skip to main content

→ Top Stories:
Clean Power plan
Safe Chemicals

Juan Declet-Barreto’s Blog

Climate Change Impacts from the National Climate Assessment: Focus on Effects of Extreme Heat on Human Health

Juan Declet-Barreto

Posted June 13, 2014

, , , ,
Share | | |

Summer is around the corner, and with it comes some welcome warm weather and some not-so-welcome heat waves. After living in Arizona for almost 20 years and now living in Washington, DC, I know what it’s like to go through a long string of uncomfortably hot days. In fact, I recall when multiple-day spells of temperatures 100 ºF or higher in Phoenix were a relatively rare occurrence. Unfortunately, because of climate change, heat waves have worsened not just in Phoenix, but in every region in the country—and the longer and stronger the heat wave, the more our health suffers.

In this first of a series of blogs on health and climate change, I will describe the consequences of existing and future extreme heat to human health due to increasing global temperatures. The Third National Climate Assessment, released on May 6, 2014, provides a comprehensive overview of current and projected heat health consequences of climate change in the United States.

What are the current climate change-related health impacts of extreme heat?

There is plenty of scientific evidence that shows that climate change has increased the frequency and severity of summertime heat waves—especially in the western United States—and that these extremes are posing grave threats to public health. Average temperatures in the U.S. have increased by 1.3 to 1.9 ºF since 1895, and most of the increase has happened in the last 40 years. Although all regions in the U.S. have experienced warming recently, the pace of change has been faster in the northern U.S., while the southeast U.S. has seen the smallest changes in temperature since 1970.

Heat waves have long threatened human health in cities like St. Louis, Philadelphia, Chicago, and Cincinnati, and these cities have recently seen large increases in heat-related deaths attributable to heat waves. During heat waves, deaths and illness can occur from conditions caused by direct heat exposure (like heat stroke), but extreme heat can also trigger hospital admissions or death from existing conditions like cardiovascular, respiratory, or cerebrovascular diseases.

Thumbnail image for Number of days with temperatures over 100 ºF during 2011

Increased warming due to global climate change (from carbon pollution generated by power plants, for example) is affecting the health of populations across the world, but local warming in cities due to the Urban Heat Island is also putting people at risk. Some of the populations most vulnerable to heat in cities include the elderly, who have diminished capacity for regulating their bodily temperature and often live on fixed incomes. Low-income minorities, who often have little economic resources to pay for preventive health care, air conditioning, and typically work in outdoor environment jobs like landscaping or construction, are at higher risks to extreme heat death or illness than the general population.

Although some of the health risks associated with extreme heat have decreased in the U.S. due to increased access to air conditioning, improved forecasting, and heat-health warning systems, fatalities due to extreme heat are still a cause of preventable death. In fact, the Centers for Disease Control (CDC) has found that heat is the number one weather-related killer in the U.S, and unless we put the brakes on temperature rises, it is likely to continue to do so. As we will see below, adverse health impacts from climate changed-induced heat waves are projected to increase.

What’s expected in the future?

Assuming that rapid emissions reductions can be achieved by year 2100, models predict average temperature increases of 3-5 ºF across the U.S, but under a scenario of continued increases in emissions, the projected changes in temperature jump to a whopping 10-15 ºF hotter. These predictions suggest much hotter cities and locales throughout the country, which will drive up deaths and illnesses due to extreme heat.  On top of that, hotter temperatures will lead to more ozone in the lower atmosphere because air pollutants called ozone precursors  “cook” in the air immediately above cities to form the health-threatening gas, which will further worsen the health of those with existing respiratory conditions like asthma and emphysema.

Projected increases in urbanization will also drive up the vulnerability of populations: as cities and metropolitan areas increase in size, so do their Urban Heat Islands. Increased warming in cities due to the heat island will continue to disproportionately impact the poor and ethnic minorities in cities, further increasing their heat-related health burden. 

Projected temperatures under emissions reductions and increases scenarios

But it’s not all doom and gloom; there’s hope for a healthier environmental future! The U.S. Environmental Protection Agency (EPA) just released a proposal for the first-ever standards on carbon pollution, a measure that will reduce global warming-causing pollution from power plants by an average of 30 percent across the United States.  A recent Harvard School of Public Health report estimates that carbon pollution standards will have a beneficial impact on air quality by reducing harmful pollutants, which will mean increased human health benefits.  Carbon pollution standards and other measures to curb climate change will help reduce human deaths and illnesses from extreme heat. As more details on the clean power rules become available and considered in health assessments like the Harvard study, the already strong support across the U.S. for reducing carbon emissions and for creating a more healthy environment will undoubtedly increase. 

Watch this space for more human health impacts of climate change!

Share | | |


Switchboard is the staff blog of the Natural Resources Defense Council, the nation’s most effective environmental group. For more about our work, including in-depth policy documents, action alerts and ways you can contribute, visit

Feeds: Juan Declet-Barreto’s blog

Feeds: Stay Plugged In