Climate change may see pollen season in the US begin earlier and end later by the end of the century – and those with hay fever may experience worse symptoms as pollen emissions could rise by as much as 250 per cent
15 March 2022
Pollen season may start up to 40 days earlier by the end of the century in the US if temperatures continue to rise as predicted. It could also last longer and be more intense.
Allergies induced by pollen such as hay fever affect up to 30 per cent of the world’s population. “We have already seen a change in the pollen count in the last few decades,” says Yingxiao Zhang at the University of Michigan. “The increase in pollen in the atmosphere starts earlier now and the main driver of that is temperature change.”
Zhang and her colleagues wanted to find out what pollen season may look like at the end of the century. The team combined climate models with data taken between 1995 and 2014 from sites across the US for levels of 13 of the most common types of pollen in order to predict levels between 1981 and 2100.
The researchers found that plants would start releasing pollen up to 40 days earlier if temperatures in the US rose between 4 and 6°C. For example, pollen released by alder trees (Alnus) may peak in February rather than March.
They also found that plants that pollinate later in the year such as grasses may do so up to 19 days later – lengthening pollen season and increasing annual pollen emissions across the US by between 16 and 40 per cent.
Factors other than temperature would have an effect too: increasing carbon dioxide levels could have the biggest impact on pollen emissions. Based on findings from previous lab studies, the researchers found that the predicted atmospheric CO2 rise this century may increase pollen emissions across the US by up to 250 per cent.
The researchers say that CO2 may have such a big effect because it has such a crucial role in photosynthesis. “More carbon dioxide may mean plants grow bigger and stronger and this would impact the release of pollen,” says Zhang.
“But there’s a huge amount of uncertainty in that result as we don’t have a lot of data on the effects of carbon dioxide on pollen,” she says.
Anyone with hay fever will fare far worse if these predictions come true, Zhang says, as pollen season will be longer and daily pollen counts will also be higher. But the study didn’t take into account other effects, such as a likely rise in the number of droughts and floods due to climate change. These will also influence plant life and therefore pollen count.
“For nearly all children with asthma, more pollen means greater chances they’ll have an asthma attack,” says Aaron Bernstein at Harvard University. “So we can hope that this study got it wrong, but odds are it didn’t.”
“We already know we have so much to gain for the health of our children, especially children growing up in poverty, when we act on climate change, and I hope that this study gives still greater incentive for the parents of the 6 million children with asthma in the US to call for policies that will prevent needless suffering for our nation’s children.”
Journal reference: Nature Communications, DOI: 10.1038/s41467-022-28764-0
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