Heat sickness | Science News for Students

Heat sickness

Higher temperatures and dirtier air appear to be leading to more hospital visits — and early deaths
May 31, 2016 — 7:15 am EST

Climate change and pollution will combine to send more people to hospital emergency rooms in coming years, new research concludes.

zilli / iStockphoto

In recent decades, Earth’s climate has been changing. That’s led to warmer temperatures and more very hot days. At the same time, levels of air pollution are growing. All that heat and dirty air will cause a lot more people to sicken — and even die. That’s the conclusion that emerges from three new analyses of climate trends in the eastern United States.

“We all know that climate change is warming up the world in general,” says Gregory Wellenius. He studies air pollution, public health and climate change at Brown University in Providence, R.I. Wellenius is also the lead author of one of the new studies. It was published in the April Environmental Health Perspectives.

Earlier research had strongly linked high temperatures to kidney disease, cardiovascular diseases (heart attacks, strokes and high blood pressure) and respiratory diseases (asthma, chronic lung disease and pneumonia), notes Wellenius. “People who are dehydrated or feel unwell due to heat,” also sometimes go to the hospital, he adds.

overheated runner“The United States and New England seem particularly vulnerable,” he adds. “So you might ask, how many extra deaths or emergency department visits will we see by the end of the century due to climate change?"

To find out, he and his colleagues began by asking two questions. Is there a link between emergency room (ER) visits and heat-related deaths now? And how much are temperatures likely to climb between now and the end of the century?

Using those global-warming estimates, the researchers projected health trends by the end of the century. Their calculations now suggest there could be “1,000 to 3,000 extra deaths at the end of the century,” he says. And that’s just in Rhode Island, the seventh smallest U.S. state in terms of population. Those “extra deaths” are people who would die earlier than they otherwise should have.

How they got those numbers

To make those calculations, the researchers first turned to hospital records. They focused on ER visits for heat-related health problems in Rhode Island between 2005 and 2012. Then they looked at temperature records. They compared the pattern of those ER visits to that of daily temperature highs.

What they found was disturbing. As daily high temperatures rose from 24º to 29º Celsius (75º to 84º Fahrenheit), the projected number of heat-related ER visits climbed between 1.3 percent and nearly 24 percent. At the same time, deaths from all causes rose 4 percent. Put simply: Heat-related illnesses and deaths went up as the number of days with temperatures above 24 ºC (75 ºF) increased.

ER doctor“This is important,” says Wellenius. With global warming, temperatures across the planet are expected to grow in coming years.

His research also suggests these premature deaths would occur between April and October, typically the hottest time of year.

But, Wellenius adds, “It’s also important to note that these numbers aren’t precise. And we don’t know exactly how the climate will change or what climate change will do to health.” Yet based on what is known about climate change, he points out that “extremely hot days [will] happen a lot more often.”

Also unknown is whether people will be able to adapt, over time, to the higher temperatures. Their bodies may do this biologically. But communities might also increase their use of heat-reducing technologies, such as air conditioning.

Some communities in high-income countries already have programs to help prevent heat-related health emergencies. Some cities, for instance, open air-conditioned cooling centers on very hot days. “More widespread adoption of these and similar programs in the future could mitigate [prevent] future heat-related mortality,” says Michael Brauer. He studies global health impacts of air pollution at the University of British Columbia’s School of Population and Public Health in Vancouver, Canada.

Air pollution ups the health impacts

In a second study, researchers in Maryland linked extreme heat to increases in asthma — a condition that causes trouble breathing. An estimated 439,000 people are already hospitalized each year in the United States for asthma. Bad cases can even lead to death.

