If you've ever thought what humans are doing to the planet is on the nose, you're right in a way you may not have expected. Pollen seasons are getting longer, and warmer temperatures are to blame. So if every spring you can’t stop sneezing and your eyes hurt, you can not only blame your Neanderthal ancestry or the lack of a protective cell type, but the burning of fossil fuels. The bad news is, the future looks worse.
Many allergy sufferers have a sense that things are getting worse, but the blame could lie anywhere from a changing mix of plants in their local vicinity to susceptibility increasing with age. However, Dr William Anderegg of the University of Utah thought there might be something more widespread at play. He investigated changes in pollen abundance over the last three decades, and has pinned the blame firmly on global warming.
"A number of smaller-scale studies - usually in greenhouse settings on small plants - had indicated strong links between temperature and pollen," Anderegg noted in a statement. "This study reveals that connection at continental scales.”
Fortunately for our knowledge of the topic, the National Allergy Bureau maintains pollen count stations across the United States, which also track the amount of mold in the air. By combining these with some extra stations in Canada, Anderegg constructed a record of North American allergens between 1990 and 2018 and compared it with climate observations over the same period.
On average, pollen increased by 21 percent over the period of time Anderegg reports on in Proceedings of the National Academy of Sciences. The connection to temperatures is emphasized by pollen season now starting 20 days earlier in spring, partially compensated by finishing ten days earlier.
The trend is much stronger in a band from Texas up through the Midwest.
Anderegg and co-authors tested whether climate change really is behind the increased pollen abundance, or just coincidentally operating on a similar timeline. They found that pollen has increased the most where temperatures are rising fastest, accounting for around half the extra high pollen days. On the other hand, only a small portion of the extra annual pollen abundance is driven by rising temperatures.
If you think that means the release of carbon into the atmosphere is a minor contributor, however, you may want to think again. The studies in actual greenhouses Anderegg referred to show pollen production is also related to ambient carbon dioxide levels. In addition to the indirect temperature effects, changes to the atmosphere are probably increasing pollen production directly, although this can't be checked statistically using Anderegg's data.
Besides their effect on the sufferer's quality of life, allergies can affect respiratory health and increase the spread of infections, both by increasing virus transmission and making outbreaks less likely to be noticed early on.
"Climate change isn't something far away and in the future. It's already here in every spring breath we take and increasing human misery," Anderegg said.