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Dead Heat
The health consequences of global warming could be many

Sid Perkins

If the mere thought of global warming makes you break out in a sweat - an unpleasant consequence, to be sure - just wait until the heat gets here in earnest. Some time this century, lengthy heat waves like the one that killed thousands in Europe last summer may become the summer norm. Diseases now found only in the tropics may broaden their range, and ones that currently threaten subtropical or temperate regions for only short periods each year may afflict residents of those areas for longer durations. Noxious gases and other airborne irritants could also increase with global warming, significantly heightening the toll of lung diseases.

Portraits of doom wrought by long-term climate change are familiar by now, but new studies suggest that adverse health effects related to global warming aren't just a theoretical concern for the distant future. If the record-setting heat waves that beset Europe and the United States in recent years are early symptoms of long-term climate change, then global warming has already claimed tens of thousands of lives. Also, scientists have already discerned increases in asthma and other respiratory ailments among inner city youths, a trend that will probably accelerate as atmospheric concentrations of carbon dioxide continue to rise and the planet's climate warms even further.

Heat wave

Last summer, a region of high atmospheric pressure sat over western Europe and blocked the flow of rain-bearing low-pressure systems that typically arrive from the Atlantic Ocean. As a result, much of the continent experienced an extended period of unusually hot, dry weather. Switzerland saw its hottest June in 250 years, with the average temperatures in Basel hovering at 29.5 degrees C (85 degrees F), about 5.9 degrees C above normal. Temperatures in France soared to 40 degrees C (104 degree sF) and remained high for weeks.


HOT TIMES. Average temperatures in the summer of 2003 approached 5 degrees C above normal in some places. A lengthy heat wave killed an estimated 30,000 Europeans.

NOAA/National Climatic Data Center

France's National Institute of Health and Medical Research estimated that almost 15,000 more people died in that country in August 2003 than would be expected for an average August. Demographers in Italy estimated an excess death toll of more than 4,000 residents in that country's 21 largest cities. In all, some scientists suggest that Europe's 2003 heat wave claimed more than 30,000 lives, making it the continent's largest natural disaster in 50 years.

Climate projections suggest that last year's heat wave might become the norm for Europe before this century ends. Martin Beniston of the University of Fribourg in Switzerland used global and regional climate models to estimate what summers would be like between 2071 and 2100. Specifically, he looked at the United Nations' International Panel on Climate Changes' A2 scenario, in which total atmospheric concentrations of carbon dioxide, methane, chlorofluorocarbons, and other greenhouse gases reach the equivalent of about 800 parts per million, about twice those in the air today.

A major driving force of global warming is the increased atmospheric concentration of carbon dioxide generated by the burning of fossil fuels in automobiles and other vehicles, power plants, and industrial furnaces. The gas wields its greenhouse effect by intercepting heat that otherwise would escape from Earth into space. The warming effect increases other air pollutants, such as ground-level ozone, by accelerating chemical reactions in the atmosphere.

Carbon dioxide concentrations were about 280 ppm when the Industrial Revolution began in the mid-1850s, and they've been on the rise ever since. Concentrations increased about 1.8 ppm per year through the 1990s and are now rising about 3 ppm each year. On average, the atmosphere now holds about 379 ppm of the greenhouse gas.

Results of Beniston's end-of-century climate simulations, published in the Jan. 28 Geophysical Research Letters, show a strong trend of summer warming across much of Europe. Average temperatures for June, July, and August across a broad swath of central Europe by the end of the century will increase about 4 degrees C. Many areas of southwestern France and the Iberian Peninsula will see average summertime temperatures rise about 6 degrees C. Some regions along the Mediterranean and in eastern Europe will experience as many as 60 more days above 30 degrees C than they do now.

Beniston's analyses suggest that in Basel, the average summertime temperature for the last 3 decades of the 21st century will be 28.8 degrees C, just slightly less than last summer's average of 29.5 degrees C. Daily high temperatures in the city will exceed 30 degrees C even more often than they did last year.

