Dead heat: the health consequences of global warming could be many

Science News, July 3, 2004 by 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[degrees]F) and remained high for weeks.

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. Averk age 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.