Sunrise from Otay Mountain
Sunrise viewed from Otay Mountain on a hot day. Photo courtesy UCSD HPWREN network

Absent significant global action to address climate change, San Diego County will see dramatic spikes in annual extreme-heat days by the end of the century, according to a report released Tuesday by a scientific advocacy group.

The report by the Union of Concerned Scientists, a nonprofit group that has long pushed for worldwide efforts to combat climate change, offers detailed predictions of anticipated temperature increases in areas across the United States under various scenarios, including varying degrees of political action by international leaders.

The report states that San Diego County averages 42 days per year with a heat index of 90 degrees or more, meaning days on which the temperature “feels like” 90 degrees or higher. With no action taken to address climate change, that number will jump to 77 days a year by mid-century, and 109 days a year by 2099.

If worldwide leaders take some moderate action on climate change, those numbers can be cut to 69 days a year by mid-century and 80 days a year by century’s end, the report estimates. If bold action is taken — on the level outlined in the Paris climate agreement — the number of 90-degree heat-index days can be limited to 71 a year in San Diego County by 2099, according to the report.

UCS officials said the 90-degree heat index represents the point at which outdoor workers “generally become susceptible to heat-related illness.”

According to the report, Los Angeles County historically has averaged two days a year with a heat index of 105 degrees or more, but that will increase to 13 per year by mid-century and 26 per year by century’s end if no climate-change action is taken.

“Extreme heat is among the deadliest weather hazards society faces,” according to the report, titled “Killer Heat in the United States: Climate Choices and the Future of Dangerously Hot Days.”

“During extremely hot days, heat-related deaths spike and hospital admissions for heat-related deaths rise, especially among people experiencing poverty, elderly adults and other vulnerable groups,” the report states. “Temperatures around the world have been increasing for decades in response to rising heat-trapping emissions from human activities, primarily the burning of fossil fuels. These rising temperatures are causing more days of dangerous — even deadly — heat locally.”

The report makes no secret of the UCS’ advocacy for action on climate change, insisting its findings lay out a clear need for a global response.

“If we wish to spare people in the United States and around the world the mortal dangers of extreme and relentless heat, there is little time to do so and little room for half measures,” according to the report. “We need to employ our most ambitious actions to prevent the rise of extreme heat — to save lives and safeguard the quality of life for today’s children, who will live our their days in the future we’re currently creating.”

Statewide, California averages 40 days a year with a heat index of 90 degrees or more. According to the report, that number would jump to 68 days a year by mid-century without any action on climate change, and to 92 days a year by the end of the century.

— City News Service

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Chris Jennewein

Chris Jennewein is Editor & Publisher of Times of San Diego.