Climate Matters•April 8, 2015

More CO2 = More Pollen

Set 4 - More CO2 = More Pollen
Set 4
Set 1 - More CO2 = More Pollen
Set 1

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.

  • One Caveat: most of the experiments so far have been done on ragweed, which sends out pollen in the fall, not the spring. The reason is that ragweed is easier to work with in the lab, and it’s well understood by scientists. But the experts in plant biology think that what holds for ragweed also holds for spring pollens.

When scientists put plants in a growing chamber to test varying levels of CO2 on pollen production, the changes were significant — as the graphic 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.

Climate change is adding to the allergy season in another way, too. Generally higher temperatures over the past few decades, mainly due to rising levels of heat-trapping carbon dioxide, have extended the frost-free season and made spring come earlier on average (although not this year in the East) — lengthening the pollen season. One study shows how the pollen season has been extended by as much as 10-21 days from 1995-2013 across northern Arkansas up into the Great Lakes. In fact, that study suggests higher latitude locations have extended their pollen season more than lower latitudes, where central Texas recorded a 1-day decrease in pollen season.