These results are bolstered by a similar analysis by another team, published in the Jan. 22 Nature, which shows average summertime temperatures in northern Switzerland rising about 4.6 degrees C by the end of the century. If last year's heat wave indeed becomes just an average summer in years to come, fully half the summer seasons at the end of the century will be hotter and drier than the one that Europeans endured in 2003, says Christoph Schar of the Swiss Federal Institute of Technology in Zurich.

Although heat waves are one of nature's greatest killers, many of the factors that contribute to the resulting deaths are social rather than environmental (see "Easing the Heat," below). In France, for example, the heat wave struck during August, a traditional vacation period when many residents head for the countryside and doctors are hard to find. Many of the country's victims were elderly and either alone at home without air conditioning or confined to crowded hospitals or nursing homes. With foreknowledge of growing summertime heat dangers, national, regional and local officials can take steps to look after their most vulnerable citizens. In other words, annual death tolls on the order of what occurred in Europe last year aren't inevitable.

Moving on up

Only a small portion of the dangers posed by increasing heat will be assuaged by better air conditioning. Diseases once sequestered to the tropics will be moving with the heat to higher latitudes.

A site's prevailing environmental conditions can dictate which diseases are common there. Conditions must be hospitable for the microorganism that causes the disease, the host, and any creatures that take part in transmitting the disease. As today's climate zones move toward higher latitudes in a warming world, so will many of the potentially disease-bearing creatures that inhabit them (SN: 3/8/03, p. 152).

Take malaria, a disease that's caused by the Plasmodium falciparum parasite and transmitted to people by the bite of infected mosquitoes. Every 30 seconds or so, malaria claims a life somewhere in the world, mainly in tropical regions in which the mosquitoes and the parasites they carry can thrive.

Climate models suggest that the warming expected later this century will render many new regions susceptible to malaria, says Tracey Holloway of the University of Wisconsin–Madison. By the 2080s, according to one study, residents of some previously malaria-free areas, such as the United States' Pacific Coast, southern Scandinavia, and some regions of Siberia, might be at risk of malaria from 1 to 3 months each year. In other areas, such as eastern China, central Europe, and the Ohio River Valley, environmental conditions might become ripe for the transmission of malaria for up to 5 more months each year then than they are now.

Sophisticated computer models that can estimate future environmental conditions become even more powerful tools when they're combined with epidemiological data. With judicious assumptions about trends in population growth, land use, and industrial pollution, researchers can assess the possible health consequences of a warmer world.

Two atmospheric pollutants that substantially affect human health are fine particulate matter - ground-level ozone and airborne particles 2.5 micrometers in diameter or smaller that can be inhaled deep into lungs. Higher-than-normal concentrations of both pollutants are associated with increased numbers of emergency room visits, hospital admissions, and deaths from lung diseases, says Patrick L. Kinney of Columbia University.

As part of the New York Climate and Health Project, Kinney and his colleagues are using a set of computer models to estimate the health effects of the coming century's climate change in the New York metropolitan area, a 33,600-square-kilometer region that's home to 21 million people. One model predicts concentrations of ozone and other pollutants, another simulates coming changes in land use as the population grows, and yet another estimates the number of deaths associated with increased pollution and elevated temperatures. For example, industrial emissions and other atmospheric constituents react to form ozone and other pollutants more quickly at warmer temperatures.

Under a moderate climate-change scenario, the models project that increased temperatures in the New York metropolitan area in the 2050s could result in as many as 1,700 heat-related deaths each year. That's about double the number that occurred in a typical year during the 1990s, says Kinney. Most of those deaths are expected in the center of New York City and downwind of it on the western tip of Long Island. Kinney presented the group's findings at a press conference in New York City on June 25. Previous research suggests that the New York metro region might see about 50 additional deaths each year in the 2050s from increased concentrations of ground-level ozone, a jump of about 4 percent.

In the future, says Kinney, the project's researchers will refine their models, look at the effects of pollutants on more cardiopulmonary ailments than they've examined so far, and estimate the health effects during the 2020s and the 2080s.

