Climate Change Could Make Poison Ivy Grow 150% Faster

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%. 

What's more, higher CO2 levels make urushiol, the allergen in these plants, stronger. Increased CO2 levels in coming decades will likely lead to bigger, quicker-growing poison ivy plants. And those poison ivy plants will have a bigger impact on us, causing even worse skin reactions when we come into contact with them. 

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. 

The preliminary results of this study also suggest that plants of poison ivy in warmer soil will be larger too. Thus far it does not look as though urushiol levels are increased, so that is one small comfort.

However, it is clear that with the supercharging effects of both increased CO2 and warming soils, poison ivy will become an increasingly troublesome plant as our climate crisis continues. And, unfortunately, our rising populations and increased impact on our environments do not just contribute to the climate crisis, they also benefit poison ivy in other ways.

Where people go, poison ivy follows

Another concern, especially with the super-charging of poison ivy by climate change, is that humans are making ideal environments for this plant to thrive. Where people make inroads into nature—for hiking trails, campsites, and picnic spots, for example—they alter the habitat and make ideal conditions for poison ivy to thrive. 

Poison ivy likes areas of human disturbance. It thrives in areas where there are fewer other plants and plenty of sunlight. So where people break up forests, poison ivy can more easily take hold. They will not grow as much or broadly in shaded spots in undisturbed forests. 

The impacts of climate change on plants are many and varied—and in many instances, humankind suffers from the changes that occur. Of course, many plants are endangered by the droughts and flooding which are becoming increasingly prevalent as our planet warms, and even the slightest environmental change can be devastating to the delicate ecosystems upon which we all depend. 

While plants like poison ivy can thrive, other plants on which we depend will suffer. Scientists have learned, for example, that climate change is making crops less nutritious. When food crops like wheat, corn, rice, and soy are exposed to CO2 at levels predicted for 2050, the plants lose as much as 10% of their zinc, 5% of their iron, and 8% of their protein content.

This is just one more reminder of the serious impacts of our climate crisis—and the urgent need for change.