and a later end of the growing season (EOS) by 7.4 days. Among different vegetation types, deciduous needleleaf forests exhibited the fastest LOS extension (p < 0.01), while croplands showed the fastest LOS reduction (p < 0.05). Regarding land-use transitions, the conversion of built-up land to forest and grassland had the longest LOS. In expanding agricultural areas, the LOS of land converted from built-up land to cropland was significantly higher than that of other land conversions. We analyzed human activities and found that as the human footprint gradient increased, the LOS showed a decreasing trend. Among the climate-related factors, the dominant response of phenology to temperature was the strongest in the vegetation greening period. During the vegetation browning period, the temperature control was weakened, and the control of radiation and precipitation was enhanced, accounting for 20–30% of the area, respectively. Finally, we supplement and prove that the highest contributions to vegetation greening in the Northern Hemisphere occurred during the SOS period (May–June) and the EOS period (October). Our study provides a theoretical basis for vegetation phenological assessment under global change. It also offers new insights for land resource management and planning in high-latitude and high-altitude regions. [ABSTRACT FROM AUTHOR]

Biological soil crusts (biocrusts) have crucial ecological functions in dryland ecosystems, yet understanding the variations in soil microbial biomass within biocrusts across diverse ecosystems, climates and soil conditions remains limited. This knowledge gap constrains our understanding of how microbial communities within biocrusts regulate terrestrial carbon and nitrogen cycling. Hence, we conducted a meta‐analysis using 255 paired observations from 42 study sites across the northern temperate ecosystem. The analysis revealed that biocrusts harbour significantly higher soil microbial biomass carbon and nitrogen (SMBC and SMBN, respectively) levels than bare (non‐biocrust) soil across all habitat types. Notably, deeper soil layers (5–10 and >10 cm) accumulated less SMBC and SMBN than biocrust and biocrust–5‐cm soil, revealing that biocrusts influence shallow soil environments. Ecosystem type, soil texture, depth and season emerged as key factors influencing the distribution of SMBC within biocrusts. Of particular interest, lichen biocrusts accumulated the most SMBC compared with other biocrust types. Furthermore, the difference in SMBC between biocrust and non‐biocrust soils was more pronounced in oligotrophic habitats (e.g., desert, grassland, sand and sandy loam soils) than in eutrophic habitats (e.g., forest and loam soils). Random forest analysis confirmed that soil variables affected SMBC accumulation in biocrusts more than climatic factors. Soil organic carbon (SOC), as the primary source of SMBC, could be the most important determinant. Moreover, the disparity between non‐biocrust SMBC and biocrust SMBC increased with increasing mean annual temperature (MAT) or decreasing altitude. These insights underscore the substantial contribution of lichen biocrusts to SMBC and emphasize the need to incorporate this knowledge into regional models for predicting the effects of climate change on soil carbon budgets within biocrust microbiomes in temperate ecosystems of the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

The tropopause serves a critical role in shaping global and regional weather and climate dynamics. Changes in tropopause characteristics can significantly impact other atmospheric components, thereby influencing Earth's climate systems. In the long run, variations in tropopause features can lead to shifts in the thermal, dynamic, and chemical properties of the tropospheric layer. This study aims to investigate the descriptive attributes of tropopause pressure levels (TPLs) during different months, as well as the temporal and spatial trends in TPL across the Northern Hemisphere spanning from 1979 to 2022. Utilizing ERA5 temperature data for the 700 to 50 hPa range, the tropopause was identified using the lapse rate of tropopause (LRT), and its changes were analyzed employing the linear regression model with the least squares error approach. The results indicated that the spatial pattern of TPLs changed across various latitudes varies seasonally. Generally, the changes in TPLs did not exhibit a linear relationship with latitude, and in most observed months, the highest and lowest TPLs did not correspond to the lowest and highest latitudes, respectively. Examination of the trend in TPLs revealed that in numerous significant areas across different seasons, the trends were statistically insignificant. Where significant, the trends predominantly indicated negative changes (decreases), suggesting a reduction in pressure and potentially an increase in tropopause altitude in these regions, possibly reflecting the influence of global warming. [ABSTRACT FROM AUTHOR]

Evapotranspiration (ET) is a crucial link in water circulation. It plays an important role in the global water cycle and surface energy balance, and has significant impacts on climate, ecosystems, and water resources management. Therefore, the quality of evapotranspiration data is crucial for the precise management of global water resources. This study conducted accuracy validation and spatiotemporal comparison of three ET products in the Northern Hemisphere, selecting the ET products that is more suitable for the Northern Hemisphere, providing suggestions for strengthening the combination of remote sensing and ground observation research. Using the monthly average measured data from FluxNet2015 flux sites to verify three ET products, it was found that PML&lowbar; V2 product has the highest accuracy in the Northern Hemisphere, followed by GLDAS, and finally MOD16A2, with correlation coefficients R of 0.66, 0.57, and 0.56, respectively; The root mean square error (RMSE) is 2.46, 5.68, and 12.42 mm/month, respectively; The average biases are 14.36%, 16.86%, and 35.02%, respectively. The GLDAS ET product has the ability to monitor daily scale ET, and the consistency between the daily average estimated value and the measured value at the flux tower site is high. The correlation coefficient R is 0.74, and the RMSE and Bias are 1.62mm/day and 27.90%, respectively. Overall, on the time scale, all three ET products can simulate the seasonal changes in the Northern Hemisphere, with higher summer evapotranspiration and lower winter evapotranspiration. The three ET products in summer all have overestimation phenomena on different land cover types, and the simulation results in other seasons are better than the ground observation values. Among them, MOD16A2 performs the worst, and the overestimation phenomenon is the most obvious. In addition, during the period from 2001 to 2020, except for arid areas, the spatial distribution of the three ET products was relatively consistent in most regions, with a correlation coefficient R greater than 0.6. This study provides scientific recommendations for selecting suitable ET data sources for conducting evapotranspiration studies in the Northern Hemisphere by evaluating the uncertainty and product quality of different ET products. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are some of the most biodiverse habitats, but they are among the most endangered due to human activities. In this context, beavers represent a nature‐based solutions to preserve and repair freshwater ecosystem, given their important role as ecosystem engineers. However, in an environment modified by humans, beaver activities frequently create conflicts masking the positive effects of this rodent. Therefore, the management of beaver populations and human–beaver conflicts is needed.This article investigates the literature about beaver management through a bibliometric analysis to understand past, current, and future response. Moreover, it quantifies the number of studies that consider beavers as a resource, and it identifies the emerging themes in the field.The bibliometric analysis was performed considering a total of 415 documents with the software VOSviewer and the R web interface for bibliometrix Biblioshiny.The analysis presented here provides a complete view of past, present, and future management approaches and responses at the base of beaver management strategies. Three main results emerged. Firstly, a rising tendency in the number of publications about beavers that are directly linked to the populations development and spread has detected. Secondly, only 4.3% of scientific literature has referred to beaver‐related restoration. Thirdly, the 'human perceptions' has resulted in the emerging field investigated.Findings suggest that there is a lot of research interest about beaver management. The beaver is still poorly managed as a tool for freshwater ecosystem restoration. The management is shifting from studies focused more so on beaver ecology to others mainly focused on the beaver effects and the human dimension.This review provides a starting point for future research on beavers and suggests the development of socio‐ecological management models that consider benefits and impacts of beavers. This will help the decision‐making process of conservation and restoration initiatives. [ABSTRACT FROM AUTHOR]

