A modest sign of warming
Is the Texas drought and heat wave due to climate change or natural variation? “There is no doubt a modest component related to climate change, while natural variability plays a major role,” says Kevin Trenberth, a climatologist at the National Center for Atmospheric Research. “Fifteen years ago we suggested that with ENSO [El Nino-Southern Oscillation; periodic variations in water temperatures in the Pacific] the floods and droughts would become more intense.”
The strong La Nina of the past year has been strongly associated with the Southwest drought and heavy rainfall in the Mississippi Valley, Trenberth says. In many respects, “It is almost classic … except in California.
Although the drought is linked to La Nina, it is also exacerbated by climate warming, Trenberth adds. Human climate change adds “about a 1 percent to 2 percent effect every day in terms of more energy. So after a month or two this mounts up and helps dry things out. At that point all the heat goes into raising temperatures. So it mounts up to a point that once again records get broken. The extent of the extremes would not have occurred without human climate change.”