The economic impacts of climate change are almost three times higher in large cities like Los Angeles, according to a new study published in Nature Climate Change.

Researchers say the extra costs are due to the urban heat island effect -- a phenomenon in which paved surfaces and buildings absorb and radiate heat causing temperatures in cities to climb as much as 19˚F.

That extra heat has a steep cost: energy use spikes as more people run air conditioners; air pollution worsens as smog forms in hot, stagnant air; people suffer from heat-related illnesses and worker productivity drops.

The study’s lead author, Francisco Estrada, a climate scientist at the National Autonomous University of Mexico, said previous estimates of how much climate change will cost cities overlooked the fact that cities create their own, hotter climates.

A map of Southern California showing temperatures caused by the urban heat island effect. California Environmental Protection Agency

“The effect of the urban heat island is going to amplify the economic impacts of climate change,” he said. “And it’s going to amplify the impacts in a really important, significant manner.”

In Los Angeles, the number of days that downtown temperatures break 95 degrees is expected to triple by 2050. While there isn’t much LA can do on its own to make a big dent in global warming, there are a lot of policies that can mitigate its impact on urban residents.

Mayor Eric Garcetti has pledged to reduce the city’s average ambient temperature three degrees by 2035 through planting trees, installing green roofs and painting pavement light grey to reflect sunlight rather than absorb it. Indeed, the city installed the first "cool street" in the San Fernando Valley earlier this month.

For Estrada, local efforts to fight the urban heat island effect are especially important now.

“You can think about it like insurance,” he said. “If for some reason global agreements fail, as maybe will happen, you are still kind of covered, at least partially.”

President Trump announced in March he would kill the Clean Power Plan, an Obama-era regulation that would have regulated carbon dioxide emissions from the energy sector. The move effectively begins the United States’ retreat from the commitment it made in the 2015 Paris Accord to cut its emissions by up to 28 percent below 2005 levels by 2025.

Even under the worst climate change scenario modeled by the Intergovernmental Panel on Climate Change, in which emissions keep rising and global temperatures jump by 9˚F by 2100, nearly half the economic costs to big cities can be off-set by addressing the urban heat island effect, according to the study. That excludes the costs of sea-level rise.