Abstract: Effective climate risk management requires robust quantification of the probability of different kinds of hazards, such as heat waves, droughts, floods, and severe storms. As a result, there has been increasing interest in the extent to which historical global warming has influenced the occurrence and severity of individual extreme climate events. However, although trends in the extremes of the seasonal- and daily-scale distributions of climate records have been analyzed for many years, quantifying the contribution of observed global warming to individual events that are unprecedented in the observed record presents a particular scientific challenge. I will describe a framework for leveraging observations and large climate model ensembles to quantify the influence of observed global warming on the probability of unprecedented extreme events. This approach is grounded on three tenets: (1) Focus on understanding the physical causes of the individual event; (2) Use formal uncertainty quantification to test the probability of those physical conditions occurring in the current climate; and (3) Use formal hypothesis testing to compare the probability of those physical conditions occurring in the current climate and a climate without human influence. My group has applied our analysis to a number of different climate variables from a number of individual events, including temperature, precipitation, soil moisture, and atmospheric circulation patterns. Together, this work has shown that global warming can influence the risk of extreme events that are unprecedented in historical experience, particularly by altering the probability of the physical conditions that are responsible for the event. In addition, given the widespread public interest in “real time” attribution, the prospects for operational attribution analysis will also be discussed.
About the Speaker: Noah Diffenbaugh is a Professor and Kimmelman Family Senior Fellow at Stanford University. He studies the climate system, including impacts on agriculture, water resources, and human health. He is currently Editor-in-Chief of Geophysical Research Letters. He has served as an IPCC Lead Author, and has provided scientific expertise to the White House, the Governor of California, and U.S. Congressional offices. Recognitions include the Holton Award from the American Geophysical Union and a CAREER award from the National Science Foundation.