It's heeeere

Some studies suggest that when it comes to the downside of global warming, the future is now. Consider asthma, which affects about 16 million U.S. adults and a growing number of children. Each year, it costs about $3.2 billion to treat the disease in people under the age of 18, says Paul R. Epstein of Harvard Medical School's Center for Health and the Global Environment in Boston. He and his Harvard colleague Christine Rogers recently published a report that outlines how climate change is making its mark on public health - particularly in inner cities, where a confluence of factors places children at higher-than-normal risk.


GRAINY IMAGE. When people inhale grains of pollen that are tainted with diesel soot, the material is more likely to aggravate asthma than are pollen grains alone.

R. van Hout and M. Koontz, Johns Hopkins Univ.

Among those factors are increased concentrations of pollen and mold spores that result from carbon dioxide's fertilizing effect on plants. Although average atmospheric concentration of carbon dioxide around the world is 379 ppm, some studies have found concentrations ranging up to 600 ppm in cities such as Phoenix, New York City, and Baltimore. Studies have indicated that doubling atmospheric concentrations of carbon dioxide boost ragweed growth by 10 percent and its pollen production by 60 percent.

Although pollen and mold spores don't cause asthma, they do aggravate the condition. Furthermore, says Rogers, some pollutants in city air can make these biological products even more noxious than usual. For example, pollen and spores readily attach to particles of diesel exhaust, which people then inhale. Substances in the exhaust seem to sensitize lung tissue to the pollen, thereby causing more respiratory distress than would occur if only the pollen were inhaled, says Rogers. Add elevated concentrations of ozone and you have the prime ingredients for an asthma attack.

Because children typically breathe faster than adults do, they're exposed to more of the noxious gases and particles. More than one-fourth of the children in Harlem have asthma, a much higher proportion than in most other areas of the United States, says Epstein.

"This [study] is a real wake-up call for people who mistakenly think global warming is only going to be a problem way off in the future or that it has no impact on their lives in any meaningful way," says Rogers. "The problem is here today for these [urban] children, and it is only going to get worse."


Easing the Heat
Chicago experiences show that hot spells can be less deadly

Heat waves are among nature's greatest killers and one of nature's unrecognized hazards, says Erik Bowles of Kansas State University in Manhattan. Heat waves claim more victims than all other weather events combined, he notes. Since 1991, heat waves have killed an average of 235 U.S. residents each year, while floods claimed 86, tornadoes took 59, and lightning killed 53 people.

Most often, says Bowles, the victims of heat waves live in inner cities, have lower-than-average incomes, and are sick or elderly. Because heat waves seem less threatening than more-dramatic weather phenomena, such as tornadoes or thunderstorms, people don't feel an immediate need to run for cover and therefore adopt a "wait-it-out" mentality, he notes.

Heat waves strike broad regions, rather than the limited swaths directly influenced by thunderstorms or tornadoes. Yet because heat waves are more easily predicted and often build slowly, many deaths that result from them are preventable, says Karen E. Smoley-Tomic of the University of Alberta in Edmonton.

The disparate results of two recent heat waves that struck Chicago seem to bolster that contention. Heat-related deaths during the first scorcher in July 1995 claimed 739 Chicago residents—more than double the number that died in the great Chicago Fire of 1871. Most victims were elderly and poor, lived in the heart of the city, and either had no air conditioning or couldn't afford to turn it on. In some areas of the city, fear of crime deterred some people from opening their windows. Statistical analyses later showed that the residents at greatest risk for dying lived alone and were socially isolated.

After 1995, Chicago instituted a citywide plan to check on elderly residents and provide access to air-conditioned areas in schools. Those plans appear to have paid off in 1999, when a midsummer heat wave claimed only about 110 Chicagoans. The peak heat and humidity during that year's heat wave were slightly lower than those experienced in the 1995 event, but the 1999 hot spell lasted more than a week longer, says Michael A. Palecki, a climatologist at the Illinois State Water Survey in Champaign. Although it's tough to directly compare the two events, he notes, "it's pretty clear that the city's response to the 1999 heat wave saved hundreds of lives."



It is very disappointing that this article has not a word about any disagreement surrounding the health and related consequences of global warming, let alone of any disputes about its very likelihood.

