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Detection and attribution studies generally examine individual climate variables such as temperature and precipitation. Thus, we lack a strong understanding of climate change impacts on correlated climate extremes and compound events, which have become more common in recent years. Here we present a monthly‐scale compound warm and dry attribution study, examining CMIP6 climate models with and without the influence of anthropogenic forcing. We show that most regions have experienced large increases in concurrent warm and dry months in historical simulations with human emissions, while no coherent change has occurred in historical natural‐only simulations without human emissions. At the global scale, the likelihood of compound warm‐dry months has increased 2.7 times due to anthropogenic emissions. With this multivariate perspective, we highlight that anthropogenic emissions have not only impacted individual extremes but also compound extremes. Due to amplified risks from multivariate extremes, our results can provide important insights on the risks of associated climate impacts. Plain Language Summary: Most climate change studies tend to explore changes in individual climate variables such as temperature or precipitation. Due to this, we currently do not possess a strong understanding of the multiple changes that can occur simultaneously under human‐driven climate change. Here we present how the simultaneous occurrence of warm and dry months have increased significantly under modeled climate conditions with human emissions, especially relative to modeled climate conditions without human emissions. We highlight that at the global scale, the occurrence of simultaneously warm and dry months has increased 2.7 times under the presence of human emissions. Since the simultaneous occurrence of extreme climate conditions can produce devastating impacts, this study provides an important perspective on the large‐scale multivariate changes that have emerged as a result of human‐driven climate change. Key Points: Using CMIP6 model output, we attribute large increases in concurrent warm and dry months across the globe to anthropogenic activitiesDue to anthropogenic forcing, the global likelihood of warm‐dry months has increased by 2.7 times in land areas between 60°N–60°SWarm‐dry concurrences show largest increases in the tropics and subtropics (Central and South America, Africa, and East and Southeast Asia) [ABSTRACT FROM AUTHOR]

Most attribution studies tend to focus on the impact of anthropogenic forcing on individual variables. However, studies have already established that many climate variables are interrelated, and therefore, multidimensional changes can occur in response to climate change. Here, we propose a multivariate method which uses copula theory to account for underlying climate conditions while attributing the impact of anthropogenic forcing on a given climate variable. This method can be applied to any relevant pair of climate variables; here we apply the methodology to study high temperature exceedances given specified precipitation conditions (e.g., hot droughts). With this method, we introduce a new conditional probability ratio indicator, which communicates the impact of anthropogenic forcing on the likelihood of conditional exceedances. Since changes in temperatures under droughts have already accelerated faster than average climate conditions in many regions, quantifying anthropogenic impacts on conditional climate behavior is important to better understand climate change. Plain Language Summary: Most studies investigating human impacts on climate conditions focus on characterizing changes in individual variables such as precipitation or temperature. However, since many climate conditions are interconnected, these individual variables do not comprehensively represent the many changes that can occur in response to human activity. Here, we introduce a method that takes into account underlying climate conditions while quantifying the impact of human activity on a given climate variable. This method can be used to study pairs of climate variables and here we provide an example application to examine high temperature occurrences during dry precipitation conditions using climate models. For example, we show that regions such as the Amazon have a 4.1 times higher likelihood of experiencing high temperatures under dry climate conditions as a result of human activity. Given our knowledge of future climate change, we anticipate that the relationships between key climate variables may continue to change, which makes the study of human impacts on conditional climate behavior important for a more complete understanding of climate change. Key Points: We propose a multivariate method to conduct an attribution analysis of one variable conditioned on another related climate variableWe show how this method can be applied to high temperature exceedances given specified precipitation conditionsLand regions between 60°N and 60°S show increased risk of conditional temperature extremes under dry conditions due to anthropogenic forcing [ABSTRACT FROM AUTHOR]

Climate extremes threaten human health, economic stability, and the well-being of natural and built environments (e.g., 2003 European heat wave). As the world continues to warm, climate hazards are expected to increase in frequency and intensity. The impacts of extreme events will also be more severe due to the increased exposure (growing population and development) and vulnerability (aging infrastructure) of human settlements. Climate models attribute part of the projected increases in the intensity and frequency of natural disasters to anthropogenic emissions and changes in land use and land cover. Here, we review the impacts, historical and projected changes,and theoretical research gaps of key extreme events (heat waves, droughts, wildfires, precipitation, and flooding). We also highlight the need to improve our understanding of the dependence between individual and interrelated climate extremes because anthropogenic-induced warming increases the risk of not only individual climate extremes but also compound (co-occurring) and cascading hazards. ▪ Climate hazards are expected to increase in frequency and intensity in a warming world. ▪ Anthropogenic-induced warming increases the risk of compound and cascading hazards. ▪ We need to improve our understanding of causes and drivers of compound and cascading hazards. [ABSTRACT FROM AUTHOR]

