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Spring brings fresh flowers and warmer weather, but these seasonal changes also herald the beginning of the allergy season for about 40 million Americans. As pollen proliferates, so are sneezing, itching and nosebleeds due to hay fever.
If you feel that your allergies are getting worse with each sunrise, this may well be the case. And there is one major culprit to blame: climate change.
Read more: Allergies really worsen – it's not that you're
According to the Union of Concerned Scientists, carbon dioxide (one of the greenhouse gases that humans emit that retains heat on the planet) increases the rate of plant growth. This, in turn, increases the amount and potency of the pollen.
In addition, rising temperatures – caused by increasing levels of carbon dioxide – lengthen the growing season of pollen-producing plants. This, of course, extends the allergy season. Higher temperatures can also cause individual plants to produce more pollen and expand the geographical range of these plants.
Why a warming planet leads to longer and more intense seasons of allergies
The increase in carbon emissions results in the increase of the average surface temperature of our planet. Last year was the fourth hottest year ever recorded and the hottest year ever recorded for the oceans. (Like most things, the water expands when it is heated, which is why the sea level rises.)
According to the American Foundation for Asthma and Allergy (AAFA), these higher temperatures prolonged the pollen season in the United States by 27 days between 1995 and 2011. Isabella Annesi-Maesano, director of research at the US French Institute of Health and Medical Research, said Business Insider that this warming is why we are also witnessing an "earlier pollen season".
A recent study published in The Lancet analyzed pollen season length and pollen quantity per plant in 17 sites in the northern hemisphere. According to data collected over 26 years, 70% of the localities recorded an increase in the total amount of pollen circulating per growing season. In 65% of cases, the pollen season has lengthened due to a "continuous increase in extreme temperatures," reported the authors.
Lewis Ziska, the lead author of this study, works as a weed ecologist with the US Department of Agriculture. He spoke to the Union of Concerned Scientists about another climate-related allergy problem: plants use carbon dioxide to produce food via photosynthesis, but an extra amount of dioxide Carbon in the air results in faster growth of pollen-generating and allergic weeds than "useful plants" like rice and wheat.
"Ragweed, in particular, grew faster, bloomed earlier and produced significantly larger pollen," he said.
Ragweed is the main trigger of autumn hay fever, according to the AFOA. Warmer temperatures lead to longer growing seasons for ragweed, allowing the plant to continue producing more pollen later in the fall.
If carbon dioxide emissions continue unchecked, ragweed pollen production could increase by 60% to 100% over the next 65 years. Ragweed pollen could also become more allergenic as carbon dioxide levels increase, according to AFOA.
Allergies could continue to worsen
According to Annesi-Maesano, floods due to sea level rise can also cause another type of allergy.
"The floods are the cause of the proliferation of molds," she said; mold can cause irritation of the respiratory tract and is a common trigger of asthma and allergies.
Children are more susceptible to all these allergens because their organs and immune systems are still in training and because they are more exposed to climate-related contaminants. In particular, children in low- and middle-income countries are disproportionately affected by the consequences of global warming, said Annesi-Maesano.
"Age matters in climate change, with children and older people being more affected by the effects of climate change than the rest of the population," she added.
According to Annesi-Maesano, "it seems likely" that allergies will continue to worsen if carbon emissions continue to increase.
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