Higher temperatures over the coming decades are expected to cause more smoggy days and heat waves, contributing to a greater number of illnesses and deaths in the United States, according to international climate scientists.Severe heat waves -- characterized by stagnant masses of warm air and consecutive nights with high minimum temperatures -- will intensify in the United States and Canada, according to the data on North America released Monday by the United Nations Intergovernmental Panel on Climate Change.
Southern California, the Southwest and the upper Midwest are already experiencing drought. Late in the century, in Los Angeles, the number of heat wave days is projected to increase from 12 days a year to between 44 and 95 days, the report said. The number of heat wave days in Chicago is expected to increase by 25 percent.
Just how much people and ecosystems suffer in North America, scientists reported, depends on how well greenhouse gases are controlled. And, the scientists cautioned, it depends on how well they plan for and try to prevent the damage.
"Without increased investments in countermeasures, hot temperatures and extreme weather are likely to cause increased adverse health impacts,'' including effects from heat, storms, pollution and infectious disease, the report said.
Adding to the problem is that the Baby Boomer population is aging as global warming worsens, increasing the number of people most at risk of dying in heat waves.
Global warming is already affecting people's health, said Kristi Ebi, an epidemiologist from Virginia and lead author of a chapter on human health written for the international science panel.
People will eventually better respond to heat waves with health care system improvements. They'll even adjust physiologically to warmer temperatures.
"It's while all of this is changing when you have high health impacts. And that could be in the next few decades,'' Ebi said in an interview.
The report singled out other health effects related to global warming, including:
-- More smog.
Warmer temperatures lead to greater concentrations of ground-level ozone, which forms on hot, sunny days when pollution from cars and other sources mix. Smog can damage lung tissue, increasing respiratory and heart disease and death. Even modest increases in smog can cause asthma in children.
"Ozone occurs more rapidly at higher temperatures, and emissions of the pollutants that form ozone can go up,'' said Patrick Kinney, associate professor of environmental health sciences at Columbia University. His studies were also cited in the international document.
"Just due to climate change, we expect ozone to get a little bit worse. That should have adverse consequences for human health,'' Kinney said.
Smog-related deaths from climate change are projected to increase by about 4.5 percent from the 1990s to the 2050s, according to studies at Columbia and Johns Hopkins universities. A scientist at Yale University, Michelle Bell, looked at the 50 largest cities in eastern United States and found that the health-alert days would go up by 68 percent over the next decades.
-- Spread of illnesses, disease and allergens.
High temperatures perpetuate malaria and other mosquito-borne diseases in the tropics. As global warming occurs, the mosquitoes can expand their range to higher elevations and northward.
William Reisen, a research entomologist at UC Davis, said mosquitoes -- and the parasites in the mosquitoes -- are beginning to exploit highland habitats that were once too cold for them.
The mosquitoes that carry the disease are already in the United States, Reisen said. But the U.S. public health effort, particularly in California, helps prevent infections because of the aggressive system to control mosquitoes, he said.
In a 2006 paper on West Nile virus in Illinois, the Dakotas, Colorado and Idaho, Reisen reported that higher temperatures make it easier to transmit the illness.
"As the virus moved westward at northern latitudes, it tracked abnormally warm summers,'' he said.
Currently, Lyme disease is limited by cold temperatures in the north that stave off the movement of the diseases-carrying tick. Studies have found that the northern range limit could shift north by 200 kilometers by the 2020s and 1,000 kilometers by the 2080s.
Pollen, another air contaminant, is likely to increase as temperatures and carbon dioxide levels rise. A doubling of the atmospheric carbon dioxide levels stimulated ragweed-pollen production by more than 50 percent, a study showed. In another, ragweed grew faster, flowered earlier and produced significantly more pollen in urban locations.
-- Food- and water-borne diseases.
A study of all water-borne disease reported in the United States between 1948 and 1994 found that two-thirds of the cases were preceded by heavy rainfall, according to author Jonathan Patz, associate professor at the University of Wisconsin.
Climate-change projections show an increase in the intensity of rainstorms, which create opportunities for pathogens to move around.
Under a grant from the U.S. Environmental Protection Agency, Patz is studying the effects of climate change on the Great Lakes region, looking at heavy precipitation and beach closures due to water contamination.
Ebi said a rise in salmonella has been linked to higher temperatures. Studies in Canada, Europe and Australia have shown a correlation between rising temperature and cases of salmonella, she said.
"Unless we do better about food-handling practices and other factors that lead to salmonella, rising temperatures would lead to more cases.''
E-mail Jane Kay at firstname.lastname@example.org.
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