Experts say global warming may be bad for asthma sufferers because of longer plant growing seasons and signs that weeds scattering vast amounts of pollen are conquering new territory.

“In the United States the incidence of asthma is up nearly four times since 1980,” said Paul Epstein, Associate Director of the Center for Health and the Global Environment at Harvard Medical School.

“No one has really been looking at the aerobiology dimension (such as pollen). But I think it helps account for it,” he said. Other triggers range from mites and dust to viruses and food.

And any warming may make things worse, he told Reuters.

A draft U.N. climate report due for release on April 6 says that plant growing seasons have become longer because of a warming trend blamed on human burning of fossil fuels.

It says that the world’s agricultural potential is likely to rise, especially in temperate countries, if temperatures rise by up to 3 Celsius (5.4 Fahrenheit). Above that level, farm potential will fall in all regions. Source