August 2, 2018

With Rising Global Warming Emissions, Most of US Could See 20 to 30 More Days of Extreme Heat Annually by Mid-Century

Crippling and sometimes deadly heat waves have blanketed many countries across the world thus far this season, including the United States. The Union of Concerned Scientists (UCS) has released two new synthesis fact sheets on extreme heat. The first examines changes in the frequency, intensity and duration of extreme heat events like heat waves, as well as the role of climate change in driving current and future trends. The second reviews the impacts and implications of extreme heat—including on health and infrastructure reliability—within the United States. These fully referenced fact sheets summarize the latest science, making them ideal for citing in stories on extreme heat events when a scientific source is needed.

According to the fact sheets:

  • Over the last five decades, many parts of the United States have seen an increase in the frequency of intense heat waves.
  • Every region of the country is projected to experience hotter temperatures in the 21st century.

➢    In the next few decades, if carbon emissions continue to grow, most of the country could see 20 to 30 more days annually with maximum temperatures above 90 degrees Fahrenheit. The Southeast could be hit even harder, potentially enduring 40 to 50 more such days.

➢    By the end of the century, the entire United States is likely to experience more frequent and intense heat waves than what is experienced today, with the Southeast, Southwest and Alaska expected to see the biggest increases.

  • Some U.S. residents are at greater risk of adverse health effects and death in the face of these changes in extreme heat. Low-income residents, the young and elderly, construction and agricultural workers, individuals with pre-existing medical conditions, and people living in the center of urban areas can be more vulnerable to physical harm from heat.

“Climate change is making heat waves both more likely to happen and hotter than in the past, such that they’re becoming increasingly disruptive and dangerous to our daily lives,” said Rachel Licker, senior climate scientist in the Climate and Energy Program at UCS. “Extreme heat means more emergency calls and heat-related illnesses, especially for people who are very young, elderly, work outdoors, or don’t have regular access to air conditioning. Extreme heat can also lead to cancelled school days where buildings lack cooling, as well as increased energy use to meet the greater cooling demand.”

Scientists are increasingly able to attribute individual extreme weather events such as heat waves to the influence of human-caused climate change. Click here to check out a UCS fact sheet released in June that examines the science connecting extreme weather events to climate change.

Heat waves are costly, damaging and dangerous. In 2012, for example, much of the contiguous United States experienced a catastrophic, prolonged heat wave and associated drought that directly caused more than 120 deaths and resulted in $33 billion in losses. Despite the evident human and economic toll of extreme heat, the nation has not yet implemented the policies, nor allocated the resources, needed to adequately rein in global warming emissions, bolster our public health responses and assist communities heavily impacted during heat waves.

“Our nation’s annual temperature highs are likely to increase by at least 10 degrees Fahrenheit by 2100 compared to what we experienced at the end of the 20th century if we continue releasing global warming emissions under business-as-usual conditions,” said Juan Declet-Barreto, climate scientist at UCS. “But if nations were to meet the goals of the global Paris climate agreement, the increase in temperature highs could be limited to less than four degrees Fahrenheit—still a public health and safety challenge, no doubt, but markedly more manageable for people and communities.”

The Union of Concerned Scientists puts rigorous, independent science to work to solve our planet's most pressing problems. Joining with people across the country, we combine technical analysis and effective advocacy to create innovative, practical solutions for a healthy, safe, and sustainable future.