Based on the ERA5 reanalysis data for the period 1979–2021, the authors have quantified the seasonal and regional connections between significant wave heights and changes in cyclone activity in the atmosphere of the Northern Hemisphere. The contribution of extratropical cyclones to the formation of the corresponding features and variations of sea waves is evaluated. The maxima of the extreme sea wave occurrence frequency in winter and summer corresponds to sea areas with an increased frequency of cyclones, in particular, over the Pacific and Atlantic oceans. It has been found that the contribution of extratropical cyclones to the generation of significant wave heights reaches 70% in winter and 50% in summer. The largest contribution is associated with intense cyclones: 90% in winter and 40% in summer. [ABSTRACT FROM AUTHOR]

Concurrent heat extremes (CHEs) are becoming increasingly common in the mid‐high latitudes across the Northern Hemisphere (NH), underscoring the need to comprehend their spatiotemporal characteristics and underlying causes. Here we reveal a phase‐locking behavior in Wave‐4 pattern, particularly after mid‐1990s, giving rise to a prominent CHE mode akin to heat extreme pattern observed in 2022, which swept most NH regions. Wave‐4 pattern significantly amplifies the likelihood of CHEs in Eastern Europe (∼30%), Northeast Asia (∼25%), and northwestern coast of North America (∼15%), while reducing the likelihood in central North America and northern Central Asia. During 1979–2022, the identified pattern accounted for over 69.7% of the trends in heat extremes over the mid‐high latitudes of the NH, directly exposing approximately 333.5 million people to heat extremes. Observations and simulations indicate that radiation anomalies over Eastern European Plain and West Siberian Plain play pivotal roles as primary forcing sources for Wave‐4 pattern. Plain Language Summary: Researchers have found that concurrent heat extremes are becoming more common in the Northern Hemisphere. This study discovered that a specific weather pattern, called as Wave‐4, became more prominent after the mid‐1990s and is linked to these heat extremes. This pattern increases the probability of heatwave occurrences in Eastern Europe, Northeast Asia, and northwestern coast of North America while decreasing them in central North America and northern Central Asia. Between 1979 and 2022, the identified Wave‐4 pattern contributed to more than two‐thirds of the increase in heat extremes in the northern hemisphere, affecting around 333.5 million people. It is also determined that unusual radiation levels over the Eastern European Plain and West Siberian Plain are significant factors contributing to the Wave‐4 pattern. This information helps us better understand the causes and characteristics of heat extremes in different parts of the world. Key Points: The Phase‐locked Rossby wave‐4 pattern dominates the concurrent heat extremes across the Northern HemisphereThe identified pattern exposed approximately 333.5 million people to heat extremesRadiation anomalies over the Eastern European Plain and West Siberian Plain play pivotal roles as forcing sources of the pattern [ABSTRACT FROM AUTHOR]

We have obtained quantitative estimates of the spatial and seasonal features of the characteristics of anticyclones in the atmosphere of the Northern Hemisphere and their changes in recent decades using ERA5 reanalysis data (1979–2021). A high correlation between the interannual variations of the mean seasonal occurence of anticyclones and near-surface temperature over extensive regions in the extratropical latitudes of the Northern Hemisphere is noted. According to the estimates, up to 60% of the interannual variance of near-surface temperature in winter and summer is associated with variations in the mean seasonal occurence of anticyclones and up to 50% with variations of intense winter and summer anticyclones. [ABSTRACT FROM AUTHOR]

Extratropical cyclones influence midlatitude surface weather directly via precipitation and wind and indirectly via upscale feedbacks on the large‐scale flow. Biases in cyclone frequency and characteristics in medium‐range to subseasonal numerical weather prediction might therefore hinder exploitation of potential predictability on these timescales. We thus, for the first time, identify and track extratropical cyclones in 20 years (2000–2020) of subseasonal ensemble reforecasts from the European Centre for Medium‐Range Weather Forecasts (ECMWF) in the Northern Hemisphere in all seasons. The reforecasts reproduce the climatology of cyclone frequency and life‐cycle characteristics qualitatively well up to six weeks ahead. However, there are significant regional biases in cyclone frequency, which can result from a complex combination of biases in cyclone genesis, size, location, lifetime, and propagation speed. Their magnitude is largest in summer, with the strongest regional deficit of cyclones of more than 30% in the North Atlantic, relatively large in spring, and smallest in winter and autumn. Moreover, the reforecast cyclones reach too‐high intensities during most seasons, although intensification rates are captured well. An overestimation of cyclone lifetime might partly but not exclusively explain this intensity bias. While the cyclone bias patterns often appear in lead‐time weeks 1 and 2, their magnitudes typically grow further at subseasonal lead times, in some cases up to weeks 5 and 6. Most of the dynamical sources of these biases thus likely appear in the early medium range, but sources on longer timescales probably contribute to the further increase of biases with lead time. Our study provides a useful basis to identify, better understand, and ultimately reduce biases in the large‐scale flow and in surface weather in subseasonal weather forecasts. Given the considerable biases during summer, when subseasonal predictions of precipitation and surface temperature will become increasingly important, this season deserves particular attention for future research. [ABSTRACT FROM AUTHOR]

The northern bat (Eptesicus nilssonii) is the most northern bat species in the world. Its distribution covers whole Eurasia, and the species is thus well adapted to different habitat types. However, recent population declines have been reported and rapid conservation efforts are needed. Here we present a high-quality de novo genome assembly of a female northern bat from Finland (BLF_Eptnil_asm_v1.0). The assembly was generated using a combination of Pacbio and Omni-C technologies. The primary assembly comprises 726 scaffolds spanning 2.0 Gb, represented by a scaffold N50 of 102 Mb, a contig N50 of 66.2 Mb, and a BUSCO completeness score of 93.73%. Annotation of the assembly identified 20,250 genes. This genome will be an important resource for the conservation and evolutionary genomic studies especially in understanding how rapid environmental changes affect northern species. [ABSTRACT FROM AUTHOR]

The analysis of spatial and temporal variability in the number of non-Gaussian extreme anomalies of climatic parameters was carried out for both the initial time series and synoptic variability in the troposphere of the Northern Hemisphere over the period 1979–2018, based on ERA-Interim reanalysis data. There are predominantly three types of empirical distribution densities at 850 hPa, each characterizing the processes of advective and convective heat transfer. At the beginning of the 21st century, compared to the end of the 20th century, there was an increase in the number of anomalies in vertical wind speed and specific humidity for the Northern Hemisphere. Additionally, there is an increase in the number of zonal wind speed anomalies in the low and middle latitudes. Regions with the maximum number of anomalies are primarily located over the continents, while for vertical wind speed anomalies, they are predominantly over the oceans. The application of R/S analysis and multifractal analysis has established that the identified tendencies (which are persistent processes) will continue in the identified regions. The time series of non-Gaussian anomalies (both initial and synoptic scales) exhibit a long-term memory of approximately four years, and synoptic extreme anomalies were found to be more predictable. [ABSTRACT FROM AUTHOR]

