15 Counties Projected to Experience the Hottest Weather

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Editor's Note: This story originally appeared on Porch.

Under President Joe Biden, the U.S. has pledged to cut greenhouse gas emissions by at least 50% by 2030. This pledge will require aggressive action and is almost double the target that the U.S. made under the 2015 Paris Climate Agreement. However, without significant action by the U.S. and other major polluting countries, scientists predict that global temperatures will continue to rise. In the absence of a significant curb in greenhouse gas emissions, data from the U.S. Geological Survey (USGS) shows that some parts of the U.S. will spend over 60% of the year with temperatures above 90 degrees Fahrenheit by the year 2080.

The Intergovernmental Panel on Climate Change (IPCC) — the United Nations body that evaluates the science related to climate change — predicts that under certain scenarios global temperatures could increase by upwards of 5 or 6 degrees by the end of the century. In the most dire scenario, mean global surface temperatures would be nearly 6.5 degrees higher relative to historical average temperatures from the years 1980 to 1999. However, global warming and temperature increases are not uniform, and some places will experience temperature increases that are much greater than average.

In addition to a rise in mean global temperatures, climate change will continue to bring more unusually hot summer days. In the U.S., mean maximum temperatures have increased by several degrees since the late 1800s. More common extreme summer heat waves will make living in some parts of the country more uncomfortable and dangerous. Heat can worsen droughts, and hot, dry conditions will increase wildfire risk. Human health will also be impacted as heat-related illnesses become more prevalent.

Some parts of the U.S. already have a high number of extremely hot days every year, but even places with a more mild climate could see a significant increase in extreme temperature events. To find the counties projected to experience the hottest weather, researchers at Porch analyzed data from the USGS and NOAA. Researchers calculated the projected number of days per year with a temperature of 90 degrees F or higher for the year 2080, the historical number of days per year with a temperature of 90 degrees F or higher, and the historical average summer maximum and minimum temperatures. The projections assume the IPCC’s high emissions scenario.

Here are the large counties (population 750,000 or more) projected to experience the most days of 90 degrees or higher temperatures in 2080.

15. Kern County, CA

Cantil in Kern County California
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 152
  • Historical average summer maximum temperature: 92.2°F
  • Historical average summer minimum temperature: 61.4°F

14. Bexar County, TX

San Antonio at night.
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 158
  • Historical average summer maximum temperature: 94.9°F
  • Historical average summer minimum temperature: 71.5°F

13. El Paso County, TX

El Paso Texas neighborhood
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 159
  • Historical average summer maximum temperature: 93.8°F
  • Historical average summer minimum temperature: 65.8°F

12. Riverside County, CA

Joshua Tree National Park in California
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 161
  • Historical average summer maximum temperature: 97.1°F
  • Historical average summer minimum temperature: 68.6°F

11. Clark County, NV

Las Vegas homes
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 168
  • Historical average summer maximum temperature: 95.9°F
  • Historical average summer minimum temperature: 69.2°F

10. Pinellas County, FL

St. Petersburg, Florida
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 175
  • Historical average summer maximum temperature: 89°F
  • Historical average summer minimum temperature: 73.9°F

9. Hillsborough County, FL

Tampa, Florida
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 185
  • Historical average summer maximum temperature: 89.7°F
  • Historical average summer minimum temperature: 71.6°F

8. Orange County, FL

Orlando, Florida
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 188
  • Historical average summer maximum temperature: 90.8°F
  • Historical average summer minimum temperature: 71.1°F

7. Pima County, AZ

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  • Projected number of days per year w/ temp above 90°F (for year 2080): 191
  • Historical average summer maximum temperature: 97.5°F
  • Historical average summer minimum temperature: 68.6°F

6. Miami-Dade County, FL

Miami Beach Ocean Drive at dusk
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 204
  • Historical average summer maximum temperature: 89.8°F
  • Historical average summer minimum temperature: 72.6°F

5. Maricopa County, AZ

Phoenix, Arizona
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 205
  • Historical average summer maximum temperature: 101.3°F
  • Historical average summer minimum temperature: 72.5°F

4. Palm Beach County, FL

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  • Projected number of days per year w/ temp above 90°F (for year 2080): 209
  • Historical average summer maxmum temperature: 90.2°F
  • Historical average summer minimum temperature: 71.3°F

3. Lee County, FL

Fort Myers, Florida
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 211
  • Historical average summer maximum temperature: 90.8°F
  • Historical average summer minimum temperature: 72.3°F

2. Broward County, FL

Fort Lauderdale Florida
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 212
  • Historical average summer maximum temperature: 90.2°F
  • Historical average summer minimum temperature: 72.0°F

1. Hidalgo County, TX

Rio Grande River in McAllen Texas
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  • Projected number of days per year w/ temp above 90°F (for year 2080): 213
  • Historical average summer maximum temperature: 95.9°F
  • Historical average summer minimum temperature: 74.3°F

Detailed Findings & Methodology

Man in front of fan on computer
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Perhaps not surprisingly, most of the counties projected to experience the greatest absolute number of extreme heat days (greater than 90 degrees F) in the future are spread out across the Southern U.S. Interestingly, though, counties in Florida are projected to experience the largest increase in the number of extreme heat days when comparing future projections to the historical record. Historically, many coastal communities in Florida reported very few, if any, days that exceeded 90 degrees, but models predict these areas could experience more than 150 days of extreme heat annually as the end of the century approaches. Increases in temperature combined with Florida’s sea-level rise risks make it one of the most vulnerable states to climate change.

To find the counties projected to experience the hottest weather, researchers at Porch analyzed the latest data from NOAA’s Climate Normals Dataset and the USGS’s 1/8th-degree-CONUS Daily Downscaled Climate Projections, accessed from the CDC’s National Environmental Public Health Tracking Network. The USGS data contains the projected number of days per year with a temperature of 90 degrees or higher for the year 2080 under a high greenhouse gas emissions scenario as well as the historical number of days per year with a temperature of 90 degrees or higher (using the average over the years 1980 to 2010). NOAA’s Climate Normals data provides the historical average summer maximum and minimum temperatures, averaged over the years 1901–2000.

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