From Climate Central:
Nearly 20 million Americans suffer from pollen allergies. Analysis of local temperature data by Climate Central and recent scientific research show that climate change is prolonging their season of suffering.
Global warming is extending the freeze-free season, giving plants more time to grow, flower, and produce pollen. And as atmospheric carbon dioxide (CO2) levels rise, laboratory experiments suggest, some plants that produce allergenic pollen produce even more of it.
These trends will worsen as humanity dumps more carbon into the atmosphere. Like global warming’s effects on heat waves and vector-borne diseases, climate change’s consequences for pollen allergies reveal how greenhouse gas emissions are already damaging Americans’ health…
More CO2 = More Pollen
By trapping more heat in the atmosphere, humanity’s carbon emissions have made the growing season longer. But carbon emissions also directly spur pollen production in some allergenic plants, independent of changes in temperature.
Take ragweeds, which are the third-most common allergen in the United States. Roughly one in four Americans are sensitive to their pollen.
Scientists have conducted laboratory experiments to determine how ragweed responds to various concentrations of CO2. One study showed that, as CO2 concentrations rise from 280 to 370 parts per million—which is what actually occurred in the global atmosphere between about 1900 and 2000—ragweed pollen production more than doubles. Under a CO2 concentration of 600 parts per million, ragweed pollen production doubles again. Today, atmospheric CO2 stands around 410 parts per million; if emissions grow unchecked, we could reach 600 parts per million in about 40 years. Similar patterns hold for timothy grass pollen, another common allergenic plant that sends out pollen early in the summer.