Climate Matters•July 30, 2024
Rising Heat Risks for Workers
KEY CONCEPTS
Heat exposure on the job presents health and safety hazards, causes heat-related illness, injury, or death, and impacts livelihoods through lost labor hours and wages.
Humid heat is especially dangerous for weather-exposed workers, and has been rising as our climate warms.
Nearly all (89%) of 242 U.S. locations analyzed by Climate Central have seen an increase in the number of annual warning days for workers (heat index of 80°F to 94°F) since 1979.
Locations across the Ohio Valley and Upper Midwest have experienced the largest increases.
Workers in locations across the Southeast, South, and Southwest experience an average of 103-130 warning days each year.
At least half of the days each year are a warning day for workers in: Miami, Fla. (199 days), West Palm Beach, Fla. (190 days), and Ft. Myers, Fla. (184 days).
Lost labor hours due to heat are projected to increase as the climate continues to warm, affecting livelihoods and economies in the U.S. and around the globe.
Heat-related injury, illness, and deaths on the job are preventable, but heat-specific protections for workers are not yet widespread and there are no comprehensive nationwide standards.
Download local data
Extreme heat and weather-exposed workers
Climate change is causing hotter, longer, and more frequent extreme heat events — the leading cause of weather-related deaths in the U.S. Heat can be dangerous for anyone, but some face higher risks.
This includes weather-exposed workers who regularly work in hot temperatures, high humidity, intense radiation from the sun, or with limited air circulation or cooling.
About one-third of all U.S. workers were regularly exposed to the outdoors as a part of their job last year — especially those in agriculture, construction, landscaping, and public safety.
People working indoors without air conditioning or near radiant heat sources such as in kitchens, factories, or foundries also face higher risks for heat-related illness, injury, and death.
Our warming climate amplifies risks to weather-exposed workers’ health, safety, and livelihoods.
Heat on the job: dangerous and costly
In the most extreme cases, heat exposure on the job can lead to death. From 1992 to 2022, 986 U.S. workers died from exposure to heat. About one-third of these deaths occurred among construction workers. The average rate of heat-related workplace deaths over this period (34 per year) accounts for about 19% of all heat-related deaths in the U.S. (183 per year, 1994-2023).
Heat on the job presents a range of other health and safety hazards such as a higher likelihood of workplace accidents. The U.S. Bureau of Labor Statistics estimates that from 2011 to 2020 there were 33,890 work-related heat injuries and illnesses resulting in days away from work.
Statistics on occupational heat-related illness, injury, and death are likely underestimated due to underreporting, inconsistent reporting, and the difficulty of attributing symptoms or death to heat.
Heat also poses indirect dangers to weather-exposed workers beyond direct physiological impacts. For example, workplace harassment and discrimination may be more likely in hotter temperatures.
Extreme heat can also be costly due to lost work hours and wages or healthcare expenses from heat-related workplace injuries. From 1980 to 2016, an average of 421 million U.S. work hours were lost annually due to heat. The average annual cost of these losses was $14 billion (in 2016 dollars).
On a global scale, heat led to the loss of 490 billion potential work hours in 2022 alone.
Humidity multiplies workplace heat risks
When heat is combined with high humidity, the health risks multiply. As humidity rises, sweat evaporates more slowly and removes less heat from our bodies. High levels of humid heat can overwhelm the body’s temperature control system and lead to serious and even fatal heat stress and illness.
There are several different ways to measure humid heat. Common metrics like the heat index and wet bulb globe temperature are both based on relative humidity and are more useful than air temperature alone in determining risks for weather-exposed workers.
Learn more about humid heat metrics: Humid Heat: Hidden but Hazardous
OSHA recommends using wet bulb globe temperature, which incorporates temperature, relative humidity, wind speed, and solar radiation, to monitor heat hazards in the workplace.
Extreme wet bulb globe temperatures have doubled in frequency from 1980-1999 to 2000-2019 across most major US regions.
Although wet bulb globe temperature is a more accurate metric for hazard assessment by occupational health professionals, the heat index also provides a useful hazard screening metric that is more widely available in local forecasts.
