Watery eyes, runny noses and puffy faces will abound this year as a warm winter, human development and climate change converge to create a brutal allergy season that will likely get worse for years to come, according to experts.

Plants like ragweed are in pollen overdrive from very favorable weather, while stinging insects like yellow jackets and hornets are findings new homes farther north. More people are becoming susceptible to allergies over time as pollen seasons are getting longer.

This increases risks for people who are already sensitized and threatens those with respiratory problems. The spread of allergies can have tremendous economic consequences as patients with reactions fill clinics and emergency rooms and as afflicted workers stay home.

Allergy symptoms result from the body's immune system overreacting to a given substance, known as an allergen. The symptoms range from mild, such as itchy eyes and hives, to life-threatening when airways swell shut. These conditions already afflict 60 million people in the United States, according to the Asthma and Allergy Foundation of America, and annually cost $21 billion.

Though most allergies can be controlled and treated, public health officials have found that an increasing number of people are adversely reacting to pollen, dander, dust and insects. As the climate shifts, these allergens are expanding to new areas, and previously unexposed people are now reaching for antihistamines.

Ragweed is one of the most common allergen sources and has spread in part due to human activity. "There is a growing body of science showing warming temperatures and carbon dioxide levels cause increases in pollen from ragweed," said Miriam Rotkin-Ellman, a public health scientist at the Natural Resources Defense Council. The plant's pollen is most dangerous from when it flowers in midsummer until when it's killed by the first frost in the fall.

Other pollen sources, like trees, peak in the spring, while grass pollen peaks in the early summer. Warming temperatures have lengthened the risk period for these plants up to several weeks. "It means more misery for allergy sufferers because you're looking at a longer time for exposure to pollen," Rotkin-Ellman said. "All of these factors combine to create a really terrible allergy season."

A rising atmospheric carbon dioxide concentration is also important because it nourishes plants, and fast-growing pollen producers like ragweed are often the quickest to avail themselves of its increasing abundance.

The growing potency of weeds and mold
"When we look at weeds that are associated with pollen, those changes are having a disproportionate effect on their ability to grow and their ability to produce pollen," said Lewis Ziska, a plant physiologist with the U.S. Department of Agriculture's Agricultural Research Service. He noted that, geographically, these patterns change with latitude, with northern areas of the country showing the most drastic increases in environmental allergens.

Already, parts of the country have broken allergy records. In New Jersey, officials observed the highest pollen levels ever recorded in February this year. "I've never seen that in 25 years of my work in this area," said Leonard Bielory, an attending physician and allergist at the Robert Wood Johnson University Hospital and a professor at Rutgers University's Center for Environmental Prediction. "I told people before the year began that it's going to be a horrendous year."

Bielory co-authored a paper with Ziska last year in the Proceedings of the National Academy of Sciences documenting how the ragweed season has grown up to 27 days in parts of the country since 1995. "It's clear that just in New Jersey over the past 20 to 25 years, there's been an increase of five to seven days for pollen," he said.

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.

As average temperatures rise, allergies will continue to rise, but only up to a certain point, according to Rutgers' Bielory. Eventually, pollen counts will hit a plateau and may even decline. "It cannot continue on a linear scale," he said. "If heat goes up to a certain temperature, plants will die. It will hit a breaking point."

USDA's Ziska said increased carbon dioxide levels will make allergenic weeds more difficult to control with herbicides. The solution is instead to make the environment more hospitable to native plant species and less prone to weed infestations, according to Steven Apfelbaum, a senior ecologist with Applied Ecological Services Inc., an environmental restoration firm. "Plan A would be to restore the land and the ecosystems so they are healthy and they can tolerate and are not as vulnerable to the unpredictable weather that has been tossed at them," he said.

For people with allergies, the best way to prevent reactions is to stay informed. Bielory is developing iPollenCount, an iPhone app to track pollen. Using this information, people can schedule their outdoor activities to minimize their exposure on high-risk days. More broadly, Bielory said people need to take steps to minimize their emissions, not only to curb short-term pollution, but to slow the long-term climate changes that are driving environmental health risks.

Still, there is no rapid way to reverse these allergy trends, and the risks will continue to increase for the foreseeable future. "My perspective is that we can mitigate all we want but have to learn to adapt and, more so, prepare," said Bielory.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500