Climate Matters•May 31, 2023
2023 Summer Package
June 1 is the start of meteorological summer. The season is heating up across the U.S.
Since 1970, summers have warmed in 229 U.S. locations—by 2.4°F on average.
Unusually hot summer days now happen more often in 231 locations. And 140 locations now experience at least two more weeks of above-normal summer days than in 1970.
Locations in the West, Southwest, Northwest, and western Texas have seen the most summer heating.
Hotter summers lead to heat-related illness and worsen air quality—putting people at risk.
The 2023 Atlantic hurricane season also begins on June 1. Find reporting resources in our Extreme Weather Toolkit: Tropical Cyclones and recent briefs on hurricane intensity and impacts and flood risk in 23 cities along the Atlantic Coast and Gulf Coast.
The heat is on
Summer temperatures arrived early this year across the northwestern U.S. and western Canada in a record-breaking May heatwave that brought temperatures not typically experienced until July or August.
As carbon pollution traps more heat in Earth’s atmosphere, the summer season is warming, summer temperatures are arriving earlier in the year, and risky heat extremes are becoming more frequent.
Summer warming since 1970
Climate Central analyzed the last 53 years (1970–2022) of summer (June, July, and August) temperature data in 247 U.S. locations. Summaries of the findings below are based on 241 of the locations analyzed (see Methodology):
Summers are getting hotter.
Since 1970, average summer temperatures have increased in 229 (95%) of the locations analyzed.
Summers warmed by 2.4°F on average across these 229 locations.
One-third (75) of these locations warmed by 3°F or more since 1970.
The top five summer warming locations were: Reno, Nev. (11.1°F); Boise, Idaho (5.8°F); Las Vegas, Nev. (5.8°F); Salt Lake City, Utah (5.5°F); and El Paso, Texas (5.3°F).
Summers are heating up everywhere—especially in the western U.S.
Every climate division across the contiguous U.S. has experienced summer heating.
Summers have warmed the most across the West, Southwest, Northwest, and western Texas.
Unusually hot summer days now happen more often.
Since 1970, 231 (96%) of the locations analyzed have seen an increase in the annual number of days above their 1991–2020 summer normal temperature.
More than half of all locations analyzed (140, or 58%) now experience at least two more weeks of above-normal summer days than in 1970.
And 40 locations now experience 30 or more summer days above normal.
The top 10 locations—with between 43 and 66 more with summer days above normal—were in Nevada, Georgia, Texas, Louisiana, and Florida.
Extreme heat is a serious health hazard
More frequent extreme heat is not only an indicator of climate change—it’s also one of the most serious health risks in our warming climate.
Excessive heat is the leading cause of weather-related deaths in the U.S. Climate change is making bouts of deadly heat longer and more frequent.
Exposure to extreme heat makes it difficult for our bodies to cool off, resulting in heat-related illnesses including heat cramps, heat exhaustion, and even fatal medical emergencies such as heat stroke.
Summer heat can also worsen air quality by trapping harmful pollutants close to the Earth’s surface. These pollutants can exacerbate respiratory health issues in people with asthma and other lung diseases.
And as our climate warms, risky heat arrives earlier and lingers later. A recent Climate Central analysis found that 232 U.S. locations have seen the year-round frequency of risky heat days increase—by 21 more days on average since 1970.
Heat risks unequally shared
Extreme heat can affect everyone, but some face greater risks of heat-related illness and mortality than others.
Children, adults over 65, pregnant people, and people living with illness are particularly vulnerable to heat-related illness.
Outdoor workers and athletes are also at elevated risk due to work- and recreation-related exposure to extreme heat.
Structural inequities can also lead to higher extreme heat exposure in some communities. According to a recent study, people of color and people living below the poverty line are disproportionately exposed to urban heat island intensity in 169 of the largest U.S. cities.
POTENTIAL LOCAL STORY ANGLES
Is climate change influencing daily heat extremes in your local area?
Climate Central’s U.S. Climate Shift Index™ Map tool quantifies the influence of climate change on daily high and low temperatures across the entire U.S. The Global Climate Shift Index™ Map tool shows the influence of climate change on daily average temperatures across the entire globe.
How is extreme heat affecting public health in your local area?
The Centers for Disease Control and Prevention Heat and Health Tracker maps heat-related illnesses at the census-tract level in real time. Check the U.S. Department of Health and Human Services monthly Climate and Health Outlook for extreme heat outlooks in your region throughout the summer. Use the National Integrated Heat Health Information System (NIHHIS) Heat Equity Mapper to explore the burden of extreme heat at the census tract level.
What measures are local officials taking to protect people from heat?
The EPA maintains a Community Actions Database of measures that communities are taking to mitigate local heat island effects. Reports from NOAA’s urban heat island mapping campaigns cover local risk reduction and adaptation strategies in 60+ U.S. cities. Track local climate-related hazards in real-time in the Climate Mapping for Resilience and Adaptation Portal, which also includes federal resources for long-term resilience planning. The NIHHIS provides heat preparedness and planning resources. Find your state's emergency management agency to learn more.
Jennifer Vanos, PhD
Associate Professor, School of Sustainability
Arizona State University
Related expertise: extreme heat, urban heat, vulnerable populations
Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts.
Browse maps of climate experts and services at regional NOAA, USDA, and Department of the Interior offices.
Summer (June, July, and August) temperature data from 1970–2022 were obtained from the Applied Climate Information System. Displayed trend lines are based on a mathematical linear regression. Climate Central's local analyses include 247 stations. Data summaries based on linear trends include only 241 stations due to large data gaps in the following six: Dothan, Ala.; Hazard, Ky.; Jefferson City, Mo.; Terre Haute, Ind.; Twin Falls, Idaho; and Wheeling, W.Va.