Record-breaking high temperatures have made headlines across the globe this summer, drawing attention to one of the most salient and alarming effects of climate change. As global average temperatures rise, extreme high temperatures are expected to increase at an even more rapid rate. The week of July 3^rd 2023 contained two of the hottest days in recorded history, with millions of Americans exposed to dangerously high temperatures representing a dramatic threat to human health and the economy.

The frequency, length, and severity of heat waves have all increased significantly in recent years. Globally, the number of days above 95 degrees Fahrenheit is expected to increase more than threefold by 2100 in the absence of major greenhouse gas emissions reductions. Even under the most optimistic climate projections, the trend of increasing extreme high temperatures is expected to continue, with potentially devastating consequences for human health and wellbeing, particularly among the most vulnerable populations. The scope of this crisis requires both additional actions to address the climate crisis and policies to mitigate the effects of heat.

Heat waves are a growing threat to public health.

Extreme heat directly harms public health, which makes the increasing severity and frequency of extreme heat days all the more concerning. Extreme heat is already the leading cause of weather-related deaths in the United States. Between 2004 and 2018, over 10,000 Americans died of heat-related causes. The true number of heat-related deaths is likely significantly higher, as heat often plays a role in deaths that are officially attributed to other causes.

Health care costs associated with rising temperatures are also considerable and likely to increase over time. A Center for American Progress study based on insurance claims data from 2016 to 2020 estimated that heat-related health care costs in the United States amount to as much as $1 billion each summer.

High temperatures are dangerous to everyone, but infants, children, the elderly, pregnant women, outdoor workers, homeless individuals, and those with preexisting conditions are all especially vulnerable to heat-related illness and death. Prolonged exposure to high temperatures places immense and potentially fatal strain on vital organs and can exacerbate the health impacts of allergens and air pollution. Heat and the resultant dehydration can impair balance and cognition, which may explain why workers tend to have more occupational injuries when temperatures rise.

Elevated nighttime temperatures during a heat wave are especially dangerous because they do not allow for a break from the heat. Even life-saving adaptations to high temperatures can come at a cost, as retreating indoors reduces participation in health-promoting outdoor activities.

Rising temperatures are taking a toll on workers in sectors like food production, transportation, and manufacturing, which will harm the economy now and in the future.

Extreme heat is already having a significant impact on the U.S. economy, particularly in heat-exposed industries like agriculture, mining, construction, manufacturing, and transportation. Crop workers die of heat-related illnesses at 20 times the rate of other civilian workers in the United States. Between 1992 and 2016, 285 construction workers died from heat exposure—accounting for more than 30% of heat-related occupational deaths during that period.

Heat is also significantly impacting the working conditions of mail and shipping delivery workers. Demands for heat mitigation technologies (air conditioning, fans, heat shields) were front and center in the recent contentious contract negotiations between UPS and its 340,000 Teamsters union members.

Together, the loss of productivity caused by heat is emerging as one of the biggest economic costs of climate change. A recent study on the effect of temperature on productivity found that, while extreme heat harms agriculture, the impact on productivity in manufacturing and other sectors is larger – in part because they are more labor-intensive. Heat increases absenteeism and reduces work hours and these effects are expected to grow as the world warms. In 2021, data showed that more than 2.5 billion hours of labor in the U.S. agriculture, construction, manufacturing, and service sectors were lost to heat exposure. Another report found that, in 2020, loss of productivity from heat exposure cost the economy $100 billion with annual costs expected to grow to $500 billion by 2050. A recent study showed that as temperatures reach 90 degrees Fahrenheit productivity drops by about 25%, and it falls by 70% as temperatures reach 100 degrees Fahrenheit.

Heat waves and higher average temperatures are also increasingly damaging to crops and livestock, with potentially devastating consequences on our food system. Since 2001, heat-related crop losses have led to over $1.3 billion in federally-subsidized crop insurance payouts to farmers in six states in the Southwest—New Mexico, Arizona, California, Nevada, Colorado, and Utah. Heat waves have resulted in lost livestock, more expensive cooking oil, and shortages of staple grains like wheat. In the long term, increases in average temperatures may benefit some farmers by extending growing seasons and opening new growing regions; however, in the short term, they can result in significant losses and price volatility as producers struggle to drastically adapt their operations.

The future economic costs associated with extreme heat depend largely on the extent and pace of emissions reductions. Global average temperatures are currently on track to rise by 2.7 degrees by 2100. Even if more than 70% of nations were to meet their proposed net zero targets, warming is still expected to reach at least 1.8 degrees—well above the 1.5 degree target established by the Paris Agreement. The United States is projected to lose an average of 14 labor hours per weather-exposed worker per year if the global temperature rise is contained to 2 degrees Celsius. If there is an increase of 4 degrees, lost productivity is expected to more than double. In areas of the Southeast, Southern Great Plains, and Southwest, the direct effects on productivity are likely to be substantially above the national average.

The relative importance of vulnerable sectors to local and state economies can amplify the direct economic impacts of heat. As the table below shows, workers in the most heat-exposed industries comprise a significant share of the workforce across the country. In Wisconsin and Indiana, nearly 1/3 of workers are employed in heat-exposed industries. Relatively small changes to working hours due to heat will have outsized economic impacts in states where more people work in heat-exposed industries. The following table includes the total number of employees in heat-exposed industries in each state and their share of each state’s total workforce.