In this paper, we used data from 42 soil temperature observation sites in permafrost regions throughout the Northern Hemisphere to analyze the characteristics and variability in soil temperature. The observation data were used to evaluate soil temperature simulations at different depths from 10 CMIP6 models in the permafrost region of the Northern Hemisphere. The results showed that the annual average soil temperature in the permafrost regions in the Northern Hemisphere gradually decreased with increasing latitude, and the soil temperature gradually decreased with depth. The average soil temperatures at different depths were mainly concentrated around 0 °C. The 10 CMIP6 models performed well in simulating soil temperature, but most models tended to underestimate temperatures compared to the measured values. Overall, the CESM2 model yielded the best simulation results, whereas the CNRM-CM6-1 model performed the worst. The change trends in annual average soil temperature across the 42 sites ranged from −0.17 °C/10a to 0.41 °C/10a from 1900 to 2014, the closer to the Arctic, the faster the soil warming rate. The rate of soil temperature change also varied at different depths between 1900–2014 and 1980–2014. The rate of soil temperature change from 1980 to 2014 was approximately three times greater than that from 1900 to 2014.

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Changes in vegetation phenology are important contributors to seasonal climate change over the northern land surface. However, the biogeophysical effects of phenological shifts on land surface temperature (LST) remain uncertain. Here, we demonstrated the sensitivity of LST to advanced start of growing season (SOS) and delayed end of growing season (EOS) during corresponding green‐up and senescence periods over northern deciduous forests. Moreover, the mechanism responsible for LST sensitivity was assessed by quantifying the contributions of biogeophysical properties to LST sensitivity by applying a two resistance mechanism method to an experimental set using Community Land Model version 5. LST sensitivities to advanced SOS and delayed EOS were −2.1 × 10−2 K day−1 and −2.8 × 10−2 K day−1, respectively, indicating cooling effects by phenological shifts. The different responses of the aerodynamic resistance to SOS and EOS could explain the higher LST sensitivity to EOS than that to SOS. The decrease in the aerodynamic resistance in response to delayed EOS was three times larger than that to advanced SOS, thereby inducing a larger surface cooling effect during senescence period through enhanced turbulent heat transfer. Thus, the reduced aerodynamic resistance could explain the cooling effect of the phenological shift, which is an important consideration for projecting seasonal climate change. Plain Language Summary: The impact of phenological shifts in northern forests on land surface temperature (LST) is important for their potential to mitigate anthropogenic global warming due to increases in atmospheric greenhouse gases concentrations. In this study, biogeophysical impacts on LST were quantified based on analytic evaluation and model simulations. The findings indicated a cooling effect of −2.1 × 10−2 K day−1 and −2.8 × 10−2 K day−1 due to the advanced start of growing season and delayed end of growing season, respectively. These cooling effects are mostly caused by an enhancement in turbulent heat transfer from land to atmosphere through a decrease in aerodynamic resistance. Our results suggest reasons for the biogeophysical cooling effect of the lengthened growing season, which is important for projecting seasonal climate change. Key Points: Biogeophysical impact of changes in vegetation phenology on land surface temperature over northern deciduous forest is examinedAdvance start of growing season and delayed end of growing season both induce land surface coolingThe mechanism responsible for surface cooling is enhanced turbulent heat transfer by a decrease in aerodynamic resistance [ABSTRACT FROM AUTHOR]

The increase in global carbon emissions has intensified the effects of CO2 fertilization on the carbon cycle. CO2 fertilization is shaped by several factors, including the physiological differences among trees of varied forest ages and types, as well as the influence of different climatic conditions. It is essential to investigate the differences in CO2 fertilization effects across diverse climate zones and delve into the association between these effects and forest age and type. Such exploration will deepen our knowledge of forest responses to environmental changes. This study used annual ring width data from the International Tree-Ring Data Bank, employing the generalized additive mixed models and the Random Forest model to discern the pattern of the CO2 fertilization effect concerning forest age in the Northern Hemisphere. This study also explored the variations in the effect of CO2 fertilization across unique climate zones and the disparities among various forest types within the same climatic zone. The results indicated a link between forest age and the CO2 fertilization effect: it tends to increase in sapling forests and middle-aged forests and diminish in mature forests. Warmer, drier environments had a more marked effect of increased CO2 on tree fertilization. Additionally, coniferous forests demonstrated a more substantial CO2 fertilization effect than broadleaf forests, and deciduous needle-leaf forests surpassed evergreen needle-leaf forests in this regard. This research is pivotal in understanding the shifting patterns of CO2 fertilization effects and how forests respond to atmospheric changes. [ABSTRACT FROM AUTHOR]

Wind in the free atmosphere is one of the processes recommended by the World Meteorological Organization for climate monitoring. An analysis of the wind regime on large spatial scales presents specific difficulties, since both the vertical and horizontal distributions of wind speed are highly variable. In order to have an idea about the general characteristics of the wind regime in the main atmospheric layers, the Russian Institute of Hydrometeorological Information, World Data Center (RIHMI-WDC), developed a method for monitoring the wind regime of the free atmosphere over the territory of the Russian Federation. The goal of this article is to further develop these works both in relation to the region and in terms of research fields. The article presents the results of monitoring the wind speed in the free atmosphere not only over the territory of Russia, but also over the entire Northern Hemisphere, compares the results of radio sounding data and the ERA5 fifth-generation reanalysis data, and it also considers trends in variability of the wind regime over the period 1985–2018. An analysis of wind characteristics in the troposphere and lower stratosphere of the Northern Hemisphere has been carried out in accordance with the technique developed earlier for monitoring the wind regime of wind speed in the free atmosphere. The analysis was extended to the entire Northern Hemisphere using two data sources: an array of long-term radiosonde measurements performed at Russian Institute of Hydrometeorological Information, World Data Center (RIHMI-WDC) and fifth-generation ERA5 reanalysis. The monitoring results based on the two data sources are qualitatively and quantitatively consistent with each other in the areas covered by the network of aerological stations, except for individual high-mountain regions. The distribution of long-term averages in general terms coincides with the distribution of wind speed based on earlier studies. At the same time, each year is distinguished by its own characteristics, displacements of zones of weak and strong winds, and their intensity. Variability trends over the period 1985–2018 in different regions of the Northern Hemisphere were oppositely directed. The strongest negative wind speed trends reaching –1.5 m s–1 over 10 years occurred in the lower stratosphere north of 55°–60° N. This may indicate a weakening of the winter west–east transport in this region. In the latitudinal belt 30°–45° N over the Eurasian region, on the contrary, positive trends reaching 1.1 m s–1 over 10 years have been observed. [ABSTRACT FROM AUTHOR]