Within the OSHA-NIOSH Heat Safety Tool, heat index-based risk screening levels for workers are established as:
Caution days for workers: heat index less than 80°F
Warning days for workers: heat index of 80°F to 94°F, inclusive
Danger days for workers: heat index of 95°F or higher
According to OSHA, serious occupational heat-related illnesses and injuries become more frequent on days with a heat index above 80°F — especially among unacclimatized or physically active workers.
More warning days for midwestern workers
To understand how risky days for workers are changing in our warming climate, Climate Central analyzed temperature and relative humidity data from 242 U.S. locations to assess the changing frequency of warning days for workers (a heat index of 80°F to 94°F, inclusive) from 1979 to 2023.
Nearly all (89% or 215) of the 242 locations have experienced an increase in the number of annual warning days for workers since 1979.
These 215 locations now experience an average of 11 more warning days annually than in 1979.
The rise in warning days was concentrated in the northern and midwestern regions — and highest in the Ohio Valley, which now experiences 13 more warning days annually than in 1979.
Workers in locations analyzed across the Upper Midwest, Northeast, and Northern Rockies and Plains now experience an average of 12 more warning days annually relative to 1979.
More danger days for southern workers
Climate Central also analyzed temperature and relative humidity data from 236 U.S. locations to assess the changing frequency of danger days for workers (a heat index of 95°F or higher).
About 60% (141) of the 236 locations have experienced an increase in the number of annual danger days for workers since 1979.
Although fewer locations have seen an increase in danger days compared to warning days, top-ranked locations skewed toward even larger increases: up to 43 more danger days annually in Miami.
The rise in danger days was concentrated in the South and Southeast. Workers in locations analyzed across these regions now experience an average of 14 and 11 more danger days annually, respectively, than in 1979.
City | Change in warning days for workers (Heat Index 80°F to 94°F), 1979-2023 | City | Change in danger days for workers (Heat Index 95°F+), 1979-2023 |
|---|---|---|---|
Erie, Pa. | 28 | Miami, Fla. | 43 |
Colorado Springs, Co. | 27 | West Palm Beach, Fla. | 41 |
Bluefield, W.Va. | 23 | McAllen, Texas | 38 |
Lincoln Area, Neb. | 21 | San Angelo, Texas | 34 |
Higher heat risk for workers in the Southeast, South, and Southwest
To see where in the U.S. workers typically face the highest levels of heat risk, Climate Central also assessed the average annual number of warning and danger days in each location over the last 30 years (1994-2023).
Average annual warning days for workers:
Locations across the Southeast, South, and Southwest faced the most warning days annually during the past 30 years.
Workers in these regions experience an average of 130 (Southeast), 112 (South), and 103 (Southwest) warning days each year.
At least half of the days each year are a warning day for workers in: Miami, Fla. (199 days), West Palm Beach, Fla. (190 days), and Ft. Myers, Fla. (184 days).
Average annual danger days for workers:
Locations across the Southeast, South, and Southwest also faced the most danger days annually during the past 30 years.
Workers in these regions experience an average of 66 (South), 51 (Southeast), and 37 (Southwest) danger days each year.
At least one out of every three days each year are a danger day for workers in: McAllen, Texas (135 days), Laredo, Texas (129 days), and Palm Springs, Calif. (121 days).
Working in a warming climate
If intermediate to high levels of emissions of heat-trapping pollution continue (RCP 4.5 and 8.5, respectively), weather-exposed workers in the U.S. could experience annual lost wages ranging from $37 to $80 billion (in 2015 dollars) by 2090 due to decreased time spent working on days over 90°F.
With 2°C of global warming, climate-driven increases in high-temperature days are projected to result in 14 lost labor hours per year. In that warming scenario, the largest labor losses due to extreme heat are likely to occur in the Southern Great Plains and the Southeast, where the average weather-exposed worker is projected to lose 26 and 20 hours per year.
Levels of future labor loss due to extreme heat depends on what we do now. If global warming is kept below 1.5°C with rapid global climate action, it could prevent about 77 million hours of heat-related labor loss by 2050, compared to a business-as-usual scenario.
