Climate Change to Bring More Hot Days to Los Angeles Region: UCLA Study

The first-ever regional study showed a significant increase in the number of extremely hot days

The Los Angeles region is expected to see more days above 95 degrees by the middle of the 21st Century, according to a first-ever report from UCLA on the local impacts of climate change.

The report, "Mid-Century Warming in the Los Angeles Region," predicts that temperatures will rise an average of 4.6 degrees Fahreneit if greenhouse-gas emissions continue to increase at current levels.

The change would mean three times today's number of extremely hot days in downtown LA, and four times as many in the surrounding valleys and mountain areas. 

At a press conference Thursday morning in Echo Park to announce the findings, UCLA climate researcher Alex Hall said, "One of the study's unexpected findings is that the mountains themselves show more warming than elsewhere."

There may be fluctuations in patterns of highs and lows between 2041 to 2060 – the 20-year period examined in the report – but overall, the region will be warmer, researchers said.

"The changes our region will face are significant, and we will have to adapt," said Hall, the study's author, in a university news release. "Every season of the year in every part of the county will be warmer."

The report from Hall, an associate professor in UCLA's Department of Atmospheric and Oceanic Sciences, is part of a project called Climate Change in the Los Angeles Region that is intended to help planners and policymakers account for future conditions in a region with some $750 billion in annual economic activity.

Hall said the report doesn't dictate actions that local governments might take with the new information.

" We provide the numbers, but it's up to the people of the LA region to decide what to do," Hall said.

Los Angeles Mayor Antonio Villaraigosa said the report need to be taken seriously, and that the city needed to take action in response.

"This stuff isn't a luxury. We've got to do it," Villaraigosa said.

"Southern Californians should expect slightly warmer winters and springs but much warmer summers and falls, with more frequent heat waves," according to the report's website.

The report "downscaled" 22 global climate models and integrated the results to observe climate change's influence at the neighborhood level -- within a grid of 1.2-mile squares.The data includes Los Angeles and Orange counties and parts of Ventura, San Bernardino and Riverside counties.

The study predicts that temperatures now seen on the seven hottest days of the year will by mid-century occur two to six times as often, depending on the area. 

Coastal areas such as Santa Monica and Long Beach are likely to see less of a temperature rise: 3 to 4 degrees, as shown in the UCLA chart below. Densely developed areas such as downtown Los Angeles and the surrounding valleys will see an uptick average of 4 degrees, while mountain areas and deserts will warm 4 to 5 degrees.

Overall, areas separated from the ocean by at least one mountain range are expected to warm 20 to 50 percent more than coastal areas of the LA basin, especially in summer.

"Places like Lancaster and Palm Springs are already pretty hot areas, and when you tack on warming of 5 to 6 degrees, that's a pretty noticeable difference," Hall said in the UCLA release. "If humans are noticing it, so are plants, animals and ecosystems. These places will be qualitatively different than they are now."

Even if greenhouse-gas emissions are significantly reduced, the study found that temperatures in the region will still increase to about 70 percent of the levels predicted in business-as-usual scenario described above.

"Even if we drastically cut pollution worldwide, there will still be quite a bit of warming in Los Angeles. I was a little taken aback by how much warming remains, no matter how aggressively we cut back. It was sobering," Hall said in the UCLA release.

The report is the first of five expected releases from Climate Change in the Los Angeles Region.

The report was produced – with federal funding provided to the city of Los Angeles – in partnership with the Los Angeles Regional Collaborative for Climate Action and Sustainability, a network of government, business, academia and non-profit groups.

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