The maximum latewood density (MXD) of tree rings can reflect the temperature of the growing season, but the timing of the response differs among regions. We selected 152 maximum latewood density chronologies from the Northern Hemisphere that showed a significant response to temperature. Based on a cluster analysis and the sensitivity of MXD to the monthly mean temperature, the chronologies were classified into six clusters. The clusters showed distinct regional characteristics, and the period and peak month of significant response of the chronologies in each cluster to temperature were different. Spatial synchronization of the MXDs revealed that the two clusters distributed in Europe showed the most consistency and the strongest response to the April–September monthly mean temperature compared with the other clusters. Temperature accounted for more than 40% of the total MXD variance in all clusters, whereas the effect of precipitation was much smaller. In addition to climatic factors, the random effect of the latitude and longitude of sampling sites, elevation, and tree species was a major factor contributing to the variance in MXD in each cluster. Latitude and longitude had the strongest influence among the three random effects, and tree species had the weakest influence, except at high latitudes. The MXD of each cluster showed sensitivity to temperature within a certain interval, with a positive linear response, and the sensitivity interval was greatest at high latitudes. Certain clusters showed a negative linear sensitivity to precipitation. The results provide a reference for studying the climatic threshold of large-scale tree-ring density formation. [ABSTRACT FROM AUTHOR]

Extratropical cyclones (ETCs) are a common source of natural hazards, from heavy rain to high winds, and the direction and speed of ETC propagation influence where impacts occur and for how long. Eighteen models from phase 6 of the Coupled Model Intercomparison Project (CMIP6) are used to examine the response of Northern Hemisphere ETC propagation to global warming. In winter, simulations show that ETCs become slower over North America and the Arctic but faster over the Pacific Ocean and part of Europe. In summer, storm propagation becomes slightly slower throughout much of the midlatitudes (308-608N). Trends in both seasons relate closely to the impact of global warming on upper-level (250 hPa) winds and the 850-250-hPa thickness gradient. Wherever local thickness gradients weaken in the future, ETCs travel more slowly; conversely, wherever they strengthen, ETCs travel more quickly. In contrast to past work, we find that winter storm propagation becomes more zonal over the Pacific and Atlantic Oceans, which may link to decreased atmospheric blocking and less-sinuous flow at 500 hPa. The importance of model projections of the 850-250-hPa thickness gradient for meridionality of ETC propagation remains uncertain for these regions. However, for North America, models that project stronger thickness gradients also project less-sinuous flow and more-zonal ETC propagation. Overall, this work highlights strong regional variation in how the speed and direction of ETC propagation, and the upper-level circulation patterns that govern them, respond to continued warming. [ABSTRACT FROM AUTHOR]

The central role of tropical sea surface temperature (SST) variability in modulating Northern Hemisphere (NH) extratropical climate has long been known. However, the prevailing pathways of teleconnections in observations and the ability of climate models to replicate these observed linkages remain elusive. Here, we apply maximum covariance analysis between atmospheric circulation and tropical SST to reveal two coexisting tropical-extratropical teleconnections albeit with distinctive spatiotemporal characteristics. The first mode, resembling the Pacific-North American (PNA) pattern, favors a tropical-Arctic in-phase (warm Pacific-warm Arctic) teleconnection in boreal spring and winter. However, the second mode, with a slight seasonal preference of summer, is manifested as an elongated Rossby wave train emanating from the tropical eastern Pacific that features an out-of-phase relationship (cold Pacific-warm Arctic) between tropical central Pacific SSTs and temperature variability over the Arctic (referred to as the PARC mode). While climate models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6) appear to successfully simulate the PNA mode and its temporal characteristics, the majority of models' skill in reproducing the PARC mode is obstructed to some extent by biases in simulating low-frequency SST and rainfall variability over the tropical eastern Pacific and the climatological mean flow over the North Pacific during boreal summer. Considering the contribution of the PARC mode in shaping low-frequency climate variations over the past 42 years from the tropics to the Arctic, improving models' capability to capture the PARC mode is essential to reduce uncertainties associated with decadal prediction and climate change projection over the NH. [ABSTRACT FROM AUTHOR]

With a pair of high‐resolution (HR, 10 km ocean and 25 km atm) and low‐resolution (LR, 100 km ocean and 100 km atm) Community Earth System Model (CESM) simulations, we investigate and compare the long‐term mean Northern Hemisphere (NH) wintertime storm tracks against reanalysis data. Based on several Eulerian measures, the CESM‐HR shows a poleward shift of the NH storm tracks and a reduced equatorward bias in the North Pacific relative to the CESM‐LR. Those may be associated with the refined topography of the Tibetan Plateau as well as the improved subtropical jet, stationary planetary waves, atmospheric baroclinity, and baroclinic energy conversion over the North Pacific. We also find that sharper oceanic fronts along the Kuroshio Extension accompanied by enhanced local atmospheric baroclinity and strengthened eddy heat flux over the northern North Pacific could be related to those improvements. Nevertheless, the North Atlantic storm track in HR is placed too north, leading to a larger negative bias over the subtropical zone than in LR. The simulated insufficient subtropical sensible and latent heat fluxes and northward zonal winds in HR seemingly coincide with the deficits in the North Atlantic storm track. The stronger NH branch of the Hadley cell and its poleward expansion in HR may be linked to the changes in the tropical precipitation and the poleward shift of the NH storm tracks. Further studies of attributing these biases to a specific aspect of the climate model by sensitivity experiments are warranted for further clarification of the mechanisms. Plain Language Summary: Storm tracks refer to the preferred travel paths of extratropical cyclones and anticyclones, which contribute to precipitation and wind extremes in midlatitudes. So, accurately representing storm tracks is crucial for climate models. This study compares and evaluates the long‐term mean Northern Hemisphere (NH) wintertime storm tracks in a pair of high‐resolution (HR) and low‐resolution (LR) climate model simulations against observations. HR shows a poleward shift of the NH storm tracks, leading to some improvements in the North Pacific relative to LR. The refined Tibetan Plateau and sea surface temperature may play a role in the improved North Pacific storm track by altering atmospheric circulations and air‐sea interactions. Nevertheless, the North Atlantic storm track is placed too north in HR, leading to a larger negative bias over the subtropical zone. The weakened upward heat and moisture fluxes and northward zonal winds are related to the deficits in the North Atlantic storm track simulation. The stronger Hadley cell and its poleward expansion in HR also show associations with the poleward shift of the NH storm tracks. This study discusses how model horizontal resolution affects the simulated NH storm tracks, which may provide a reference for the development of future high‐resolution climate models. Key Points: High‐resolution CESM shows a poleward shift of storm tracks and reduced biases in the North Pacific compared to the low‐resolutionRefined Tibetan Plateau topography and improved SST are related to the better simulated North Pacific storm track by altering baroclinityBetter represented sensible and latent heat flux and zonal wind can be crucial for improving the North Atlantic storm track simulation [ABSTRACT FROM AUTHOR]

Despite the crucial role of moist diabatic processes in mid-latitude storm tracks and related model biases, we still lack a more complete theoretical understanding of how diabatic processes affect the evolution of storm tracks. To alleviate this shortcoming, we investigate the role of diabatic processes in the evolution of the northern hemispheric storm tracks using a framework based on the tendency of the slope of isentropic surfaces as a measure of baroclinic development. We identify opposing behaviours in the near-surface and free troposphere for the relationship between the flattening of the slope of isentropic surfaces and its restoration by diabatic processes. Near the surface (900–825 hPa), cold air advection associated with cold air outbreaks initially acts to flatten isentropic surfaces, with air–sea interactions ensuing to restore surface baroclinicity. In the free troposphere (750–350 hPa), on the other hand, the diabatic generation of the slope of isentropic surfaces precedes its depletion due to tilting by eddies, suggesting the primary importance of moist diabatic processes in triggering subsequent baroclinic development. The same phasing between diabatic and tilting tendencies of the slope is observed both in upstream and downstream sectors of the North Atlantic and North Pacific storm tracks. This suggests that the reversed behaviour between near-surface and free troposphere is a general feature of mid-latitude storm tracks. In addition, we find a correspondence between the diabatic generation of the slope of isentropic surfaces and enhanced precipitation as well as moisture availability, further underlining the crucial role of moisture and moist processes in the self-maintenance of storm tracks. [ABSTRACT FROM AUTHOR]

