If you found yourself sneezing and rubbing your itchy eyes more often through the fall hay fever season, put the blame on climate change.
Researchers at Children’s Mercy Hospital say the extra carbon dioxide we’re putting into the air, combined with warmer temperatures, have ragweed pumping out enormous amounts of pollen.
Daily pollen counts taken by the hospital show that the total amounts of ragweed pollen collected annually have been two to three times higher in recent years than they were in the late 1990s. Ragweed pollen seasons also have been running longer, often extending into late October or even mid-November when they used to end by mid-October.
“The bottom line is that’s plenty of ragweed to make people miserable,” said Charles Barnes, the Children’s Mercy biochemist in charge of calculating the hospital’s daily mold and pollen counts from instruments on the hospital’s roof. Barnes and his research colleagues reported their findings Sunday in Houston at the annual meeting of the American Academy of Allergy, Asthma & Immunology.
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It’s not just around Kansas City that people are suffering more from hay fever. A recent USDA study found that ragweed pollen seasons have been getting longer throughout central North America.
Ragweed pollen is the offending allergen for about three out of four hay fever sufferers.
But scientists worldwide have found pollen seasons have been lengthening and pollen volumes increasing for a variety of other plants that cause misery for people with allergies. One researcher who applied computer models to data from pollen collection sites in the United States and Europe has predicted that average global counts of birch tree pollen will more than double between 2000 and 2040; by 2100, there could be eight times as much birch pollen in the air.
In 2006, Barnes and other Children’s Mercy researchers reported that during the previous decade the oak pollen season in Kansas City had been starting, on average, a half day earlier each year.
Barnes was somewhat skeptical then about whether climate change was the cause. Day-to-day weather is highly variable, and the changes he was seeing could have been happening by chance, he figured. For example, rain that falls at one period in a plant’s life may promote its growth and turn it into a prodigious pollinator; rain falling at another time can wash that plant’s pollen from the air.
But now, with another decade’s worth of data, Barnes is convinced that global warming is the culprit.
“It’s the explanation that fits best at this point,” he said. “The data … are pretty convincing.”
Scientists say global warming is being caused by the enormous amount of carbon dioxide and other gases that cars, factories and power plants release into the atmosphere. The gases create a greenhouse effect, warming the Earth by keeping the sun’s heat from escaping through the atmosphere.
Research suggests that it’s both the warming and the extra carbon dioxide that are driving pollen production higher.
Carbon dioxide, along with water and sunlight, are the essential ingredients that fuel plant growth. Ragweed grown under laboratory conditions in a high-carbon dioxide atmosphere not only produce more pollen, but the pollen is more potent at triggering allergic reactions, studies by USDA research plant physiologist Lewis Ziska have found.
In a real world test, Ziska placed plant beds seeded with weeds in urban, suburban and rural settings. In the urban location, traffic kept carbon dioxide levels higher and heat-absorbing buildings raised temperatures.
“To our surprise, it made a huge difference how quickly the (ragweed) grew,” Ziska said.
The urban ragweed flowered earlier and grew to be six to 10 times the size of the rural plants, he said. “It was just phenomenal.”
Ziska also recruited 11 pollen collection stations, including the one at Children’s Mercy Hospital, to study the long-term effects of global warming on ragweed growing seasons. The stations, lined up north to south from Saskatoon, Canada, to a suburb of Austin, Texas, contributed data from 1995 to 2013.
The greater the distance from the equator, the greater the effect that atmospheric carbon dioxide has on increasing temperatures. So pollen seasons would be expected to increase more among the northern collection stations.
And generally, that is what Ziska found.
Over the years of the study, the ragweed pollen season lengthened by an average of 27 days in Saskatoon, 21 days in Minneapolis, 18 days in Kansas City and 10 days in Rogers, Ark.
“What you’re seeing there is the climate change, the warming effect,” Ziska said.
The effect on people may be equally dramatic. In 1970, about 10 percent of the U.S. population suffered from hay fever. By 2000, the number had risen to 30 percent, studies show.
“I have no shortage of job security. Hay fever is stronger than ever,” said Children’s Mercy allergist Jay Portnoy, who collaborated with Barnes on the new ragweed study.
At the Children’s Mercy allergy clinic, hay fever patients tend to be sicker than they used to be, Portnoy said. More clogged noses, more sneezes, more itchy, runny eyes.
“We used to stop seeing (hay fever) patients in late September, early October; now seeing them well into October is not unusual,” he said.
One of those Children’s Mercy patients is 15-year-old John Walker of St. Joseph. He is severely allergic to ragweed, enough that he was hospitalized several times when his hay fever triggered asthma attacks that left him gasping for air.
New medications have eased his symptoms enough to allow him to play on his high school football team. But a few years ago, John started noticing that his hay fever was worsening. Doctors at the hospital explained to him that hay fever seasons were growing worse and getting longer.
“My symptoms showed it,” he said.