A changing climate also increases the likelihood of extreme weather events like heavy rainfall, which can exacerbate allergies from mold spores. Rotkin-Ellman cited the aftermath of Hurricane Katrina in New Orleans as an example of this. "It wasn't only dangerous levels of mold spores in homes, but all of the elevated levels of flooding created spores in the air as a whole," she said.
Stinging insects invade Alaska
Farther north, the shifting climate is proving to be a boon for stinging insects. Jeffrey Demain, director of the Allergy, Asthma & Immunology Center of Alaska, noted that America's northernmost state saw a 46 percent increase in insect stings, with some parts of the state suffering increases as high as 626 percent. Two insect fatalities were also recorded in 2006. Alaskans' "likelihood of exposure and interface with stinging insects is increasing," Demain said.
This comes largely from warmer winter temperatures leading to more snowfall, since Alaskan winters often reach the point where it's too cold to snow. The snow helped insulate insect dwellings, and as a result, more stinging insects survived the winter and expanded their ranges. Now people are finding out the hard way whether they are allergic to stings.
Birch trees, a major pollen source in Alaska, have also benefited from the recent climate changes. "Not only is there a likelihood we are insulating the insect queen's hibernaculum, the snowpack also protects the trees and it protects the roots," said Demain. "As the permafrost melts, we're seeing trees grow where there have never been trees."
Though Alaska's allergy predicament is relatively unusual in the United States, there are analogues in other parts of the world, according to Demain. "I think our allergy-related issues are correlated more with what you'd see in Sweden, just based on the latitude," he said.
Researchers in Europe have also observed allergy changes from the climate. Tim Sparks at the Institute for Advanced Study at the Technical University of Munich co-authored a paper earlier this month in the journal PLoS ONE that showed that increasing carbon dioxide is a bigger allergen driver than rising temperatures.
However, on shorter time frames, changes in weather patterns can alter allergic risks. "Heavy rainfall would tend to ground pollen," said Sparks. "High winds will transmit it further distances." Over the long term, Sparks expects pollen levels to continue to rise.
Fewer places to hide
Human vulnerability is the other side of the allergy problem. Asthma and associated allergy rates have risen all over the world, and scientists have yet to pin down a cause. "Everybody is scratching their heads," said Stephen Apaliski, an allergist and author of "Beating Asthma: 7 Simple Principles." "We're definitely seeing more cases of asthma. We seem to be having some worse cases of asthma, as well. We certainly know that the prevalence has risen over the past 20 years."
In addition, allergens are now so ubiquitous, it's hard to find a safe place for sensitive eyes, skin and throats. "There is almost nowhere you can really go to get away from this," said Apaliski. He noted that physicians in the past recommended that people with allergies move to drier climates, but even those areas are increasingly dusted with pollen.
Allergies can be especially troublesome in urban areas, where allergens coupled with pollution can form a potent health threat. "That synergy is really worrisome because of how many people in this country have asthma and rising rates of asthma," said the Natural Resources Defense Council's Rotkin-Ellman. "Ozone and pollen together are a very dangerous mixture." This will lead to more severe allergic reactions and more hospital visits.