More Extremely Hot Days

KEY CONCEPTS

• The summer season is expanding—creeping into spring, lingering into fall, and shrinking winter. 

• With a longer summer-feeling season, we experience more extremely hot days year-round across the country.

• Since 1970, 74% (184) of 246 U.S. locations analyzed reported more extremely hot days annually. 

• About 51% (126) of the locations had at least seven additional extremely hot days annually.

• Extreme heat can take a toll on the body and increase the risk of heat-related illnesses and hospitalizations.

As our planet undergoes a climate change-induced fever, we are experiencing hotter temperatures than normal. The summer season is expanding, creeping into spring, lingering into fall, and subsequently, shrinking winter. With a longer summer-feeling season, we experience more hot days year round across the country.

Extremely hot days are on the rise–but the temperature threshold for extreme heat is different across the U.S. A high of 80°F is considered sweltering hot in Fairbanks, AK, but a normal average in Miami. And 100°F is common in Phoenix, but treated as a dangerous heat advisory in New York City. Different locations have different temperature thresholds for defining an “extremely hot day” depending on their climatology. However, with climate change, the U.S. is experiencing more hot days across the board.

A look at the numbers: Climate Central analysis looked at 246 U.S. locations and calculated how many more days each year were extremely hot from 1970 to 2021. 

• Since 1970, 74% (184) of 246 U.S. locations analyzed reported more extremely hot days annually. 

• About 51% (126) of the locations had at least seven additional extremely hot days annually.

• The largest change was in Austin, TX with 43 additional days above 100°F.

What’s the role of climate change in extremely hot days? Climate Central’s new tool, the Climate Shift Index (CSI), allows us for the first time to quantify how human-caused climate change has changed the odds of daily temperatures across the country. Access the tool to find CSI values for your local high and low temperatures for yesterday, today, and the next two days. 

Extreme heat can take a toll on the body. People in historically cooler regions may be less acclimatized to heat, and lack the infrastructure (like central air conditioning) to cope with it. A 2019 study found that heat-related hospitalizations begin at lower heat values in traditionally cooler regions (such as the Northwest, West, and Northeast) compared to the South and Southeast. An example is the June 2021 Pacific Northwest heatwave where temperatures reached triple digits and resulted in many hospitalizations and hundreds of deaths. 

Heat also impacts us unequally. According to the Centers for Disease Control and Prevention, the most vulnerable populations to excessive heat are children, athletes, adults over 65, outdoor workers, low income households, and people with chronic medical conditions.

POTENTIAL LOCAL STORY ANGLES

How is heat affecting health?

Check out the resources in the Heat section of our Climate Change and Health toolkit. In addition, the 2018 National Climate Assessment details how the rise of extreme heat is already impacting health. The CDC also distills these health risks into infographics (both English and Spanish). 

LOCAL EXPERTS 

The SciLine service, 500 Women Scientists or the press offices of local universities may be able to connect you with local scientists who have expertise on extreme heat and climate change. The American Association of State Climatologists is a professional scientific organization composed of all state climatologists. 

NATIONAL EXPERTS 

Ahira Sánchez-Lugo
Physical Scientist
NOAA National Centers for Environmental Information (NCEI), Center for Weather and Climate (CWC)
Contact: Ahira.Sanchez-Lugo@noaa.gov
*Available for interviews in Spanish and English

Cheryl L. Holder, MD
Associate Dean for Diversity, Equity, Inclusivity, and Community Initiatives and Associate Professor at Florida International University
Topics: climate change, health and equity
Contact: (954) 483-7685 

METHODOLOGY

The temperature threshold used for each city was determined based on the 95th percentile of the average maximum summer temperature rounded up to the nearest 5 degrees. The count of days includes all months and was retrieved from the RCC-ACIS database. Climate Central's local analyses include 247 stations. However, for data summaries based on linear trends, only 246 stations are included due to large data gaps in Wheeling, W. Va.