If climate action is delayed and global temperatures continue to rise, workers will have fewer options to adapt to risky heat. Effective adaptation measures such as shifting work hours from midday to cooler early mornings become more limited as warming continues.
Preventing risk and protecting workers
Heat-related injury, illness, and deaths on the job are preventable. Supervisors and workers can reduce risk by:
Building heat tolerance through gradual acclimatization, especially during the first weeks on the job.
Workplace training on heat hazards, recognizing symptoms of heat-related illness, first aid, and procedures for contacting emergency medical services.
Ongoing monitoring and response to heat hazards including: wet bulb globe temperature, heat sources (e.g., furnaces) in work areas, physical work demands, reduced heat shedding due to clothing or protective gear, and individual health risk factors.
Requiring levels and frequency of hydration, rest, shade, and cooling that are appropriate for current and forecasted heat hazards and for individual worker risk factors (including clothing, health, acclimatization, and proximity to heat sources).
Despite these proven effective measures, heat-specific protections for workers are not yet widespread and there are no comprehensive federal standards. Only five states (California, Colorado, Minnesota, Oregon, and Washington) have workplace standards for heat exposure. And in fact two states (Florida and Texas) have legislation that prevents local municipalities from establishing their own laws relating to heat and worker safety.
A proposed federal rule announced in July 2024 by the Biden-Harris Administration could help protect approximately 36 million weather-exposed workers, especially in high-risk industries such as construction, agriculture, and manufacturing.
In the absence of comprehensive federal or state legislation, some cities are taking steps to protect weather-exposed workers. For example, in June 2024, Tucson, Arizona adopted an ordinance that requires employers under city contracts to use heat safety standards to prevent heat-related illness and injuries for their workers.
LOCAL STORY ANGLES
Monitor risk levels for workers in your local area
The OSHA-NIOSH Heat Safety Tool App is a resource for finding the forecasted and current heat index near your location, and the level of worker risk those conditions present. The Heat Safety Tool App is a screening tool; it does not replace a more accurate wet bulb globe temperature-based hazard assessment which is the core tool used by occupational health professionals.
How are heat and humidity changing in your area?
The National Weather Service forecasts wet bulb globe temperature across the country. For long-term projections, check out this interactive heat index map from the Union of Concerned Scientists.
CONTACT EXPERTS
Luke Parsons, Ph.D. (he/him)
Applied Climate Scientist, Global Science
The Nature Conservancy
Relevant expertise: impacts of humid heat on health and labor productivity
Contact: luke.parsons@tnc.org
*Limited availability August 3 to August 11, 2024
Matthew Neidell, Ph.D.
Professor, Health Policy and Management
Columbia University
Relevant expertise: environmental, health, and labor economics
Contact: mn2191@cumc.columbia.edu
FIND EXPERTS
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.
Explore databases such as 500 Women Scientists, BIPOC Climate and Energy Justice PhDs, and Diverse Sources to find and amplify diverse expert voices.
Reach out to your State Climate Office or the nearest Land-Grant University to connect with scientists, educators, and extension staff in your local area.
METHODOLOGY
Daily maximum temperature and minimum relative humidity data (1979-2023) for the contiguous United States were obtained from the gridMET dataset. Heat index temperatures were calculated using the National Weather Service’s heat index algorithms. The annual number of days with a heat index at warning (heat index of 80°F to 94°F, inclusive) and danger (heat index of 95°F or higher) levels for workers (based on risk screening thresholds in the OSHA-NIOSH Heat Safety Tool App) were assessed for 242 locations from 1979 to 2023. The local change in annual days above a heat index of 80°F (shown in local graphics) is based on linear regression. Of the 242 locations analyzed, six were excluded from the analysis of danger days as they do not see heat index values at or above 95°F: Butte, Mont.; Cheyenne, Wyo.; Colorado Springs, Co.; Eureka, Calif.; Flagstaff, Ariz.; and Monterey, Calif.
The state-level reported worker heat deaths from 2017 to 2022 were obtained from OSHA. The county-level lost labor hour data comes from Neidell et al., 2021.