We quantified the seasonal/regional patterns and changes in cyclone activity in the atmosphere of the Northern Hemisphere and determined the contribution of extratropical cyclones to the formation of corresponding patterns and precipitation changes. It is ascertained that the contribution of extratropical cyclones to the total amount of precipitation exceeds 60% on the whole; for regions with a high cyclone frequency, it attains 75% in winter and 65% in summer. Intense cyclones contribute the most: 60% in winter and 35% in summer. [ABSTRACT FROM AUTHOR]

Abstract Concurrent heat extremes (CHEs) are becoming increasingly common in the mid‐high latitudes across the Northern Hemisphere (NH), underscoring the need to comprehend their spatiotemporal characteristics and underlying causes. Here we reveal a phase‐locking behavior in Wave‐4 pattern, particularly after mid‐1990s, giving rise to a prominent CHE mode akin to heat extreme pattern observed in 2022, which swept most NH regions. Wave‐4 pattern significantly amplifies the likelihood of CHEs in Eastern Europe (∼30%), Northeast Asia (∼25%), and northwestern coast of North America (∼15%), while reducing the likelihood in central North America and northern Central Asia. During 1979–2022, the identified pattern accounted for over 69.7% of the trends in heat extremes over the mid‐high latitudes of the NH, directly exposing approximately 333.5 million people to heat extremes. Observations and simulations indicate that radiation anomalies over Eastern European Plain and West Siberian Plain play pivotal roles as primary forcing sources for Wave‐4 pattern.

Technological and methodological advances in biogeography, phylogenetics, and bioinformatics during the past couple of decades provide greatly enhanced insights into the evolutionary history of birds in space and time. Molecular data, especially next-generation DNA sequencing, have produced a revolution in reconstructing the phylogenetic history of lineages. These advances shed a new light on the mode, tempo, and spatial context of differentiation processes that shaped the composition and structure of extant forest bird communities of temperate forests of the Northern Hemisphere. This paper offers a framework for understanding this history based on analytical tools that allow us to decipher the imprint of changes in the geographic configuration of land masses and in climates since the Mesozoic, with a focus on the temperate-tropical flyways that connect the massive forest blocks of the Northern to those of the Southern Hemispheres. Differentiation of most extant bird lineages and species has been shown to have begun in a deeper past than formerly thought, although recent analyses from molecular phylogenies also support the much-debated Late Pleistocene model of speciation. Geographical connections between tropical and temperate realms make north-south flyways important drivers of differentiation for many lineages. The histories of differentiation and colonisation of clades, including both resident and long-distance migrants, are discussed in relation to two alternative theories, the ‘southern home theory’ and the ‘northern home theory’. The region-specific characters of the bird faunas and differences between the main temperate forest blocks of the Northern Hemisphere are discussed in light of the hypotheses concerning dispersal processes related with geographical configuration of land masses. Differential dispersal-colonisation rates from tropical regions and subsequent diversification in temperate regions (and vice versa) are also considered. The causes of the observed decline in diversification rates during the Pleistocene are examined from phylogenetic reconstructions of various clades.

The vegetation patterns in high-latitude and high-altitude regions (HLAR) of the Northern Hemisphere are undergoing significant changes due to the combined effects of global warming and human activities, leading to increased uncertainties in vegetation phenological assessment. However, previous studies on vegetation phenological changes often relied on long-term time series of remote sensing products for evaluation and lacked comprehensive analysis of driving factors. In this study, we utilized high temporal resolution seamless MODIS products (MODIS-NDVISDC and MODIS-EVI2SDC) to assess the vegetation phenological changes in High-Latitude-Altitude Regions (HLAR) of the Northern Hemisphere. We quantified the differences in vegetation phenology among different land-use types and determined the main driving factors behind vegetation phenological changes. The results showed that the length of the growing season (LOS) derived from MODIS-NDVISDC was 8.9 days longer than that derived from MODIS-EVI2SDC, with an earlier start of the growing season (SOS) by 1.5 days and a later end of the growing season (EOS) by 7.4 days. Among different vegetation types, deciduous needleleaf forests exhibited the fastest LOS extension (p < 0.01), while croplands showed the fastest LOS reduction (p < 0.05). Regarding land-use transitions, the conversion of built-up land to forest and grassland had the longest LOS. In expanding agricultural areas, the LOS of land converted from built-up land to cropland was significantly higher than that of other land conversions. We analyzed human activities and found that as the human footprint gradient increased, the LOS showed a decreasing trend. Among the climate-related factors, the dominant response of phenology to temperature was the strongest in the vegetation greening period. During the vegetation browning period, the temperature control was weakened, and the control of radiation and precipitation was enhanced, accounting for 20–30% of the area, respectively. Finally, we supplement and prove that the highest contributions to vegetation greening in the Northern Hemisphere occurred during the SOS period (May–June) and the EOS period (October). Our study provides a theoretical basis for vegetation phenological assessment under global change. It also offers new insights for land resource management and planning in high-latitude and high-altitude regions.

Since the Paris Agreement, climate policy has focused on 1.5° and 2°C maximum global warming targets. However, the agreement lacks a formal definition of the nineteenth-century "pre-industrial" temperature baseline for these targets. If global warming is estimated with respect to the 1850–1900 mean, as in the latest IPCC reports, uncertainty in early instrumental temperatures affects the quantification of total warming. Here, we analyze gridded datasets of instrumental observations together with large-scale climate reconstructions from tree rings to evaluate nineteenth-century baseline temperatures. From 1851 to 1900 warm season temperatures of the Northern Hemisphere extratropical landmasses were 0.20°C cooler than the twentieth-century mean, with a range of 0.14°–0.26°C among three instrumental datasets. At the same time, proxy-based temperature reconstructions show on average 0.39°C colder conditions with a range of 0.19°–0.55°C among six records. We show that anomalously low reconstructed temperatures at high latitudes are underrepresented in the instrumental fields, likely due to the lack of station records in these remote regions. The nineteenth-century offset between warmer instrumental and colder reconstructed temperatures is reduced by one-third if spatial coverage is reduced to those grid cells that overlap between the different temperature fields. The instrumental dataset from Berkeley Earth shows the smallest offset to the reconstructions indicating that additional stations included in this product, due to more liberal data selection, lead to cooler baseline temperatures. The limited early instrumental records and comparison with reconstructions suggest an overestimation of nineteenth-century temperatures, which in turn further reduces the probability of achieving the Paris targets. Significance Statement: The warming targets formulated in the Paris Agreement use a "pre-industrial" temperature baseline that is affected by significant uncertainty in the instrumental temperature record. During the second half of the nineteenth century, much of the continental landmasses were not yet covered by the observational station network and existing records were often subject to inhomogeneities and biases, thus resulting in uncertainty regarding the large-scale mean temperature estimate. By analyzing summer temperature reconstructions from tree-rings for the Northern Hemisphere extratropical land areas, we examine an independent climate archive with a typically broader and more continuous spatial extent during the "pre-industrial" period. Despite the additional uncertainty when using climate reconstructions instead of direct observations, there is evidence for an overestimation of land temperature during the summer season in early instrumental data. Colder early instrumental temperatures would reduce the probability of reaching the Paris targets. [ABSTRACT FROM AUTHOR]

