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Extreme heat, deluges and economic pain: What the UN climate report says for North America

USA TODAY logo USA TODAY 10/10/2018 Josh Hafner
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A United Nations report this week outlined the water scarcity, flooding and extreme heat risks possible within decades due to global warming.

Though the U.N. Intergovernmental Panel on Climate Change focused on "rapid, far-reaching" actions needed to avert calamity the world over, it spelled out specific dangers for North America.

Heavy rainfall, extreme heat and economic fallout could worsen in North America if the atmosphere rises another degree Celsius above preindustrial levels, the report said.

The Earth is already 1 degree Celsius (1.8 degrees Fahrenheit) above, and whether it jumps to 1.5 or 2 degrees C (2.7 to 3.6 F) in coming years could make a big difference.

Here's what North America could face, per the report:

Extreme heat gets worse

A region's climate can change drastically between 1.5 and 2 degrees Celsius, particularly in temperature extremes. The highest levels of warming for extremely hot days would occur in the eastern and central USA – from the Dakotas south to Texas and toward the East – as well as parts of Asia, Africa, Europe and the Mediterranean. 

That's because soil in those regions tends to dry out. The Earth's surface uses available water to cool off, just like humans do with sweat, said Natalie Mahowald, a Cornell University climate scientist who helped author the report.

"If there is no water to evaporate, then there is more increase in temperature, since the surface can’t cool by evaporating water," she said.

Heavy rain more likely

Topping 2 degrees Celsius (3.6 degrees Fahrenheit) would risk increasing heavy rainfall in North America from Ohio to Georgia and toward the East, one of several regions where the largest increases in extreme rain and snow would occur. 

"This region tends to see more extreme precipitation for a variety of reasons," Mahowald said. "But to say it simply: It’s because warmer air holds more water, so in a warmer world, there is more water to precipitate out."

Other regions primed for deluges include Alaska, Canada and parts of Europe and Asia.

All that heavy rain could link to increasingly intense hurricanes – though they may not become more frequent.

Higher economic tolls

"The economic damages of climate change in the USA are projected to be large," the report's authors concluded. They cited two studies that predict a higher economic toll if warming reaches 2 degrees by the year 2100 instead of halting at 1.5 degrees.

One of the studies, led by Solomon Hsiang, a public policy professor at the University of California-Berkeley, found America's economic damage equates to about 1.2 percent of the nation's gross domestic product for every 1 degree increase in warming.

New Orleans under water

Melting ice and warmer oceans already pushed sea levels nearly a foot or more around the USA, and moving past 1.5 degrees to 2 degrees could increase sea level rise globally by roughly a half-meter or more by 2100.

Resource Watch, an environmental data group, estimated that's enough to put America's East and Gulf Coasts at risk, leaving parts of New Orleans under water.

Follow Josh Hafner on Twitter: @joshhafner

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