A group of researchers, led by Noah Diffenbaugh of Stanford, is developing an outline for a four-step “framework” for testing whether global warming has contributed to record-setting weather events. This framework marks a major shift away from climate scientists’ hesitation to attribute a particular typhoon or tornado to climate change.

This is an example of climate research called “extreme event attribution.” Researchers combine statisticalDrought. Image credit: Creative Commons CC0 analysis of climate data with computer climate models, specifically to evaluate whether individual weather events can be attributed to human-caused global warming.

Diffenbaugh and his group look for “fingerprints” of global warming in extreme weather events. First, they started with the assumption that global warming had no effect on each event they studied. This set a high burden of proof before they could attribute an event to climate change.

The group drew their test cases selected from around the globe—the warmest, wettest and driest events that have occurred in the past decade or so. Among the results is the conclusion that, among the world’s hottest events, global warming attributable to greenhouse gas emissions has increased the odds of extreme events by 80 percent.

For the wettest and driest events, the increase in probability that human-induced climate change contributed to the events is about 50 percent over the cases studied. “Dry” and “wet” events studied include the 2012-2017 California droughts and flooding in India in 2013.

The research team’s multi-pronged approach, setting parameters and testing them against specific weather events, can be used to study not only weather events but also the meteorological events that contribute to the events.

Diffenbaugh sees the demand for rigorous, quantitative event attribution growing in the coming years. “When you look at the historical data, there’s no question that global warming is happening and that extremes are increasing in many areas of the world,” he said. “People make a lot of decisions—short term and long term—that depend on the weather, so it makes sense that they want to know whether global warming is making record-breaking events more likely.”

See this recent Engineering360 article about the effect of low GWP refrigerants on climate change.