Under President 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℉ 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℉ by the end of the century. In the most dire scenario (scenario A2), mean global surface temperatures would be nearly 6.5℉ 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.

Under some scenarios, global temperatures could increase by more than 5 degrees by end of century

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.

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U.S. average maximum temperatures have increased by several degrees over the last century

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℉ or higher for the year 2080, the historical number of days per year with a temperature of 90℉ or higher, and the historical average summer maximum and minimum temperatures. The projections assume the IPCC’s high emissions scenario (A2).

To improve relevance, only counties with at least 200,000 people were included in the analysis. Additionally, counties were grouped into the following cohorts based on population size:

  • Small counties: 200,000–349,999
  • Midsize counties: 350,000–749,999
  • Large counties: 750,000 or more

Here are the counties projected to experience the hottest weather.

Small and midsize counties projected to experience the hottest weather

Large Counties Projected to Experience the Hottest Weather

Wind Turbines line the hillsides outside Bakersfield, California
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15. Kern County, CA

  • Projected number of days per year w/ temp above 90°F (for year 2080): 152
  • Historical number of days per year w/ temp above 90°F: 119
  • Historical average summer max temperature: 92.2°F
  • Historical average summer min temperature: 61.4°F

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Downtown skyline. San Antonio, Texas, USA
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14. Bexar County, TX

  • Projected number of days per year w/ temp above 90°F (for year 2080): 158
  • Historical number of days per year w/ temp above 90°F: 112
  • Historical average summer max temperature: 94.9°F
  • Historical average summer min temperature: 71.5°F

Downtown city skyline at twilight. El Paso, Texas, USA
Photo Credit: Alamy Stock Photo

13. El Paso County, TX

  • Projected number of days per year w/ temp above 90°F (for year 2080): 159
  • Historical number of days per year w/ temp above 90°F: 94
  • Historical average summer max temperature: 93.8°F
  • Historical average summer min temperature: 65.8°F

Joshua trees at Joshua Tree National Park
Photo Credit: Alamy Stock Photo

12. Riverside County, CA

  • Projected number of days per year w/ temp above 90°F (for year 2080): 161
  • Historical number of days per year w/ temp above 90°F: 91
  • Historical average summer max temperature: 97.1°F
  • Historical average summer min temperature: 68.6°F

Aerial view of a traffic interchange in Las Vegas
Photo Credit: Alamy Stock Photo

11. Clark County, NV

  • Projected number of days per year w/ temp above 90°F (for year 2080): 168
  • Historical number of days per year w/ temp above 90°F: 117
  • Historical average summer max temperature: 95.9°F
  • Historical average summer min temperature: 69.2°F

Sunset at Clearwater Beach Florida
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10. Pinellas County, FL

  • Projected number of days per year w/ temp above 90°F (for year 2080): 175
  • Historical number of days per year w/ temp above 90°F: 0
  • Historical average summer max temperature: 89°F
  • Historical average summer min temperature: 73.9°F

Downtown skyline. Tampa, Florida, USA
Photo Credit: Alamy Stock Photo

9. Hillsborough County, FL

  • Projected number of days per year w/ temp above 90°F (for year 2080): 185
  • Historical number of days per year w/ temp above 90°F: 51
  • Historical average summer max temperature: 89.7°F
  • Historical average summer min temperature: 71.6°F

Orlando, Florida, USA cityscape
Photo Credit: Alamy Stock Photo

8. Orange County, FL

  • Projected number of days per year w/ temp above 90°F (for year 2080): 188
  • Historical number of days per year w/ temp above 90°F: 57
  • Historical average summer max temperature: 90.8°F
  • Historical average summer min temperature: 71.1°F

Downtown skyline with Sentinel Peak at dusk. Tucson, Arizona, USA
Photo Credit: Alamy Stock Photo

7. Pima County, AZ

  • Projected number of days per year w/ temp above 90°F (for year 2080): 191
  • Historical number of days per year w/ temp above 90°F: 118
  • Historical average summer max temperature: 97.5°F
  • Historical average summer min temperature: 68.6°F

Miami Beach at sunrise
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6. Miami-Dade County, FL

  • Projected number of days per year w/ temp above 90°F (for year 2080): 204
  • Historical number of days per year w/ temp above 90°F: 10
  • Historical average summer max temperature: 89.8°F
  • Historical average summer min temperature: 72.6°F

Downtown cityscape at dusk. Phoenix, Arizona, USA
Photo Credit: Alamy Stock Photo

5. Maricopa County, AZ

  • Projected number of days per year w/ temp above 90°F (for year 2080): 205
  • Historical number of days per year w/ temp above 90°F: 139
  • Historical average summer max temperature: 101.3°F
  • Historical average summer min temperature: 72.5°F

Florida Palm Beach West Singer Island intercostal luxury houses with boats moored at bottom of gardens
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4. Palm Beach County, FL

  • Projected number of days per year w/ temp above 90°F (for year 2080): 209
  • Historical number of days per year w/ temp above 90°F: 11
  • Historical average summer max temperature: 90.2°F
  • Historical average summer min temperature: 71.3°F

High Point Place Fort Myers Florida condominium building
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3. Lee County, FL

  • Projected number of days per year w/ temp above 90°F (for year 2080): 211
  • Historical number of days per year w/ temp above 90°F: 8
  • Historical average summer max temperature: 90.8°F
  • Historical average summer min temperature: 72.3°F

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Beach Broward area with cityscape skyline of residential skyscrapers coastal buildings. Hollywood, Florida in Miami
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2. Broward County, FL

  • Projected number of days per year w/ temp above 90°F (for year 2080): 212
  • Historical number of days per year w/ temp above 90°F: 9
  • Historical average summer max temperature: 90.2°F
  • Historical average summer min temperature: 72.0°F

Palm trees over Mcallen convention center
Photo Credit: Alamy Stock Photo

1. Hidalgo County, TX

  • Projected number of days per year w/ temp above 90°F (for year 2080): 213
  • Historical number of days per year w/ temp above 90°F: 132
  • Historical average summer max temperature: 95.9°F
  • Historical average summer min temperature: 74.3°F

Detailed Findings & Methodology

Perhaps not surprisingly, most of the counties projected to experience the greatest absolute number of extreme heat days (greater than 90°F) in the future are spread out across the southern United States. Interestingly, though, is that 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°F, 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.

Florida is projected to experience the largest increase in 90 degrees F days

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℉ or higher for the year 2080 under a high greenhouse gas emissions scenario (A2) as well as the historical number of days per year with a temperature of 90℉ 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.

To improve relevance, only counties with at least 200,000 people were included in the analysis. Additionally, counties were grouped into the following cohorts based on population size:

  • Small counties: 200,000–349,999
  • Midsize counties: 350,000–749,999
  • Large counties: 750,000 or more