Global warming has increased risk of record heat

Yottafire: Drought shriveled crops in the Midwest, massive wildfires raged in the West and East Coast cities sweltered. The summer of 2012 was a season of epic proportions, especially July, the hottest month in the history of U.S. weather record keeping. And it’s likely that we’ll continue to see such calamitous weather.

In the north-central and northeastern United States, extreme weather is more than four times as likely to occur than it was in the pre-industrial era, according to a new study by Noah Diffenbaugh, a Stanford associate professor of environmental Earth system science, and Martin Scherer, a research assistant in the department.

Diffenbaugh and Scherer found strong evidence that the high levels of greenhouse gases now in the atmosphere have increased the likelihood of severe heat such as occurred in the United States in 2012. The researchers focused primarily on understanding the physical processes that created the hazardous weather. They looked at how rare those conditions were over the history of available weather records, going back over the last century.

Then, using climate models, they quantified how the risk of such damaging weather has changed in the current climate of high greenhouse gas concentrations, as opposed to an era of significantly lower concentrations and no global warming. Their findings don’t pinpoint global warming as the cause of particular extreme weather events, but they do reveal the increasing risk of such events as the world warms.

“Going forward, if we want to understand and manage climate risks, it’s more practically relevant to understand the likelihood of the hazard than to ask whether any particular disaster was caused by global warming,” Diffenbaugh said....

A 2000 fire in the Bitterroot National Forest in Montana, USDA photo