Assessment of spring snow cover fraction (SCF) can be valuable for understanding the efficacy of certain Earth system models (ESMs) in simulating the energy exchange between land and atmosphere system, global hydrological cycle and future climate impacts. Here, we provide a comprehensive evaluation of simulated spring SCF from 23 and 20 ESMs participating CMIP5 and CMIP6, against satellite data from National Oceanic and Atmospheric Administration and National Climatic Data Center (NOAA/NCDC) and a long‐term Northern Hemisphere daily 5‐km snow cover extent product (JASMES) over the Northern Hemisphere (NH) and its 13 subregions during the period of 1982–2005 and 2072–2095. Our results show that (a) no model performs consistently better in simulating spring SCF from all aspects (mean annual, long‐term trend and climatological monthly of spring SCF); (b) the mean annual of spring SCF that was simulated by CMIP5 and CMIP6 model simulations was underestimated in most of the NH and overestimated over the Tibetan Plateau and eastern Asia; (c) most of the model simulations showed a stronger reduction trend for mean annual of spring SCF; (d) the climatological monthly variation of spring SCF is reasonably captured by all model simulations, except for overestimation over the TIB and EAS regions, and there is underestimation in other regions; (e) compared to CMIP5, most of the model simulations in CMIP6 exhibit an improved ability to simulate spring SCF across all aspects; (f) we confirm that the multi‐model ensemble mean (MME) is a better way to represent the three aspects of spring SCF than most individual model simulations. Finally, the spring SCF values predicted by models with better simulation abilities over the NH and its 13 subregions under different scenarios show decreasing trends. Specifically, the highest decreasing trend of spring SCF was found under high emission scenarios (RCP8.5 and SSP5‐8.5). [ABSTRACT FROM AUTHOR]

The thermal structure of the troposphere remains a hot topic, including modelling issues as well as temperature field simulations. This study evaluates the relationship between the air temperature at the Earth's surface and the temperature of various layers of the troposphere over the Northern Hemisphere, as well as attempts to identify determinants of its variability. Vertical differentiation has been analyzed from the layer σ = 0.995 representing the surface (surface air temperature, SAT), up to an isobaric level of 300 hPa with a focus on the main pressure levels, i.e., 925 hPa, 850 hPa, 700 hPa, 500 hPa. The data were obtained from an NCEP/NCAR reanalysis with a resolution of 2.5 degrees latitude and longitude for the period 1961–2020. The relationship between the SAT and the temperature at each level was expressed using a simple but effective correlation coefficient by Pearson (PCC). These relationships obviously, according to Tobler's law, weaken with an increasing altitude. However, the distribution of PCC (both horizontal and vertical) proves the impact of geographic factors associated with the relief and also with the surface itself (e.g., land cover). These factors are the main drivers of inversion layers and significantly disturb the straight vertical structure of the atmosphere. The research has shown a significant interannual differentiation of these interactions, as well as their spatial diversity in geographic space. The altitude–temperature relationship becomes weaker in all seasons, but much faster during summer and winter, relative to both spring and autumn. [ABSTRACT FROM AUTHOR]

Sudden stratospheric warmings (SSWs) are extreme disruptions of the wintertime polar vortex that can alter the tropospheric weather for over 2 months. However, the reasons why only some SSWs have a tropospheric impact are not yet clear. This study analyses the tropospheric impact of SSWs over the Atlantic region as measured by the latitudinal displacement of the North Atlantic eddy-driven jet following SSWs. We use reanalysis data for the period 1950–2020 to examine differences in the stratospheric and tropospheric circulation for SSWs with an equatorward (EQ) or a poleward (POLE) shift. Our results show a stronger and more persistent Northern Annular Mode (NAM) signal in the lower stratosphere for EQ than for POLE, beginning 2 weeks before the onset date. In the troposphere, we find precursory signals of the Atlantic jet behavior over Siberia, consistent with previous studies, and also over the central North Pacific and central Europe. In particular, our results suggest that the noncanonical poleward jet shift response to SSWs is in part modulated by circulation anomalies over the central North Pacific, and that these are in turn connected to the cold phase of El Niño–Southern Oscillation. Further analysis of the enhanced predictability given by these precursors suggests that the sign of the lower-stratospheric NAM and the geopotential anomalies over the central North Pacific significantly affect the probability of having an EQ or POLE response of the Atlantic jet. [ABSTRACT FROM AUTHOR]

The Northern Hemisphere snow-cover (NHSC) interannual variability can serve as a crucial source of climate predictability. However, the spatiotemporal characteristics of the NHSC interannual variability and associated formation mechanism lack a thorough investigation using the latest reliable datasets. In this observationally based study, we identify the leading mode of the wintertime NHSC interannual variability and reveal the major determinants and mechanisms for forming the mode. Results show that the leading mode exhibits a hemispheric dipole pattern characterized by snow-cover anomalies in the central-eastern United States and Europe, contrary to those in the Tibetan Plateau (TP). Importantly, the leading mode of TP-only snow-cover variability is essentially a regional manifestation of the dipole NHSC anomaly pattern. The wintertime hemispheric atmospheric circulation anomaly mode, that is, the Arctic Oscillation (AO), primarily determines the dipole NHSC anomaly pattern via altering snowfall and snowmelt. During a positive phase of AO, an anomalous atmospheric anticyclone over the midlatitude North Atlantic favors increased warm-air advection over the central-eastern United States and Europe, reducing the snowfall and the snow cover there. Meanwhile, the anomalously warm atmospheric thermal condition in Europe accompanied by enhanced westerly moisture flux convergence tends to heat the underlying land surface via reducing upward sensible heat flux and increasing downward longwave radiation, thereby causing increased snowmelt and decreased snow cover in northeastern Europe. Associated with the aforementioned atmospheric circulation anomalies, an anomalous atmospheric cyclone prevailing over the TP tends to cause increased southeasterly moisture flux convergence, favoring snowfall and snow increase in the TP. [ABSTRACT FROM AUTHOR]

We have obtained quantitative estimates of seasonal and regional features and changes in cyclone activity in the atmosphere of the Northern Hemisphere and determined the contribution of extratropical cyclones to the formation of corresponding features and changes in the surface wind using ERA5 reanalysis data for recent decades (1979–2021). According to these estimates, the contribution of extratropical cyclones to surface wind speeds in the regions of their high occurrence reaches 60% in winter and 50% in summer. The strongest contribution is related to intense cyclones: about 60% in winter and about 25% in summer. [ABSTRACT FROM AUTHOR]

