From Jonathan D. Haskett comes this brief but important CRS report (1 June 2023): Is That Climate Change? The Science of Extreme Event Attribution'.
Download CRS_Report_Is_That_CC_Science_Ext_Event_Attribution_1June2023
I'll just post the summary. Click on the graphics to enlarge them.
Summary
Climate change attribution is the study of whether, or to what degree, human influence may have contributed to extreme climate or weather events. Scientists can now estimate whether human activities have influenced extreme weather or climate events and changed how likely they are to occur. This is known as the science of climate change attribution.Attributions of extreme weather to human-induced climate change may affect how policymakers, organizations, and individuals understand and manage associated risks, with the potential benefit of avoiding future costs. The interpretation and evaluation of attribution findings have been part of the discussion of policy on wildfires, heat waves, climate change, and disaster responses, among other issues. Understanding the attribution process and its uncertainties may be helpful in understanding the potential uses and limitations of climate attribution claims.
Before the development of extreme event attribution methods, there was a scientific consensus that, while attribution of global climate trends was possible, attribution of individual events was not possible. This changed with the development of statistical methods to determine the likelihood that human influence had changed the frequency or severity of extreme events, and a better understanding of the connections between components of the Earth’s climate system.
Several approaches to extreme event attribution have been developed, including a risk-based approach, which seeks to estimate human-influenced changes in the probability of an extreme event, and a storyline approach, which seeks to estimate the relative contribution of specific natural and human causes to an extreme event. The two approaches use many of the same analytic tools. Researchers may study different aspects of the same event, or use differing yet valid analytic methods and find results that seem inconsistent.
Numerous attribution studies have been completed on a wide range of extreme events, including heavy rainfall, heat waves, sea ice extent, consecutive dry days, droughts, and others. Results have included instances where changes in event probability were attributed to human influence, instances where evidence of human influence was not found, and instances where the results were inconclusive. For example, a study of record high May 2017 temperatures in South Korea found that the increased probability of such an event was due to human influence, while a study of a 2011 drought/heat wave in Texas did not find evidence of human influence. In recent years, domestic litigation has been brought by states and municipalities seeking compensation for damage caused by adverse climate impacts. Extreme event attribution may become important in this type of litigation in order to establish liability.
Attribution science is subject to uncertainty. Sources of uncertainty include uncertainty in the observational data, uncertainty in the scientific understanding of natural climate variability, and uncertainty in results produced by climate simulation models. Researchers address these uncertainties using model standardization as well as statistical and analytic methods.
The Chips and Science Act (P.L. 117-167) includes provisions for “the development of software and algorithms to enable the productive application of environmental systems and extreme weather in climate and Earth system prediction models.” In the 118th Congress, the Earth Act to Stop Climate Pollution by 2030 (H.R. 598) includes the finding that “[t]he United States is already seeing climate change exacerbate extreme weather events.” A concurrent resolution (S.Con.Res. 9) includes the finding “that climate change is already increasing the frequency of extreme weather.” Other legislative proposals such as the Green New Deal for Health Act (H.R. 2764) and the Food and Farm Act (H.R. 1824) also include findings stating a causal link between climate change and some extreme weather events.
Climate change attribution has been cited in congressional hearings regarding wildfires, disaster preparedness and the role of the Federal Emergency Management Agency, extreme heat, the impacts of climate change, and the Department of Homeland Security, among other issues. In some cases, experts have disagreed as to the attribution of the same set or type of events. Climate attribution science may help Congress understand related policy issues and evaluate testimony and information presented in hearings and from other sources.
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