Warming set to raise the pollen count

Pollen from common ragweed is a major trigger of seasonal allergies.
Image: Frank Mayfield via Flickr

Hay fever and asthma are likely to become a much greater health issue in Europe as warming stimulates plants producing allergenic pollen.

LONDON, 4 September, 2016 – Allergic diseases already cause misery for hundreds of millions of people, with serious implications for public health budgets in both developed and developing countries.

But new research suggests their prevalence will reach epidemic proportions over the coming decades – because, in a changing climate, allergenic pollen-producing plants will thrive.

A study funded by the European Union focuses on common ragweed (Ambrosia artemisiifolia), a highly-invasive plant originally from North America that grows in fields, roadsides and gardens. It is one of the main triggers of seasonal allergies – close behind dust mites and rye grass – and is now spreading fast in Europe and Australia.

Once established, ragweed is quick to colonise, especially where ground has been newly disturbed. It is particularly harmful for public health because each plant can produce as many as a billion pollen grains per season, which can travel hundreds of miles on the wind.

Allergy rates

Researchers from the University of East Anglia, UK, and several European institutes have investigated the likely impact of climate change on ragweed distribution and resulting allergy rates for Europe’s population.

They created maps of estimated ragweed pollen counts over the pollen season and combined them with data on where people live and levels of allergy in the population.

Their findings suggest the number of Europeans sensitised to ragweed pollen will double in the next 35 years from 33 million to 77 million. Those sensitised will be at high risk of developing allergic rhinitis (hay fever) and asthma, as well as other allergic conditions such as conjunctivitis and eczema.

“Ragweed pollen allergy will become a major health problem across Europe, expanding into areas
where it is currently uncommon”

The study predicts that a warming climate will allow the plant to expand its range northward from hot spots in the Balkans, Austria and northern Italy into Germany, France and Poland. By 2041-2060, it is expected to spread across the whole of Europe, apart from Scandinavia, the Baltic states and most of Spain and Ireland.

To make matters worse, a longer summer growing season and increased atmospheric carbon dioxide concentrations will extend the pollen season and allow individual plants to grow more vigorously, producing still more pollen.

The most noticeable change will be felt in countries such as France, Germany and Poland, where at present few people have become sensitised to ragweed pollen. The UK and the Netherlands may also be affected.

Lead author Iain Lake, reader in the University of East Anglia’s School of Environmental Sciences, says: “Ragweed pollen allergy will become a major health problem across Europe, expanding into areas where it is currently uncommon.

“Control of ragweed is essential for public health, and as an adaptation strategy in response to climate change.”

But it may be possible to control it effectively with land management that minimises soil disturbance, combined with stricter controls on transport of crops and other goods that may be contaminated with ragweed seeds.

Extremely resilient

This may not be straightforward because, apart from its exceptional reproduction rates, ragweed is also extremely resilient.

Studies have shown it can become resistant to herbicide. It quickly re-sprouts after cutting, and its dormant seeds can survive a long time in the ground.The allergenic impacts of climate change will not be limited to ragweed. Previous research suggested that warmer conditions tend to boost the production and release of a wide range of allergenic pollens and fungal spores.

“Generally, when it is warmer plants tend to do better – they produce more pollen and so on,” Dr Lake says. – Climate News Network

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