Extreme Heat

As Climate Changes’s previously omnipotent moniker of “global warming” suggests, the world is getting hotter. As greenhouse gases in the atmosphere prevent solar radiation from radiating back into space, the heat energy is reflected back down to Earth, causing global average temperatures to rise. As Figure 1 shows, the past few years have been the hottest years on record, and there is no indication that this trend will reverse1.

Figure 1

Source: National Oceanic and Atmospheric Association, Global Climate Report - November 2020.

Even with the COVID-19 pandemic dramatically reducing international and domestic travel as well as average greenhouse gas emissions, 2020 ranks in the top 3 hottest years on record. The top 6 warmest years have all been since 20152. One of the most widely reported impacts of this ever-increasing amount of heat is the loss of Arctic and Antarctic sea ice, and the effect this has on wildlife like polar bears. However, this increase in temperature also has the ability to deteriorate human health, and exacerbate conditions that lead to illness and injury.

According to the CDC, extreme heat conditions include any weather that is much hotter than average for a particular time and place3. These extreme heat events are becoming more and more common, and are leading to thousands of deaths every year. Vulnerable populations like children, the elderly, minorities, and those suffering from chronic health conditions are particularly at risk for the health impacts of extreme heat, like heat stroke, cardiac arrest, heat cramps and respiratory difficulty4. By 2100, the US EPA projects that United States cities will experience a massive increase in heat-related mortality, as shown by Figure 25.

Figure 2

Source: U.S. EPA. 2015. Climate change in the United States: Benefits of global action. Office of Atmospheric Programs. EPA 430-R-15-0001


Extreme Heat is a global health issue. These maps from the Climate Impact Lab show the average June, July and August temperature predictions for the 21st century if nothing is done to curb greenhouse gas emissions.

Figure 4

But you don’t have to look into the future to see the devastating impacts of extreme heat around the globe. In July 2020, the city of Baghdad, Iraq’s capital city, reached a blistering 125.2°F (51.8°C). This was the hottest recorded temperature the city has ever experienced. As greenhouse gas emissions continue to trap the sun’s energy within our atmosphere, extreme weather conditions like this one will become more and more frequent, likely rendering population centers along the equator uninhabitable.

As urbanization increases across the globe, cities face even more trouble from extreme heat due to the Urban Heat Island Effect. The Urban Heat Island Effect is characterized by urban areas’ tendency to be many degrees warmer than the surrounding suburban and rural areas. This is due to lack of vegetation, which leads to a lack of evapotranspiration (the natural process of trees and other plants naturally cooling the air around them), and the tendency for man-made construction and building materials to absorb and retain the sun’s heat as opposed to reflecting it back into the atmosphere. Additionally, the daily activities of human life in cities generate vast amounts of heat (exhaust from air conditionings cooling buildings, automobile exhaust, etc.). The figure below from the EPA shows how drastic the temperature change can be depending on the type of built environment people live in.

Figure 3

The temperature difference is usually around 1.8-4.5°F warmer than the urban area’s surrounding, but the temperature change can get up to 22°F at night. This is because the man-made construction materials like asphalt and concrete release their heat energy throughout the night, so even when the sun goes down there is little relief from the heat.

To address extreme heat globally, there is little to do to get at the root cause than to stop producing greenhouse gas emissions. To slow the planet-wide warming, the greenhouse gas effect must be slowed down as well. In the meantime, efforts can be made to mitigate the worst of the effects of extreme heat. Increasing the amount of green space in urban areas can help cool down cities thanks to plants’ natural cooling process (evapotranspiration). Similarly, roofs and other surfaces in cities can be painted white, as New York City is doing, to increase reflectivity and decrease heat absorption. Massive investments need to be made to electrify our stoves, change to LED light bulbs, and add heat pumps to increase the efficiency of buildings and to eliminate electricity produced by fossil fuels; these investments will pay out incredible dividends in human health and wellbeing. 


1. NOAA National Centers for Environmental Information. (2020). State of the Climate: Global Climate Report for November 2020. https://www.ncdc.noaa.gov/sotc/global/202011.
2. World Meteorological Organization. (2020). 2020 closes a decade of exceptional heat. https://public.wmo.int/en/media/news/2020-closes-decade-of-exceptional-heat
3. Center for Disease Control and Prevention. (2016). Climate Change and Extreme Heat: What You Can Do To Prepare. cdc.gov/climateandhealth/pubs/extreme-heat-guidebook.pdf
4. Environmental Protection Agency. Heat Islands. (2020). US EPA. https://www.epa.gov/heatislands
5. U.S. EPA. 2015. Climate change in the United States: Benefits of global action. Office of Atmospheric Programs. EPA 430-R-15-0001