Report finds science can estimate climate change’s influence on some extreme events

J. Marshall Shepherd

UGA’s J. Marshall Shepherd contributed to the report, presented March 10 to national leaders

Athens, Ga. – A new report from the National Academies of Sciences, Engineering and Medicine says estimating the influence of climate change on some types of extreme events—such as heat waves, drought and heavy precipitation—is now possible.

The University of Georgia’s J. Marshall Shepherd contributed to the report as a member of the 10-person committee and one of three scientists who briefed government officials in Washington, D.C. Shepherd is the director of UGA’s atmospheric sciences program and the Georgia Athletic Association Distinguished Professor of Geography and Atmospheric Sciences.

The findings, presented to White House and congressional leaders on March 10 by committee members who conducted the study and wrote the report, describes how the relatively new science of extreme event attribution has advanced over the past decade. This is owing to improvements in the understanding of climate and weather mechanisms and the analytical methods used to study specific events.

“An increasingly common question after an extreme weather event is whether climate change ‘caused’ that event to occur,” said committee chair David W. Titley, professor of practice in meteorology and founding director of the Center for Solutions to Weather and Climate Risk at Pennsylvania State University. “While that question remains difficult to answer given all the factors that affect an individual weather event, we can now say more about how climate change has affected the intensity or likelihood of some events.”

Extreme event attribution is a fairly new area of climate science that explores the influence of human-caused climate change on individual or classes of extreme events compared with other factors, such as natural sources of climate and weather variability.

The science typically estimates how the intensity or frequency of an event has been altered by climate change and provides information that can be used to assess and manage risk, guide climate adaptation strategies and determine greenhouse gas emissions targets. For example, in the wake of a devastating event, communities may need to make a decision about whether to rebuild or relocate-and need input on how much more likely or more severe this type of event is expected to become in the future.

“The question of causation between a major hurricane, heat wave or flood and climate change often gets misused by all sides of the discussion,” Shepherd said.

“The study offers better ways to frame these questions and pathways forward to improve our ability to understand linkages between extremes and climate change.”

For example, choices need to be made about defining the duration of the event, the geographic area impacted, what physical variables to study, what metrics to examine and what observations or models to use. These assumptions and choices can lead to large differences in the interpretation of the results and should be clearly stated, according to the report.

The committee supports continued advancements in weather and climate modeling, and notes that focused research on weather and climate extremes would improve event attribution capabilities.

In addition, scientific community standards for attributing classes of extreme events would make it easier to compare results from multiple studies. Objective event selection and definition criteria could help clarify how individual events fit into the broader picture of climate change, they said.

The study was sponsored by the U.S. Department of Energy, Heising Simons Foundation, Litterman Family Foundation, David and Lucile Packard Foundation, National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration and the Arthur L. Day Fund of the National Academy of Sciences.

The National Academies of Sciences, Engineering and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology and medicine. For more information, visit http://national-academies.org.

The report is available online at http://www.nap.edu/catalog/21852/attribution-of-extreme-weather-events-in-the-context-of-climate-change.