Sutyajeet Soneja works at the University of Maryland School of Public Health in College Park. He was part of a team from this school and the state health department in Baltimore. Together, they analyzed medical records from 2000 to 2012. Extreme heat spiked hospitalizations for asthma in Maryland throughout the year by at least 3 percent. But summers were worst. In those months, hospital visits for asthma linked to extreme heat rose by almost eight times that rate.

girl inhalerThe exaggerated effect in summer may be due to the heat cooking up air pollutants from fossil fuels, creating ozone-rich smog. This smog can irritate the lungs.

Soneja’s team reported its findings April 27 in Environmental Health.

Extremely hot days also will increase the harm caused by another type of air pollution. It’s known as particulate matter. In general, the smaller these dust-like bits are, the deeper they can enter into the lungs. Some also can be inhaled up the nose and into the brain, where they can cause damage.

Joel Schwartz studies the health effects of pollution at Harvard’s T.H. Chan School of Public Health in Boston, Mass. He and his colleagues analyzed health data from New Jersey. And they uncovered a cause-and-effect link between increased particulates in air and death rates.

“When the concentrations of fine [very small] particulates in the air went up, deaths went up,” Schwartz reports. His team also found that the higher summer temperatures expected with ongoing climate change would worsen the impacts of this pollution.

smogThese researchers wanted to know more about the role of pollution from traffic and the industrial burning of fossil fuels in these deaths. To find out, they compared death rates in New Jersey between 2004 and 2009 to concentrations of fine particulates — meaning especially tiny, nano-size bits. They broke the information into different geographic areas, known as census tracts. Each tract includes about 4,000 people. Doing the study this way, the scientists were able to match death rates with local data on both air pollution and heat.

Pollution levels for each census tract came from NASA satellites that pass over every place on Earth every day. The scientists also used air pollution data from ground-based monitoring stations. These data had been collected by the U.S. Environmental Protection Agency.

“We could then look at how exposure to particulates changed from year to year and to see if they were associated with higher death rates. And they were,” says Schwartz. “So we think this has got to be a causal relationship. Nothing else could have affected it,” he argues.

The researchers shared their findings April 14 in Environmental Health Perspectives.

These were not ‘worst-case’ examples

New Jersey’s air pollution used to be worse, Schwartz notes. So seeing effects even now is significant, he says. If death rates are increasing at these pollution levels, he explains, then “these levels should be lowered.”

Indeed, these results add to the “evidence that particulate air pollution causes premature mortality,” says Brauer. This also suggests that reducing this pollution can improve health and save lives. And, he adds, “This is a problem we know how to solve.” Governments have already begun to do this in North America, Western Europe and Japan. The new findings, he says, “should support continuation of these efforts here and elsewhere.”

While all three studies looked at what’s happening in a single U.S. state, the scientists say these effects are also happening elsewhere. Wellenius and Schwartz also point out that the information from these studies can be used by local and national governments to prevent heat related illness and deaths anywhere and everywhere around the globe.

Power Words

(for more about Power Words, click here)

asthma    A disease affecting the body’s airways,which are the tubes through which animals breathe. Asthma obstructs these airways through swelling, the production of too much mucus or a tightening of the tubes. As a result, the body can expand to breathe in air, but loses the ability to exhale appropriately. The most common cause of asthma is an allergy. It is a leading cause of hospitalization and the top chronic disease responsible for kids missing school.

cardiovascular    An adjective that refers to things that affect or are part of the heart and the system of vessels and arteries that move blood through the heart and tissues of the body.

causality   (also causal relationship) The idea that one action makes another happen; that some result would never have happened if some particular thing didn’t trigger it.

census     An official count or survey of a population. A census tract is a specific geographic area where such a survey is done.

chronic     A condition, such as an illness (or its symptoms, including pain), that lasts for a long time.

climate    The weather conditions prevailing in an area in general or over a long period.

climate change    Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

combustion     The process of burning.

death rates       The share of people in a particular, defined group that die per year. Those rates can change if the group is affected by disease or other deadly conditions (such as accidents, natural disasters, extreme heat or war and other sources of violence).

