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Poison Ivy Itchier, More Plentiful With Warming, Study Says

Brian Handwerk
for National Geographic News
May 30, 2006
 
Global climate change may soon make our planet a much itchier place.

Rising levels of carbon dioxide—a so-called greenhouse gas that traps heat within Earth's atmosphere—can fuel booming poison ivy growth, a new study reports.

Even worse, the rash-inducing vines may become more potent.

Working in a Duke Univerity-owned forest near Chapel Hill, North Carolina, researchers used a system of carbon dioxide-pumping pipes to create atmospheric CO2 levels that were some 200 parts per million higher than the current norm.

Many global warming models predict that such levels will be a reality by 2050. (Related: "Global Warming Could Cause Mass Extinctions by 2050, Study Says" [April 12].)

Poison ivy growth surged some 150 percent in the carbon dioxide-rich forest plots.

Poison ivy afflicts countless people each year—more than 350,000 Americans alone are miserable enough to seek professional treatment.

Found in woody areas across North America, the plant also grows in Central America and parts of Asia, and has been introduced to Europe, Africa, Australia, and New Zealand.

About 80 percent of all people are allergic to poison ivy's sap or resin. Sufferers experience a red, bumpy, itchy, and sometimes blistering skin rash when they come into contact with urushiol—the plant's carbon-based active compound.

Unfortunately, the study also found that carbon dioxide-enhanced poison ivy boasts a stronger strain of urushiol, which may prove even more poisonous to humans.

"That was a bit of a surprise," said lead author Jacqueline Mohan, a postdoctoral scientist at the Ecosystems Center of the Marine Biological Laboratory in Woods Hole, Massachusetts.

"It was not actually producing more of the carbon compounds but producing a more poisonous form."

The six-year study's results were published in today's issue of the Proceedings of the National Academy of Sciences.

CO2 and the Fate of Future Forests

The forest setting at Duke allowed scientists to examine the impact of increased CO2 in a real-world environment beyond the walls of the lab.

Mohan explained that her team is researching how rising carbon dioxide levels may alter forest ecosystems.

"Woody vines [including poison ivy] are probably going to take off with increased atmospheric levels of CO2," she said.

Recent studies in temperate and tropical forests already report increases in these plants. Some scientists speculate that these changes are due to rising carbon dioxide levels.

The increased growth of woody vines could dramatically alter future forests—for instance, by choking new tree growth. Woody vines can grow over the tops of large trees "and certainly shade out juvenile trees," Mohan said. "Those [juveniles] are the trees you'd [normally] expect to be the forest of the future."

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