Spring is a season of rebirth. As temperatures warm, plants awaken from winter dormancy, generate pollen, and produce beautiful blooms. For allergy sufferers, however, the season can be a double-edged sword. With climate change extending the growing season, the outlook for people with seasonal allergies is less than rosy.

Across the US, the growing season – the period between the last and first freezes of the year – has lengthened by an average of two weeks since the 1970s, according to Climate Central. That means pollen allergies are staring earlier in the spring and lasting longer into the autumn. Tree pollen comes out in the spring, grass pollen strikes in the summer, and weed pollen is prevalent in the fall.

If global warming continues unchecked, studies show the growing season, and therefore the allergy season, expanding even further.

These changes to the growing season, like other climate change impacts, vary from region to region. The largest increase has been noted in the western states, according to the National Climate Assessment. Here in NYC, the growing season has increased an average of 21 days between 1970 and 2018.

Rising temperatures, however, are not the only factor for worsening allergy conditions. The carbon dioxide (CO2) in the air that causes the atmosphere to warm also plays a more direct role. When plants, particularly ragweed, are exposed to higher levels of CO2, they produce more pollen. Therefore, as concentrations of atmospheric CO2 continue to increase, pollen production will intensify.