Publication Date April 29, 2017 | Arizona Daily Star

Greenhouse gases likely aggravated Tucson's record March heat, researcher says

United States
Image: National Weather Service Tucson
Image: National Weather Service Tucson

Human-caused climate change was at least partly to blame and probably mostly to blame for Tucson’s record-setting March heat, says a researcher with expertise in this field.

At the Star’s request, researcher Geert Jan van Oldenborgh of the Netherlands analyzed possible factors for explaining Tucson’s March temperatures, which averaged nearly 8 degrees above normal overall when daytime highs and nighttime lows are accounted for.

He concluded that long-term temperature trends point almost certainly to human-caused greenhouse-gas emissions as a factor. The unresolved question, he said, is how big of a factor they are.

That longer-term increase was more than 7 degrees Fahrenheit in average high temperatures since about 1950, said van Oldenborgh. He’s a senior researcher for the Royal Netherlands Meteorological Institute, the country’s equivalent of the U.S.’s National Weather Service.

That is a much faster increase than has occurred globally, he said.

Van Oldenborgh’s analysis illustrates a new trend in climate-change research: showing that human-produced greenhouse-gas emissions cause extreme weather events. For a long time, many climate scientists said it’s not possible to attribute such events to long-term climate change. But a U.S. National Academy of Sciences study released last summer concluded that such attribution is possible if done in a scientifically valid manner.

Van Oldenborgh’s analysis wasn’t a formal, peer-reviewed study. But, “I can tell you unequivocally that he used methodologies that the National Academy of Sciences committee agreed were appropriate,” said Kathy Jacobs, a University of Arizona specialist in climate change adaptation who, like van Oldenborgh, sat on the academy committee that produced the 2016 report.

She said evidence of global warming is “incredibly clear across Southern Arizona, and it is undoubtedly a contributing factor in the heat wave in March.”

Jacobs, who led the publication of the federal government’s 2014 National Climate Assessment, now directs the UA’s Center for Climate Adaptation and Solutions.