By Elizabeth Waddington

In Eastern North America and parts of Asia, poison ivy (Toxicodendron radicans) is a common irritant of the landscape. This noxious weed is well known for causing an itchy, irritating, and sometimes painful rash on contact. This highly variable plant can be a small plant, a shrub, or a climbing vine, though is commonly characterized by clusters of leaves, each containing three leaflets. This has lead to the common expression “leaves of three, let it be.”

Contact dermatitis is caused by urushiol, which, for some people, has no effect at all. However, 70-85% of the population will have an allergic reaction to some degree. And even those who have no reaction or only a mild reaction on the first contact should note that most people have a greater reaction with repeated or more concentrated exposure.

There is also some very bad news for those who live in areas where this plant is widespread: climate change is supercharging these plants, making them even bigger, stronger, and more potent.

Spiking carbon dioxide levels means stronger poison ivy

A 2006 Duke University study found poison ivy grows to double its normal size when exposed to higher levels of carbon dioxide—levels on a par with those expected by around 2050. The leaves on some plants grew by as much as 60%.

Rising soil temperatures may also benefit poison ivy

Unfortunately, it seems there is another climate-related factor that makes poison ivy more of a threat. Early-stage findings from research at Harvard University’s Harvard Forest, in Petersham, Massachusetts, suggest that if, as the worst-case climate models show, climate change causes soils to warm by 9 degrees Fahrenheit (5 degrees Celsius), poison ivy will grow 149% faster on average compared to ambient soil temperatures.

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