Most climate change detection and attribution studies have focused on mean or extreme temperature or precipitation, neglecting to explore long-term changes in drought characteristics. Here we provide ...evidence that anthropogenic forcing has impacted interrelated meteorological drought characteristics. Using SPI and SPEI indices generated from an ensemble of 9 CMIP6 models (using 3 realizations per model), we show that the presence of anthropogenic forcing has increased the drought frequency, maximum drought duration, and maximum drought intensity experienced in large parts of the Americas, Africa, and Asia. Using individual greenhouse gas and anthropogenic aerosol forcings, we also highlight that regional balances between the two major forcings have contributed to the drying patterns detected in our results. Overall, we provide a comprehensive characterization of the influence of anthropogenic forcing on drought characteristics, providing important perspectives on the role of forcings in driving changes in drought events.
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.
While the relationships between dry land surface conditions, heat, and aridity have been well‐established, few studies have addressed whether global warming will affect the ability of wet conditions ...to moderate high temperatures and atmospheric aridity. Using Coupled Model Intercomparison Project Phase 6 models, we demonstrate that absolute changes in the monthly maximum temperature distribution during Central North American summers strongly outweigh the historical cooling effect of high precipitation and soil moisture conditions. Although wet conditions nearly always prevent concurrent extreme temperatures in the baseline period, these conditions are 40%–48% and 96%–98% less effective at 1 and 2° of global warming, respectively. However, high precipitation and soil moisture partially retain the ability to constrain concurrent high vapor pressure deficit conditions below historical thresholds at 1–2° of warming. Our results highlight the growing vulnerability of Central North America to warmer temperatures and drier atmospheric conditions, even during periods of high precipitation and soil moisture.
Plain Language Summary
In this study, we examine whether warming global temperatures will affect the ability of wet conditions, which we define with precipitation or soil moisture, to prevent the occurrence of concurrent high temperatures and dry atmospheric conditions. Focusing on the Central Plains region in North America, we show that even at 1° of global warming, high precipitation, and high soil moisture conditions already partially lose the ability to prevent high maximum temperatures in the summer months. In contrast, we show that high precipitation and high soil moisture conditions are able to better retain the ability to prevent dry atmospheric conditions even at 2° of global warming. Our results indicate that the Central Plains region will quickly become more exposed to warmer and drier climate conditions, even during periods with high precipitation and soil moisture, with potentially serious implications across public health, economic, and environmental sectors.
Key Points
Absolute changes in the temperature distribution due to global warming outweigh cooling effects from wet conditions in the Central Plains
Meanwhile, wet conditions can still partially constrain extreme atmospheric aridity below historical levels under global warming
Differences in heat and aridity responses are mainly dependent on underlying changes in the temperature and aridity distributions
Abstract
Daytime heat is often associated with reduced soil moisture and cloud cover, while nighttime heat is connected to high humidity and increased cloud cover. Due to these differing mechanisms, ...compound daytime and nighttime heat events may respond differently to major anthropogenic forcings (greenhouse gases, anthropogenic aerosols, land-use and land-cover change). Here, we use GISS ModelE2.1-G historical single-forcing runs from 1955 to 2014 to examine how individual anthropogenic forcings affect compound heat events—specifically warm daytime and nighttime temperatures compounded with dry precipitation or high humidity conditions. We show that greenhouse gases alone amplify the natural frequency of warm-dry events by 1.5–5 times and warm-humid events by 2–9 times in tropical and extratropical latitudes. Conversely, aerosols and land-use/land-cover change reduce the frequency of these events, resulting in more modest increases and in some regions, declines, in the historical ‘all-forcings’ scenario. Individually, aerosol effects are stronger and more widespread compared to land-use, oftentimes reducing the natural frequency of these events by 60%–100%. The responses of these compound events are primarily driven by changes in daytime and nighttime temperatures through large-scale warming via greenhouse gases and cooling from aerosols and land-use/land-cover change. However, changes in warm-dry events are amplified in regions with concurrent precipitation declines (e.g. Central America, Mediterranean regions) and warm-humid events are amplified by global concurrent humidity increases. Additionally, we find differences between daytime and nighttime compound responses in the historical experiment that can be traced back to the individual forcings. In particular, aerosols produce a greater cooling effect on daytime relative to nighttime temperatures, which notably results in a historical reduction of Northern Hemisphere daytime warm-dry events relative to natural conditions. Our analysis provides a more comprehensive understanding of the significant impacts of different anthropogenic climate forcings on daytime and nighttime warm-dry and warm-humid events, informing future risk and impact assessments.
Atmospheric warming is projected to intensify heat wave events, as quantified by multiple descriptors, including intensity, duration, and frequency. While most studies investigate one feature at a ...time, heat wave characteristics are often interdependent and ignoring the relationships between them can lead to substantial biases in frequency (hazard) analyses. We propose a multivariate approach to construct heat wave intensity, duration, frequency (HIDF) curves, which enables the concurrent analysis of all heat wave properties. Here we show how HIDF curves can be used in various locations to quantitatively describe the likelihood of heat waves with different intensities and durations. We then employ HIDF curves to attribute changes in heat waves to anthropogenic warming by comparing GCM simulations with and without anthropogenic emissions. For example, in Los Angeles, CA, HIDF analysis shows that we can attribute the 21% increase in the likelihood of a four-day heat wave (temperature > 31 °C) to anthropogenic emissions.
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 variable
We show how this method can be applied to high temperature exceedances given specified precipitation conditions
Land regions between 60°N and 60°S show increased risk of conditional temperature extremes under dry conditions due to anthropogenic forcing
•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.
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.
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 activities
Due to anthropogenic forcing, the global likelihood of warm‐dry months has increased by 2.7 times in land areas between 60°N–60°S
Warm‐dry concurrences show largest increases in the tropics and subtropics (Central and South America, Africa, and East and Southeast Asia)
During droughts, low surface moisture may translate surface heating into warming, since excess energy will be converted into sensible heat instead of evaporating as latent heat. Recent concurrent ...occurrences of droughts and heatwaves have caused compounding ecosystem and societal stresses, which prompted our investigation of whether there has been a shift in temperatures under meteorological drought conditions in the United States. Using historical observations, we detect that droughts have been warming faster than the average climate in the southern and northeastern United States. Climate model projections also show a pronounced warming shift in southern states between the late 20th and 21st centuries. We argue that concurrent changes in vapor pressure deficit and relative humidity influence the amplified warming, modifying interactions between the land surface and the atmosphere. We anticipate that the magnified shift in temperatures will bring more concurrent extremes in the future, exacerbating individual impacts from high temperatures and droughts.
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