Hay fever sufferers may have noticed their allergies getting worse. What role is climate change playing?
As if climate change doesn’t already come with enough challenges, it appears there’s another we can add to the list: bringing more agony to hay fever sufferers.
Earlier this year the Met Office warned that hay fever could get worse due to climate change. And it’s not just a hypothetical future problem: in a recent paper researchers dug into pollen trends over the last 26 years across the UK, focussing on grass, birch, and oak pollen, to investigate how changing weather patterns are already affecting hay fever season.
While the work showed that climate change is certainly having an effect, the exact changes depend on which kind of pollen you’re affected by. The season for birch pollen, the second most important type when it comes to hay fever after grass pollen, is increasing in severity – meaning the total amount of pollen seen during the season is higher.
Oak pollen season is also starting earlier and lasting longer. But some good news is that grass pollen, while the first day with high pollen levels seems to be getting earlier, the season doesn’t appear to be getting worse.
The data in the study only goes as far as 2020, but Dr Beverly Adams-Groom, lead author of the paper and senior palynologist and pollen forecaster at the University of Worcester, says those trends appear to be continuing.
“The birch pollen season this year and in 2021 were amongst the very worst that we’ve ever seen,” she says.
Why does hayfever season happen?
Pollen is a fine powder made by plants as part of their reproductive cycle, and hay fever is an allergic reaction to proteins found on the pollen when it gets into our eyes, nose, and throat.
In the UK there are three main hay fever seasons caused, respectively, by tree pollen which starts in March until mid-May, grass pollen which typically lasts from mid-May to July, and weed pollen from the end of June until September.
And then when it comes to climate change, in theory, higher levels of carbon dioxide in the atmosphere and warmer temperatures should stimulate plant growth, meaning plants can grow faster, flower earlier, and make more pollen.
A European team of researchers has shown that grass pollen season in countries including the UK could get much worse if we don’t significantly rein in the amount of carbon dioxide we’re releasing into the atmosphere, predicting that that the amount of grass pollen could increase by up to 60 per cent if carbon dioxide levels were to double.
But in reality, the effects are a bit more complicated because of changing weather patterns caused by climate change.
How is climate change impacting pollen production?
In the UK we are already seeing warmer, wetter winters; hotter, drier summers; and more frequent and intense weather extremes. Both the weather conditions when a plant is producing pollen, and the conditions when it releases that pollen, plays a part in determining how much reaches the eyes and noses of hay fever sufferers in any given year.
Higher temperatures and more sunshine hours earlier in the year are driving the increase in oak pollen in recent years. Rising temperatures are also what is making birch pollen season worse.
“Birch pollen production occurs usually in June of the previous summer, and it’s released in April,” says Adams-Groom.
If we have warm weather in the summer, then tree pollen season the following year is likely to be more severe – but exactly how bad it ends up being depends on the weather that next year, too.
“We need to have good weather in-season for the pollen to actually be dispersed,” says Adams-Groom. “If it’s raining all the time, if it’s cold, then the pollen grains will remain within the flowers.”
Grasses produce their pollen closer to when they release it. A sustained number of warm, dry days during grass pollen season – such as when we experienced the hottest June on record – can result in a lot of high pollen days in a row, but then lead to grasses quickly depleting themselves and a season that ends earlier than usual.
But drier weather earlier in spring can mean grasses don’t produce as much pollen as usual.
To complicate things further, it’s possible that the pollen count doesn’t give us a full picture of how bad someone’s hay fever symptoms are likely to be on any given day – there could be another factor behind anecdotal reports that hay fever seasons are getting tougher, says Adams-Groom.
Other emerging research shows that factors including carbon dioxide and air pollution can increase the potency of pollen grains, meaning that even if the amount of pollen in the air is not going up – and the season overall isn’t getting more severe – each pollen grain could be carrying more of the allergenic protein that causes hay fever symptoms.
“We can’t be sure exactly what’s going on,” says Adams-Groom. “But we have to assume that, possibly, despite the fact that the amount of pollen itself isn’t increasing in the atmosphere, that the potency might be – there might be more what’s called free allergen in the atmosphere.”
All of this adds up to the potential for hay fever seasons to get worse with climate change. But, much like trying to predict the weather, the devil will be in the details – and we’ll have to wait for each season to arrive before we truly know how bad (or not-so-bad) it’s going to be.
About our expert, Dr Beverley Adams-Groom
Beverley is a leading expert in pollen forecasting and provides the UK and Ireland with forecasts for all the main airborne allergens, working in association with the UK Met Office.
Her work has been published in the journals Current Biology and the European Journal of Allergy and Clinical Immunology.
Read more about allergies:
- What does a hay fever tablet do?
- Is local honey a cure for hay fever?
- Do allergies, such as hay fever, follow cycles?