Climate Central: The arrival of spring is kind of a good news/bad news story. The good news is that spring brings warmer weather and blossoms everywhere, as trees and flowers wake up from hibernation. But that’s also the bad news, at least for anyone who suffers from spring allergies. All of that flowering and leaf-opening means pollen will be filling the air and creating a yellow haze on cars — followed by sneezing, dripping, sinus-clogging misery for millions of Americans. Now here’s the worse news: rising carbon dioxide levels, mainly due to human-induced emissions, are increasing pollen production.

When scientists put plants in a growing chamber to test varying levels of CO2 on pollen production, the changes were significant — as the graphic above shows. Pollen production was more than twice as great when the chamber was set to 1999 CO2 levels (around 370 parts per million, or ppm) as it was when it was set to pre-industrial levels (about 280 ppm). And when the scientists cranked it up to 600 ppm, where things could be heading by the year 2060 (assuming we don’t curb CO2 emissions, that is), pollen production nearly doubled again.