Study Finds Climate Change is Impacting on Pollen Season

Dr Beverley Adams-Groom
Dr Beverley Adams-Groom

Research found a mixed picture of how climate change was affecting different types of pollen – with some starting earlier in the season and others becoming more severe.

It also highlighted how increasingly unusual weather coincided with erratic pollen seasons, and lower wind levels were affecting dispersal of pollen particles.

“Climate change is impacting on seasons positively and negatively,” said Dr Beverley Adams-Groom, senior pollen forecaster at the University of Worcester and lead author of the study. “It’s impacting some seasons so they’re getting worse, some seasons are starting earlier, some seasons are not getting worse. It’s a very mixed picture, but climate change is impacting on all these things. We can see that it is definitely having an effect.”

The University, which has been producing pollen forecasts for the country since 1995, led work with partners from five other institutions on the first study of how climate change is affecting pollen in the UK, which has been published in the Science of The Total Environment journal. Up until now, exploration of the issue had been restricted by not having a long enough period of time to observe any trends.

Researchers examined data from six pollen stations around the country between 1995 and 2020, focusing on key pollen types – grass, birch and oak. They looked at whether there had been significant changes in the patterns of these pollen seasons – such as onset, severity and duration. They analysed variations in weather to see if there were changes in the patterns that could be attributed to climate change.

Warmer weather is causing birch trees to produce more pollen and the study found the season is getting more severe across the country, particularly significant in the Midlands. This is bad news for the 20 to 30 per cent of hay fever sufferers allergic to birch pollen.

In contrast, the oak pollen seasons are starting earlier, but not getting more severe. Dr Adams-Groom puts this down to oak pollen production happening later in the summer (both birch and oak pollen are prevalent in early spring but produced the previous summer), in months where there have not been the same significant increases in temperatures.

The study revealed that the severity of grass pollen, which affects 95 per cent of hay fever sufferers, has overall remained steady, but there is a trend towards an earlier ‘first high day’. This is the first day the pollen levels reach the ‘high’ threshold. Dr Adams-Groom said an increase in temperature in key preceding months – January, May and June – was responsible and that this echoed findings in mainland Europe. She said a decrease in wind levels between May and August – again put down to climate change – could mask any increase in grass production. Moreover, woodland and urbanisation are reducing grassland in many areas.

Dr Adams-Groom highlighted how increasingly unusual weather is leading to a varying severity in seasons. She said a very dry spring in 2020, which led to grass not growing until rain arrived in June, led to a late start to the grass pollen season and not much pollen. However, in June last year, she said it was unusually cold in May and wet in early June, which also led to a delayed season. “Unusual weather patterns are sometimes setting the season back or lowering the amount of pollen produced in grasses as well, but are also lowering dispersal. We keep seeing these things going on and it’s the same with the birch pollen. Cold winds from the east are regularly stopping the birch trees from starting their season because it’s just too cold. This is climate change affected.”

Dr Adams-Groom said it was difficult to predict the long-term future as there are many factors at play and, if action was taken to limit the effects of climate change, this could have an impact in the long term. But, if the climate trajectory remains the same, over the next decade, she expects the trends identified by the study to continue. “We know there’s going to be more extreme weather events, that’s documented and that can impact on the seasons,” she said.

Read the full study at