Environmental Protection Agency (or EPA)     An agency of the federal government charged with helping create a cleaner, safer and healthier environment in the United States. Created on Dec. 2, 1970, it reviews data on the possible toxicity of new chemicals (other than food or drugs, which are regulated by other agencies) before they are approved for sale and use. Where such chemicals may be toxic, it sets rules on how much may be used and where it may be used. It also sets limits on the release of pollution into the air, water or soil.

epidemiology    Like health detectives, researchers in this field figure out what causes a particular illness and how to limit its spread.

fossil fuel     Any fuel — such as coal, petroleum (crude oil) or natural gas — that has developed in the Earth over millions of years from the decayed remains of bacteria, plants or animals.

global warming    The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.

heart attack       Permanent damage to the heart muscle that occurs when one or more regions of it become starved of oxygen, usually due to a temporary blockage in blood flow.

high blood pressure   The common term for a medical condition known as hypertension. It puts a strain on blood vessels and the heart.

mortality    Deaths. From mortal, meaning deadly

National Aeronautics and Space Administration, or NASA     Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It has also sent research craft to study planets and other celestial objects in our solar system.

ozone    A colorless gas that forms high in the atmosphere and at ground level. When it forms at Earth’s surface, ozone is a pollutant that irritates eyes and lungs. It is also a major ingredient of smog.

particulate matter (PM)    Pollution made up of particles, a complex mixture of extremely small particles and liquid droplets. Very fine PM, with particles 2.5 micrograms or smaller is considered particularly hazardous to health as it can enter the body easily.

pneumonia    A lung disease in which infection by a virus or bacterium causes inflammation and tissue damage. Sometimes the lungs fill with fluid or mucus. Symptoms include fever, chills, cough and trouble breathing.

premature mortality   Deaths that occur months to years earlier than would normally be expected.

respiratory   Of or referring to parts of the body involved in breathing (called the respiratory system). It includes the lungs, nose, sinuses, throat and other large airways.

smog    A kind of pollution that develops when chemicals react in the air. The word comes from a blend of “smoke” and “fog,” and was coined to describe pollution from burning fossil fuels on cold, damp days. Another kind of smog, which usually looks brown, develops when pollutants from cars react with sunlight in the atmosphere on hot days.

stroke   (in biology and medicine) A condition where blood stops flowing to part of the brain or leaks in the brain.

tract     A particular, well-defined area. It can be a patch of land, such as the area on which a house is located, or a large segment of a city or larger community. Or it can be a bit of real estate in the body. For instance, important parts of an animal’s body will include its respiratory tract (lungs and airways), reproductive tract (gonads and hormone systems important to reproduction) and gastro-intestinal tract (the stomach and intestines — or organs responsible for moving food, digesting it, absorbing it and eliminating wastes).

vulnerable    Describes those who are most susceptible or likely to be harmed.

Word Find (click here to enlarge for printing)


  • MS-ESS3-4
  • MS-ESS3-5
  • HS-ESS3-6


Journal : S. Soneja et al. Exposure to extreme heat and precipitation events associated with increased risk of hospitalization for asthma in Maryland, U.S.A. Environmental Health. Vol. 15, April 27, 2016, p. 57. doi: 10.1186/s12940-016-0142-z.

Journal : G.A. Wellenius et al. Current and projected heat-related morbidity and mortality in Rhode Island. Environmental Health Perspectives. Vol. 124, April 2016, p. 460. doi: 10.1289/ehp.1408826.

Journal : Y. Wang et al. Estimating causal effects of long-term PM2.5 exposure on mortality in New Jersey. Environmental Health Perspectives. Published online April 14, 2016. doi: 10.1289/ehp.1409671.

Further Reading

S. Ornes. “Bad for breathing.Science News for Students. March 8, 2013.

Learn more about climate change from NASA.

Video: University of British Columbia. Deaths linked to air pollution expected to rise.

Questions for "Heat sickness"