Abstract With a pair of high‐resolution (HR, 10 km ocean and 25 km atm) and low‐resolution (LR, 100 km ocean and 100 km atm) Community Earth System Model (CESM) simulations, we investigate and compare the long‐term mean Northern Hemisphere (NH) wintertime storm tracks against reanalysis data. Based on several Eulerian measures, the CESM‐HR shows a poleward shift of the NH storm tracks and a reduced equatorward bias in the North Pacific relative to the CESM‐LR. Those may be associated with the refined topography of the Tibetan Plateau as well as the improved subtropical jet, stationary planetary waves, atmospheric baroclinity, and baroclinic energy conversion over the North Pacific. We also find that sharper oceanic fronts along the Kuroshio Extension accompanied by enhanced local atmospheric baroclinity and strengthened eddy heat flux over the northern North Pacific could be related to those improvements. Nevertheless, the North Atlantic storm track in HR is placed too north, leading to a larger negative bias over the subtropical zone than in LR. The simulated insufficient subtropical sensible and latent heat fluxes and northward zonal winds in HR seemingly coincide with the deficits in the North Atlantic storm track. The stronger NH branch of the Hadley cell and its poleward expansion in HR may be linked to the changes in the tropical precipitation and the poleward shift of the NH storm tracks. Further studies of attributing these biases to a specific aspect of the climate model by sensitivity experiments are warranted for further clarification of the mechanisms.

Growth and senescence rates are critical ecological indicators of seasonality shifts of vegetation, with both sensitive to climate change. Here we investigated daily mean vegetation growth and senescence rates, and the major climate forcing across the Northern Hemisphere (>30°N) using satellite-derived normalized difference vegetation index (NDVI) and flux-based gross primary productivity (GPP) from 1982 through 2015. Both growth and senescence rates are higher at high latitudes than those at low latitudes, with spatially-averaged values increased by 1.0 × 10−4 and 0.7 × 10−4 NDVI-units·day−1 per degree latitude. These increases were greater in Eurasia than in North America. A parallel acceleration of growth (0.8 ×10−4 NDVI-units·day−1·decade−1) and senescence (0.6 ×10−4 NDVI-units·day−1·decade−1) rates was found for the 34-year study period. The warming-induced increases in vegetation peak growth (peak NDVI) contributed strongly to this parallel acceleration, while unequal advances or delays of three key phenological indicators (the start (SOS), peak (POS), and end (EOS) of the growing season) exerted influential effects on the rates. However, no single climatic factor during any period appeared responsible for the variations in growth and senescence rates. In areas with growth and senescence rates that are determined by peak growth, temperature and precipitation during the growth period accelerated both rates through elevating peak growth. On the other hand, in areas with growth rate determined by SOS, rising temperature before SOS decelerated the growth rate by advancing SOS. In areas with senescence rate determined by EOS, both temperature and radiation during the senescence period contributed to changes in senescence rate by influencing EOS. In sum, a central focus should be placed on the linkages among climate, phenology, and growth and senescence rates for quantifying vegetation seasonality and associated ecosystem function under the changing climate.

How future multiple tropical cyclone events (MTCEs) could change is crucial for effective risk management and ensuring human safety, however, it remains unclear. This study projects changes in MTCEs by 2050 in the major basins of the Northern Hemisphere using high‐resolution climate models. Results show a significant increase in the frequency and duration of MTCEs over the North Atlantic (NA), a notable decrease over the western North Pacific (WNP), and little change over the eastern North Pacific (ENP). The increase in MTCEs over the NA is concentrated in August–September, while the decrease over the WNP occurs in most months. In contrast, the ENP exhibits large yet insignificant seasonal variation, suggesting considerable uncertainty in this basin. Further analysis shows that mid‐level vertical motion dominates the MTCE changes over the WNP, while vertical wind shear contributes the most to the NA, which may be linked to future changes in tropical convection. Plain Language Summary: Multiple tropical cyclone (TC) events (MTCEs), that is two or more TCs simultaneously occurring in the same basin, pose great risks to human society. This study projects future changes in the MTCEs by 2050, showing a significant increase over the North Atlantic (NA) while a robust reduction over the western North Pacific (WNP). The future MTCEs over the eastern North Pacific (ENP) show little change relative to the present climate. The increase of MTCEs over the NA is concentrated in August–September, while the decrease over the WNP occurs nearly from April to November. In contrast, there is large yet insignificant seasonal variation over the ENP, which could lead to little change in annual MTCEs. Furthermore, these changes are primarily attributed to the changes in local large‐scale dynamic conditions associated with tropical convection in future decades. Key Points: The projection of future multiple tropical cyclone events (MTCEs) shows a decline in the western North Pacific (WNP) but a significant increase in the North Atlantic (NA)The mid‐level vertical motion dominates the MTCE changes over the WNP, while vertical wind shear is important for the NAFuture monthly MTCEs show large yet insignificant seasonal variation over the eastern North Pacific, causing little trend in annual MTCEs [ABSTRACT FROM AUTHOR]

The four-dimensional characteristics of precipitation and latent heating associated with Northern Hemisphere winter extratropical cyclones (ETCs) are quantitatively analyzed using over 1000 ETCs observed by the Ku-band radar on board the Global Precipitation Measurement (GPM) Core Observatory. We find that the maximum precipitation amount is observed before the minimum central pressure of ETCs (developing stage), independent of the deepening ratio. A key finding is that a cyclone in the developing stage has two large precipitation areas with contrasting precipitation characteristics. One is observed on the forward-left side of ETCs, collocating with warm fronts (Area X). The other is identified on the right-hand side of the ETC center in association with the warm sector and cold fronts (Area Y). These areas become unclear in the mature stage and disappear in the decaying stage. Many stratiform precipitation pixels weaker than 5 mm h−1 compose the large precipitation amount in Area X, with a stratiform-to-total precipitation ratio of more than 90%. In contrast, intense convective precipitation pixels of over 20 mm h−1 are observed about 3 times more in Area Y than in Area X, resulting in a stratiform-to-total precipitation ratio of 65%–80%. The most intense precipitation around ETCs is observed in this area. A larger latent heating maximum at 3.5-km altitude and a higher near-surface cooling rate in Area X result in a higher vertical heating gradient compared to Area Y. The contrasting characteristics between the two areas are more pronounced in the rapidly developing ETCs. Significance Statement Statistical analyses are conducted to elucidate the four-dimensional structures of precipitation and latent heating associated with more than 1000 Northern Hemisphere winter extratropical cyclones using data observed by the Ku-band radar on board the Global Precipitation Measurement (GPM) Core Observatory. The horizontal precipitation composite at the developing stage of the cyclones shows two areas with large precipitation amounts. One is characterized by a large amount of weak stratiform precipitation, and a higher vertical heating gradient, collocating with warm fronts. The other is characterized by intense convective precipitation in association with the warm sector and cold fronts. The quantitative information on precipitation and latent heating obtained from the observation of many cyclones is valuable for the validation of numerical simulation results. [ABSTRACT FROM AUTHOR]

