They released a report showing that as the climate gets warmer, allergens such as pollen and mold will flood the air, interacting with urban pollutants such as ozone and soot to fuel an already growing epidemic of asthma.
\"It is affecting the trees, the molds, the subsurface organisms,\" Dr. Paul Epstein of Harvard Medical School\'s Center for Health and the Global Environment, told a news conference.
\"The combination of air pollutants, aeroallergens, heat waves and unhealthy air masses -- increasingly associated with a changing climate -- causes damage to the respiratory systems, particularly growing children, and these impacts disproportionately affect poor and minority groups in the inner cities,\" the report reads.
The report finds that asthma among U.S. preschool children, age 3 to 5, grew 160 percent between 1980 to 1994.
\"This is a real wake-up call for people who 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 a meaningful way,\" said Christine Rogers, a senior research scientist at the Harvard School of Public Health.
\"The problem is here today for these children and it is only going to get worse.\"
Rogers, Epstein and the American Public Health Association worked together on the report.
Most climate experts agree that the world is becoming steadily warmer, and that human activity is much to blame. Burning fossil fuels such as coal and gas releases carbon dioxide into the air.
The carbon dioxide forms a kind of invisible blanket that traps the sun\'s radiation.
While average temperatures warm, the effects are not predictable and even. Storms may become more severe and some areas may get colder weather.
The report finds that in some regions, winter is ending weeks earlier than before, and plants are releasing their pollen earlier than ever, accelerating the hay fever season.
Pollen and fungal spores can worsen asthma, a serious medical condition whose symptoms include shortness of breath, cough, wheezing, chest pain or tightness.
The Centers for Disease Control and Prevention said nine million U.S. children have been diagnosed with asthma and more than 4 million have had an asthma attack in the past 12 months. It says 4,487 people died from asthma in 2000, most of them adults.
Asthma affects blacks more than any other group and affects 16 percent of children from poor families as opposed to 11 percent of children living above the poverty line.
The CDC also says 9 million U.S. children were reported with respiratory allergies in 2002.
The report makes clear links among asthma, allergies and urban air pollution.
\"Rising levels of carbon dioxide, in addition to trapping more heat, promote pollen production in plants, increase fungal growth and alter species composition in plant communities by favoring opportunistic weeds like ragweed and poison ivy,\" the report reads.
\"Diesel particulates help deliver and present pollen and mold allergens to the immune system in the lungs,\" it adds.
\"The good news is we can do something about this,\" Epstein said. \"Green\" buildings with roof gardens to keep them cool and insulation to keep heat from leaking would help, as would improving public transport and encouraging the use of hybrid vehicles that rely less on fossil fuels.