Pattern of Mild Weather About to Change

The Environmental Protection Agency says climate change “refers to any significant change in the measures of climate lasting for an extended period of time. In other words, climate change includes major changes in temperature, precipitation, or wind patterns, among other effects, that occur over several decades or longer.”

Scientists have been studying climate change since the 19th century. Over the years scientists have worked to predict how climate change may affect hurricanes, droughts, floods, blizzards and other severe weather, but one area that has been overlooked is mild weather until now. In January, NOAA and Princeton University scientists produced the first global analysis of how climate change may affect the frequency and location of mild weather days. For the purpose of the predictions scientists define mild weather days as temperatures between 64 and 86 degrees F, with less than a half inch of rain and dew points below 68 degrees F, indicative of low humidity.

The research, published in the journal Climatic Change, projects that globally the number of mild days will decrease by 10, or 13 percent, by the end of the century because of climate warming from the buildup of human-caused greenhouse gasses in the atmosphere. Currently the global average is 74 mild days a year. This will drop by four days by 2035 and 10 days by 2081 to 2100. But local variations may be more dramatic. “The hardest-hit areas are expected to be in Africa, Asia and Latin America, where some regions could see 15 to 50 fewer days of
mild weather a year by the end of the century. These are also areas where NOAA and partner research shows economic damages due to climate change. The loss of mild weather days, especially during summer, when they can serve to break up extended heatwaves, also could significantly affect public health,” said the NOAA press release.

Those who live in the mid-latitudes, including most of the United States, as well as many mountainous areas around the world, will gain mild weather days on average. Communities along the border with Canada in the Northeast, Midwest and Northwest, as well as many parts of Canada will be the big winners. Additional areas projected to gain as much as 10 to 15 days more annually of mild weather by the end of the 21st century include parts of England and northern Europe, and Patagonia in extreme southern South America.

New NOAA research using climate models shows a change is coming to the number of mild weather days for major cities in the United States. Chicago will lose 9 days, Miami will lose 28 days, New York City will lose 6 days and Seattle will gain 9 days.

Sarah Kapnick, a physical scientist at NOAA’s GFDL and co-author of the study, said: “We believe improving the public understanding of how climate change will affect something as important as mild weather is an area ripe for more research and more focused studies. Predicting changes in mild weather is not only important to business and industry, but can also contribute to research on the future of physical and mental health, leisure and urban planning.”

Chart courtesy of NOAA

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