The new report, published in the journal Lancet Public Health, external, says climate change is extending the flowering season of some plants.
It looked at three trees common in Europe – birch, alder and olive – and found pollination started one to two weeks earlier between 2015 and 2024, compared with 1991 to 2000.
“We are seeing a prolonged season – an earlier onset of pollination in both the north and south [of Europe]”, says Professor Joacim Rocklov, from the University of Heidelberg, one of the authors of the paper.
He told the Today Programme on BBC Radio 4 that more research is needed to see if climate change could also be increasing the amount of pollen circulating and making hay fever symptoms more severe.
Early summer is often peak pollen season, when the number of grains of pollen in the air multiplies.
The warm weather seen in the UK over the last two years means conditions have been ideal for birch tree pollen – a major hay fever trigger.
Warm, dry days help spread pollen through the air, creating what’s been dubbed a “pollen bomb”.
Any extension of the pollen season could have an impact on millions of people across the UK.
“While for some their symptoms can be mild, for many their hay fever symptoms impacts their quality of life,” says Anne Biggs, deputy head of clinical services at Allergy UK.
“It can mean missed days at work, poor sleep and, for some teenagers and young people, active hay fever symptoms can mean they drop an academic grade in their exams.”
Pollen can also trigger asthma attacks and allergic reactions in people living with other respiratory conditions.
“If people are allergic to pollen, it can inflame their airways and cause terrifying breathing conditions, which can lead to life-threatening asthma attacks and COPD flare-ups,” says Dr Samantha Walker, director of research and innovation at Asthma and Lung UK.