Forests are increasingly exposed to extreme global warming‐induced climatic events. However, the immediate and carry‐over effects of extreme events on forests are still poorly understood. Gross primary productivity (GPP) capacity is regarded as a good proxy of the ecosystem's functional stability, reflecting its physiological response to its surroundings. Using eddy covariance data from 34 forest sites in the Northern Hemisphere, we analyzed the immediate and carry‐over effects of late‐spring frost (LSF) and growing season drought on needle‐leaf and broadleaf forests. Path analysis was applied to reveal the plausible reasons behind the varied responses of forests to extreme events. The results show that LSF had clear immediate effects on the GPP capacity of both needle‐leaf and broadleaf forests. However, GPP capacity in needle‐leaf forests was more sensitive to drought than in broadleaf forests. There was no interaction between LSF and drought in either needle‐leaf or broadleaf forests. Drought effects were still visible when LSF and drought coexisted in needle‐leaf forests. Path analysis further showed that the response of GPP capacity to drought differed between needle‐leaf and broadleaf forests, mainly due to the difference in the sensitivity of canopy conductance. Moreover, LSF had a more severe and long‐lasting carry‐over effect on forests than drought. These results enrich our understanding of the mechanisms of forest response to extreme events across forest types. [ABSTRACT FROM AUTHOR]

Introduction/Background Seasonal trends in atopic dermatitis (AD)-related healthcare visits vary by geographical location and climate. Changes in temperature, moisture, and allergens contribute to disease fluctuation activities throughout the year. The global, placebo-controlled, 1-year LIBERTY AD CHRONOS study (NCT02260986) offers the opportunity to evaluate AD seasonality and the impact of dupilumab on moderate-to-severe AD in adults regardless of season. Objectives To identify seasonal trends in patient-reported AD severity and frequency of symptoms, and to report the effect of dupilumab treatment in adults with moderate-to-severe AD across seasons. Methods CHRONOS was a randomized, double-blind, phase 3 trial of adults with moderate-to-severe AD.1 Patients were treated with dupilumab 300 mg every week (qw), every two weeks (q2w), or placebo qw, all with concomitant topical corticosteroids (TCS). In this post hoc analysis, the proportion of patients per severity category of Patient-Oriented Eczema Measure (POEM) score (range 0–28) by month was compared between patients receiving dupilumab 300 mg q2w + TCS (n = 79) or placebo qw + TCS (n = 234) for 1 year across 10 countries in the Northern Hemisphere. Improvement in AD was determined as an increase in proportion of patients with mild and clear POEM scores (≤7). Meteorological seasons were defined as winter (December 1 – February 28/29), spring (March 1 – May 31), summer (June 1 – August 31), and fall (September 1 – November 30). Sensitivity analyses confirmed that season of enrollment was balanced across treatment arms and disease seasonality was independent of treatment length. P values are based on Chi-Square tests or Monte Carlo simulations of the Exact Test, based on sample size. All P values are nominal, and no adjustments have been made for multiple testing. Data are presented as observed. Results The proportion of patients in both treatment arms with mild and clear POEM scores (≤7) was lowest in spring months (March: 13% vs 24%; April: 10% vs 23%; May: 20% vs 44%; placebo vs dupilumab). The proportion of patients with mild and clear POEM scores was increased through summer (June: 21% vs 54%; July: 24% vs 58%; August: 29% vs 53%; placebo vs dupilumab) and fall (September: 27% vs 62%; October: 23% vs 58%; November: 21% vs 63%; placebo vs dupilumab), before beginning to decline in winter (December: 21% vs 56%; January: 16% vs 46%; February: 15% vs 41%; placebo vs dupilumab). Overall, POEM scores indicated significantly better outcomes for patients receiving dupilumab treatment vs placebo throughout the year (overall P < 0.01 for all 12 months). Conclusions Across the Northern Hemisphere, patient-reported disease severity in adults with moderate-to-severe AD was greatest in the spring months. Adults with moderate-to-severe AD receiving dupilumab treatment reported improvement in frequency of disease symptoms across all seasons compared to patients receiving placebo treatment. [ABSTRACT FROM AUTHOR]

The analysis of spatial and temporal variability in the number of non-Gaussian extreme anomalies of climatic parameters was carried out for both the initial time series and synoptic variability in the troposphere of the Northern Hemisphere over the period 1979–2018, based on ERA-Interim reanalysis data. There are predominantly three types of empirical distribution densities at 850 hPa, each characterizing the processes of advective and convective heat transfer. At the beginning of the 21st century, compared to the end of the 20th century, there was an increase in the number of anomalies in vertical wind speed and specific humidity for the Northern Hemisphere. Additionally, there is an increase in the number of zonal wind speed anomalies in the low and middle latitudes. Regions with the maximum number of anomalies are primarily located over the continents, while for vertical wind speed anomalies, they are predominantly over the oceans. The application of R/S analysis and multifractal analysis has established that the identified tendencies (which are persistent processes) will continue in the identified regions. The time series of non-Gaussian anomalies (both initial and synoptic scales) exhibit a long-term memory of approximately four years, and synoptic extreme anomalies were found to be more predictable.

Abstract How future multiple tropical cyclone events (MTCEs) could change is crucial for effective risk management and ensuring human safety, however, it remains unclear. This study projects changes in MTCEs by 2050 in the major basins of the Northern Hemisphere using high‐resolution climate models. Results show a significant increase in the frequency and duration of MTCEs over the North Atlantic (NA), a notable decrease over the western North Pacific (WNP), and little change over the eastern North Pacific (ENP). The increase in MTCEs over the NA is concentrated in August–September, while the decrease over the WNP occurs in most months. In contrast, the ENP exhibits large yet insignificant seasonal variation, suggesting considerable uncertainty in this basin. Further analysis shows that mid‐level vertical motion dominates the MTCE changes over the WNP, while vertical wind shear contributes the most to the NA, which may be linked to future changes in tropical convection.

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The start of the growing season (SOS) is essential to track the responses of vegetation to climate change. However, recent findings on whether the SOS in the middle‐high latitudes of the Northern Hemisphere (NH) continued to advance or reversed during the global warming hiatus were not consistent. It is necessary to investigate the causes of this controversy and to examine the relationship between the SOS and preseason temperature trends. To this end, we first applied four widely used phenology extraction methods to derive the SOS from the GIMMS NDVI3g dataset and then used the ensemble empirical modal decomposition (EEMD) method to extract the nonlinear trends of the SOS and preseason temperature. Our results clarify, for the first time, that the limitations of the linear assumption‐based trend analysis methods are an important but overlooked cause of the discrepancies among existing studies on whether the SOS was advanced or delayed in the NH (>30° N) during the global warming hiatus. We further revealed the range of the mismatches between the SOS and preseason temperature trends at the latitude, altitude and biome levels. Specifically, we discovered that the SOS in the NH (>30° N) obtained by the four phenology extraction methods showed a significant reversal from advance to delay during the global warming hiatus, and the corresponding average rate of change was very small. The area showing increasing preseason temperatures decreased during the global warming hiatus, but it always occupied most of the NH (>30° N). However, delayed SOS trends were dominant in the NH from 50° N to 60° N, above 3000 m and in biomes other than TBMF and BF. Accordingly, using an EEMD‐like approach to evaluate the changes in the SOS and preseason temperature is necessary for improving our understanding of the changes in the SOS and their association with climate. [ABSTRACT FROM AUTHOR]