Climate change isn’t just warming the oceans and endangering polar bears.

It’s also breeding larger, more toxic poisonous plants. 

Plants basically need three things to grow: sunlight, water, and carbon dioxide. For millions of years, the supply of each of these ingredients remained relatively steady. Then came the Industrial Revolution, and people started burning fossil fuels to power their factories and vehicles, and heat and cool their homes. Today, there is more carbon dioxide in our atmosphere than at any other time in human history.

Researchers at the U.S. Department of Agriculture wanted to see how this atmospheric disturbance affected plant health. In the depths of Duke Forest, they planted giant rings of PVC pipes, which rose out of the forest floor all the way up to the top of the tree canopies. Through holes in the pipes, the scientists released either copious amounts of carbon dioxide or equivalent rations of ambient air. 

After six years, they found that poison ivy grew 149 percent faster in the presence of elevated levels of the greenhouse gas than it did under normal conditions. Not only did the supercharged plants grow larger, but they also produced more urushiol, the compound responsible for its characteristic itchy rash.

Follow-up studies have shown that the nasty weed’s growth and potency have doubled over the last fifty years.

That’s particularly bad news for the roughly 85% of the population who are allergic to poison ivy.

If you think you can avoid this summertime scourge by heeding the old adage “leave of three, let it be,” think again. Some have predicted that excess carbon dioxide will give rise to more mutant varieties with four or more leaves. 

Check our facts!


Written by Marla Vacek Broadfoot and illustrated by Bethann Garramon Merkle.

Marla Vacek Broadfoot is a geneticist-turned science writer. She currently serves as a contributing editor at American Scientist and an adjunct professor at the University of North Carolina at Chapel Hill. When she isn’t writing, Marla enjoys long walks in the woods with her family, often followed by the application of copious amounts of calamine lotion. Learn more about Marla here and follow her on Twitter @mvbroadfoot.

Bethann Garramon Merkle believes science and sustainability matter—her passion is communicating why. She is currently an illustrator and science communicator with the Wyoming Migration Initiative, where she works on public-facing projects and helps University of Wyoming faculty and grad students enhance their SciComm skills. Learn more about Bethann here or connect with her (@CommNatural) on social media.