Hot, hotter, hottest: How much will climate change warm your county?

Within two decades, climate change will have a striking but uneven effect on temperatures across the United States, according to a USA TODAY analysis of climate projection data.

The Gulf Coast could experience a significant increase in extreme heat. Large parts of the northern U.S. could see dramatic warming. And across the country, more Americans may be exposed to the harmful effects of heating.

These findings are part of a USA TODAY analysis of data from the Climate Impact Lab . The analysis uses county-level temperature projections to assess how annual warming and extreme heat are expected to change from 2020 to 2040.

Like most climate projections, this data shows the nation warming over the next two decades. But the analysis also highlights the potential for cooler regions of the U.S. to experience a significant increase in average annual temperatures. Meanwhile, hotter regions are expected to see the biggest increase in days above 90 degrees.

“We’re already experiencing an increase in warming and extreme heat across the country,” says Kelly McCusker, a climate scientist at the Climate Impact Lab. “I think a lot about how that will worsen ... and how that heat affects people unequally.”

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Here’s what to know about the projections:

USA TODAY used data from climate models that make two main assumptions. First, future population and economic development follow historical patterns. Second, stringent climate policies enable significant emissions reductions by 2100.

Scientists refer to this set of assumptions as a “middle of the road” scenario for how social and economic changes may affect how climate change unfolds.

Technically, the scenario is named SSP2-4.5 , and it is just one of many possible climate scenarios.

USA TODAY grouped counties with similar increases in warming into three categories.

• Roughly 1,100 counties are projected to see a “significant” increase of 2.6 to 4.5 degrees in average annual temperatures.
• More than 1,600 counties with an increase of 2.1 to 2.6 degrees may see “moderate” warming.
• Just 517 counties are likely to experience “minimal” warming: an increase of 1.0 to 2.1 degrees in annual temperatures.

These boundaries were chosen because they represent natural “breaks” in the distribution of data.

Significantly warmer temperatures for cooler regions

Counties in the U.S. that are known for their cooler climates could expect a large increase in temperatures by 2040.

• Northern Alaska may experience more warming than any other part of the country.
• Parts of the Great Plains and Midwest are projected to warm by more than 3 degrees.
• Most counties are projected to warm by 2.1 degrees to 2.5 degrees.
• Counties along the East and West coasts may experience the least warming.

The northernmost county of Alaska is expected to warm faster than any other, with annual average temperatures projected to increase by 4.5 degrees by 2040. Research suggests regions around the Arctic are experiencing up to three times more warming than other parts of the planet because of a phenomenon known as polar amplification. Parts of Alaska are within the Arctic Circle, and the state has already warmed more than the lower 48 states since 1970.

Continued warming in these areas could affect the distribution and availability of fish and wildlife that rural Alaskans depend on for survival. Warming in other parts of the United States may have similar consequences on food supplies.

Warming waters: Alaska's snow crabs suddenly vanished. Will history repeat itself as waters warm?

One-fourth of the United States’ farmlands are in the Great Plains, where a 3-degree temperature rise could have huge effects on agriculture. Greater warming in this region could extend the frost-free season but also increase heat-related crop failures. Weather-related crop insurance payouts from the federal government have already risen significantly since 2001, with heat as a cause of loss increasing over 1,000% according to an analysis of Department of Agriculture data by the Environmental Working Group.

“Economic dependence on crops, rangelands, and recreation makes residents with land-based livelihoods vulnerable to climate-related changes in weather,” according to the Fifth National Climate Assessment . Warming in this region could have uncertain consequences for local farmers.

There’s also bad news for areas that aren’t expected to warm very much.

Coastal counties are generally projected to experience less warming than inland regions, but experts warn these places may not be safe from the effects of climate change.

“It’s really a sleight of hand that makes them appear like they’re in better shape,” says climate researcher Brian Brettschneider. “Really they’re not in better shape.”

Though such counties can remain cooler because the ocean absorbs and distributes a significant amount of heat, the regions remain vulnerable to more frequent flooding from rising sea levels and extreme rainfall , as well as damage from powerful tropical storms.

Dangerous heat on the rise in warmer regions

Many counties that already experience warm weather will face many more days of dangerous heat within two decades, according to the projections.

USA TODAY grouped together counties based on the number of additional days above 90 degrees they may experience.

• More than 1,000 counties are projected to see the “most” increase: more than 21 additional days above 90 degrees.
• Nearly 750 counties with 14 to 21 additional days above 90 degrees may experience “more” increase in extreme heat, while nearly 640 counties with seven to 14 additional days are expected to see “some.”
• Roughly 830 counties are projected to see “few” additional days of extreme heat: fewer than seven more days above 90 degrees.

These categories also closely approximate natural “breaks” in the distribution of data.

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Those groupings show regions that could face a notable increase in extreme heat risk:

• Counties in the Florida Peninsula are projected to experience the greatest increase in days above 90 degrees.
• The Southeast and parts of the Midwest may see over three additional weeks of extreme heat, although those days will likely be spread out throughout the year.

Exposure to extreme heat can be uncomfortable at best, making it difficult to focus when learning or working. At worst, it can be deadly. Heat is already the leading cause of climate-related deaths in the U.S., and more days above 90 degrees may increase the number of heat-related deaths and illness.

Extreme heat kills and maims. Here are some of its victims from across the US.

When the air temperature exceeds 90 degrees, the human body begins to gain more heat than it can release. Sweating can allow the body to cool further, but in especially hot and humid climates, sweat may not evaporate fast enough, which can cause the body’s internal temperature to rise dangerously.

Children and older adults are most at risk of developing heat-related health complications, especially when they have preexisting conditions.

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Although people accustomed to warmer climates can be overwhelmed by extreme heat, it poses the biggest threat in places not prepared for hot weather.

“You can imagine a local elementary school may not have air conditioning yet, and that has real consequences when it’s a 90-degree day in a city that’s not used to that,” McCusker says.

Adding more green spaces to urban areas, installing more air conditioning and constructing cooling centers can help people avoid the worst effects of heat, but not all communities have the funding to implement these solutions.

Across the country, escaping the effects of climate change may become more challenging. While historically cooler regions are getting a lot hotter, hotter regions are facing more dangerous heat.

People may be able to adjust to a rapidly warming country, but "we have the ability now to reduce the worst impacts simply by reducing emissions now,” McCusker says. “And we’ve shown that lives can be saved.”

Abhinav Krishnan is a climate data intern for USA TODAY. Reach him on X at @AbhinavSKrish .

This article originally appeared on USA TODAY: Hot, hotter, hottest: How much will climate change warm your county?