Tibor R. Machan
Orange, CA

The article asserts that malaria and other tropical diseases will migrate northward with global warming. This ignores the fact that malaria was common in many parts of the United States 100 years ago but is now virtually unknown, even in south Florida. Also, there were several major epidemics of yellow fever in midlatitude American cities back then. Malaria and yellow fever, like plague, typhoid, and cholera, are basically social, not climatic, afflictions.

Douglas Lilly
Kearney, NE

In the typical "correct science" harangue of today, all the possible bad effects are emphasized (deadly summer heat waves), none of the possible good effects are even mentioned (CO2 is a primary plant food), and nothing at all is hinted about the state of computer models used to predict such "imminent" (100 years hence) cataclysms. I say shame on Science News.

Owen W. Dykema
Roseburg, OR

Although carbon dioxide indeed has a fertilizing effect on plants, many studies have found that that effect often doesn't last because the soil soon becomes exhausted of other nutrients. Also, one long-term study of rice yields in the Philippines suggests that a temperature increase of just 1°C will reduce harvests by as much as 10 percent (SN: 7/10/04, p. 29).—S. Perkins


Beniston, M. 2004. The 2003 heat wave in Europe: A shape of things to come? An analysis based on Swiss climatological data and model simulations. Geophysical Research Letters 31(Jan. 28):L02202. Abstract.

Bowles, E., and J. Harrington. 2004. Heat waves: An under-recognized hazard. Annual Meeting of the Association of American Geographers. March 18. Philadelphia.

Epstein, P.R., and C. Rogers, eds. 2004. Inside the Greenhouse: The Impacts of CO2 and Climate Change on Public Health in the Inner City. Boston: Harvard Medical School, Center for Health and the Global Environment. Available at

Holloway, T., and G. McKinley. 2003. Overview of issues in health, air pollution, and climate. American Geophysical Union meeting. Dec. 8–12. San Francisco. Abstract.

Kinney, P.L., et al. 2003. Health impacts of air pollution under a changing climate. American Geophysical Union meeting. Dec. 8–12. San Francisco. Abstract.

Palecki, M.A., S.A. Changnon, and K.E. Kunkel. 2001. The nature and impacts of the July 1999 heat wave in the Midwestern United States: Learning from the lessons of 1995. Bulletin of the American Meteorological Society 82(July):1353–1368. Abstract.

Schär, C., et al. 2004. The role of increasing temperature variability in European summer heatwaves. Nature 427(Jan. 22):332–336. Abstract.

Smoyer-Tomic, K.E. 2004. Women's roles, women's risk: A genderized meta-analysis of heat wave mortality. Annual Meeting of the Association of American Geographers. March 18. Philadelphia.

Further Readings:

Perkins, S. 2004. Warmer climate, decreased rice yield. Science News 166(July 10):29. Available at Science News.

______. 2003. Spring forward. Science News 163(March 8):152. Available at Science News.


Martin Beniston
Department of Geosciences
University of Fribourg
Chemin du Musee 4
CH-1700 Fribourg

Erik Bowles
Kansas State University
Department of Geography
118 Seaton Hall
Manhattan, KS 66506-2904

Paul R. Epstein
Center for Health and the Global Environment
Harvard Medical School
401 Park Drive
Boston, MA 02115

Tracey Holloway
University of Wisconsin, Madison
Gaylord Nelson Institute for Environmental Studies/SAGE
1710 University Avenue, Room 201A
Madison, WI 53726

Patrick Kinney
Columbia University
Mailman School of Public Health
Department of Environmental Health Sciences
60 Haven Avenue, B-1
New York, NY 10032

Michael A. Palecki
Illinois State Water Survey
114 WSRC
MC 674
2204 Griffith Drive
Champaign, IL 61820

Christine Rogers
Harvard School of Public Health
677 Huntington Avenue
Boston, MA 02115

Christoph Schär
Atmospheric and Climate Science
Swiss Federal Institute of Technology
ETH Zurich
Winterthurerstrasse 190
8057 Zurich

Karen E. Smoyer-Tomic
University of Alberta
Department of Earth and Atmospheric Sciences
3-92, Tory, HM
Edmonton, AB T6G 2H4

From Science News, Volume 166, No. 1, July 3, 2004, p. 10.