Handkerchiefs at the ready, Europe: the prevalence of hay fever is going to rise rapidly over the next 50 years because of climate change. Moreover, it’s likely to extend the hay fever season, while also making symptoms more severe.

A new study by researchers at the University of East Anglia and colleagues, found that for just one type of pollen—that of the ragweed Ambrosia artemisifolia—the number of people likely to suffer will more than double from 33 million to an estimated 77 million around 2050. The study claims to be the first to consider the big picture of how climate change affects a human pollen allergy, from a plant’s distribution to the health effects on populations.

Around 400 million people worldwide suffer from some form of hay fever, with current rates as high as 40% of the European population and 30% in the US.

Ragweed is native to North America—up to a quarter of the US population suffer ragweed allergy—but previous research found it to be spreading fast across Europe, particularly in the north, as it has become warmer since the 1960s. Ragweed is highly invasive and difficult to eradicate, benefiting from a long-lived seed and ability to evolve resistance to herbicides. Higher carbon dioxide levels, characteristic of global warming, are likely to spur it on further.

The plant is already rife in countries such as Hungary and Romania, but the new study predicts the biggest jumps in allergy sufferers will be in Germany, France and Poland where an increasingly warmer climate will boost plant growth and pollen production. A single ragweed plant already produces one billion grains of pollen a year.

Ragweed pollen normally peaks in the late summer, but the new models predict that warmer climates and delayed frosts will extend this into the autumn, possibly as late as mid-October in some regions. More pollen in the air—which could also be drier in some countries due to drought, altering the surface of the pollen and thus its potential to trigger allergies—could also make hay fever symptoms more severe, says Iain Lake, the University of East Anglia environmental scientist who led the study.

Although treatable with drugs, hay fever is more difficult to manage in older people, who may be suffering other conditions and be taking other medications at the same time. With the number of hay fever sufferers set to rise, and with the median age of the European population expected to rise from 38 to 52 by 2060, seasonal allergies is likely to become even more of a public health burden than it already is. Allergies are estimated to cost the European Union at least €55 billion ($62 billion) a year and hay fever is reported to be behind four million annual sick days worldwide.