Climate change is expected to significantly reshape hydropower generation in California. However, the impact on the ability of hydropower to provide reserve capacity that can provide on-demand, back-up electricity generation to stabilize the grid in the case of a contingency has not been explored. This study examined the impact of climate change-driven hydrologic shifts on hydropower contributions to generation and ancillary services. We used projections from four climate models under Representative Concentration Pathways (RCP) RCP4.5 and RCP8.5 to evaluate the impact of climate change conditions, comparing the future period 2046-2055 to the baseline 2000-2009, and observed a net increase of inflow into large hydropower units in northern California. However, as extreme events yield greater spillage, increased overall inflow did not necessarily yield increased generation. Additionally, higher winter generation and summer reservoir constraints resulted in decreases in the spinning reserve potential for both RCP scenarios. We also examined a regionally downscaled "long drought" scenario under RCP8.5 to assess the impact of an extended dry period on generation and spinning reserve bidding. The long drought scenario, developed as part of the California 4th Climate Assessment, involves rainfall congruent with 20-year historical dry spells in California under increased temperatures. In addition to decreased generation, the long drought scenario yielded a 41% reduction in spinning reserve bidding tied to a decline in reservoir levels. The decreased spinning reserve bidding from hydropower may require increased reliance on other electricity resources that can provide the same dynamic support to maintain grid stability under climate change. [ABSTRACT FROM AUTHOR]

In this study, we investigate the extent to which physical water resource availability constraints can limit the deployment of solar thermal and geothermal-based energy resources under future climate scenarios in California. This is accomplished by (1) calculating the water unconstrained potential capacity for solar thermal and geothermal power plants, (2) estimating the available water supply for supporting the water needs of these plants using four climate model simulations under representative concentration pathway (RCP) 8.5, and (3) determining the supportable capacity from the available water supply based on power plant cooling type. We show that regional water availability can limit the installable capacity of solar thermal resources to a range of 10.9–52.6% of solar thermal potential and geothermal resources to between 17.9% and 100% of geothermal potential, depending on cooling system and regional water demand levels by the year 2050. The limiting factor for installable capacity was driven by whether the locations of solar thermal and geothermal resources were spatially aligned with precipitation patterns, with cooling system type acting as a secondary factor. In regions with high solar thermal and geothermal potential, reducing water demand from other sectors was important for alleviating the water constraints on solar thermal and geothermal capacity and increasing total resource potential. Water conservation policies can therefore support the deployment of renewable energy resources and should be considered in future water and energy resource planning. [ABSTRACT FROM AUTHOR]

Highlights • Climate-induced variability in hydropower can increase greenhouse gas emissions. • Higher dispatchable capacity needed to compensate for hydropower variability. • Hydropower under climate change has minimal effects on renewable penetration. • Higher hydropower variability increases natural gas power plant start up events. • Climate-induced hydropower variability increases natural gas power plant downtime. Abstract This study investigates how hydropower generation under climate change affects the ability of the electric grid to integrate high wind and solar capacities. Using California as an example, water reservoir releases are modeled as a function of hydrologic conditions in the context of a highly-renewable electric grid in the year 2050. The system is perturbed using different climate models under the Representative Concentration Pathway 8.5 climate scenario. The findings reveal that climate change impact on hydropower can increase greenhouse gas emissions up to 8.1% due to increased spillage of reservoir inflow reducing hydropower generation, but with minimal effects (<1%) on renewable utilization and levelized cost of electricity. However, increases in dispatchable power plant capacity of +2.1 to +6.3% and decreases in the number of start-up events per power plant unit up to 3.1%, indicate that the majority of dispatchable natural gas power plant capacity is offline for most of the climate change scenarios. While system-wide performance metrics experience small impacts, climate change effects on hydropower generation increase both the need for dispatchable generation and the costs of electricity from these power plants to support large-scale wind and solar integration on the electric grid. [ABSTRACT FROM AUTHOR]