https://en.wikipedia.org/wiki/Toxicodendron_radicans
Poison ivy is particularly sensitive to carbon dioxide levels, greatly benefiting from higher concentrations in the atmosphere. Higher carbon dioxide levels increase the rate of plant growth, and causes them to produce more unsaturated urushiol, which causes stronger reactions in humans.[12] Poison ivy’s growth and potency has already doubled since the 1960s, and it could double again once carbon dioxide levels reach 560 ppm.[10]