D.C. Averages A Week Of 100-Degree Days. Climate Change Could Make That Two Months.

Historically, D.C. experienced a week’s worth of days where it felt like 100 degrees. By 2050, there could be almost six weeks (41 days) where the heat index rises to 100 degrees. By the end of the century, D.C. could be sweating through a solid two months and one week of days that feel like 100 degrees. This is all if the world takes no serious action to reduce greenhouse gas emissions.

“Some people may say, ‘Oh, this is the worst-case scenario,’ ” says Astrid Caldas, a climate scientist at the Union of Concerned Scientists. “It’s not the worst-case scenario, it’s the scenario we’re on right now.”

Caldas is one of the authors of a new analysis of the effect climate change will have on extreme heat across the United States. The Union of Concerned Scientists used 18 climate models to project the change in extreme heat, depending on how quickly the world takes action to reduce carbon emissions.

The report includes projections for three different emissions scenarios — rapid action, slow action and no action. If the world does take quick action, drastically cutting emissions, that would limit the number of 100 degree heat index days in D.C. to an average of 30 per year — less than half as many as the no action scenario.

Heat index is a calculation of how hot it really feels, taking into account temperature and relative humidity. Heat index is used by the national Weather Service as the basis for heat advisories and warnings.

There has already been lots of research on how climate change will impact extreme temperatures, but the authors say this is the first analysis to take a high-resolution look at how hot it will really feel in the U.S., using the heat index.

The study looks at four different categories of extreme heat: days above 90 degrees heat index, days above 100, days above 105, and — frighteningly — days that are “off the charts.” These off the charts days — above 130 degrees — were extremely rare back in the 1970s when the heat index was developed, occurring in the United States only in Sonoran Desert in Arizona and California.

By the end of the century, there could be an entire week of these miserable days in D.C. each year, if no action to reduce emissions is taken. 07-16-19

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