The health of millions of children worldwide is threatened by global warming and air pollution. The world's poorest kids are at highest risk, experts say, of getting caught in a growing asthma epidemic.

In a report released Thursday, researchers at the Harvard Medical School's Center for Health and the Global Environment said the warming global climate is releasing more allergens into the air.

Once floating in the sky, the allergens combine with pollutants such as ozone and soot, resulting in a recipe for a health crisis.

"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," Harvard's Dr. Paul Epstein told a news conference.

Hardest hit will be children from "poor and minority groups in the inner cities" where the effects of automobile emissions are worst.

"These children get hit with a powerful one-two punch: exposure to the worst air quality problems and the additional allergen exposure arising from global warming," Harvard School of Public Health researcher Christine Rogers said in a statement.

According to the report, "Inside the Greenhouse: The Impacts of CO2 and Climate Change on Public Health in the Inner City," the effects can already be seen among American preschoolers.

The rate of asthma among kids age 3 to 5 grew by 160 per cent between 1980 and 1994 -- more than double the rate reported among the general population.

Figures like that, experts say, should shock people.

"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," Rogers said.

Something can be done to help those most at risk of this looming epidemic, Epstein told reporters.

"Green" buildings with rooftop gardens, improved public transportation and promotion of hybrid vehicles that rely less on fossil fuels would all reduce the exacerbating factors, he said.

Asthma is a chronic lung condition characterized by sometimes severe difficulty breathing. Common symptoms include wheezing, coughing, shortness of breath and chest tightness

According to the Canadian Lung Association, approximately one in 10 children in Canada suffer from asthma. About 20 children and 500 adults die of the disease each year.