More Pernicious Poison Ivy

When exploring the outdoors, many children are taught the mantra, "leaves of three, let it be"--referring, of course, to poison ivy. With climate change, that caveat could become even more important.

In a six-year study conducted at the Free-Air CO2 Enrichment area in Duke Forest, scientists found that, as atmospheric levels of carbon dioxide rise, poison ivy will likely grow larger--and more allergenic.

Previous research had demonstrated that elevated levels of carbon dioxide can increase the growth of other plants like honeysuckle and kudzu. In the Duke study, researchers compared the growth rates of poison-ivy plants in normal conditions with plants receiving 1.5 times more carbon dioxide. They found that, each year, plants with the elevated carbon dioxide grew about 150 percent faster than the control plants and grew much faster than other woody plants subjected to the same conditions. The plants at elevated carbon-dioxide levels also survived better, so that the number of poison-ivy plants with high levels of carbon dioxide became about twice as big as those in control plots, over the course of the study.

In addition, the researchers found that the form of urushiol (the active compound in poison ivy that causes red, itchy rashes) in the plants with elevated carbon-dioxide levels was much more allergenic than that in the control plants.

"So much of the time, we hear about how rising levels of carbon dioxide are going to cause climate change, which certainly is something that should concern us all," says William Schlesinger, dean of the Nicholas School of the Environment and Earth Sciences and a co-author of the study, published in the Proceedings of the National Academy. "This study documents a direct effect of carbon dioxide on nature."

Getting a poison-ivy rash is "an experience that everybody remembers," he adds. "Even the biggest skeptic has got to recognize that this is something real."