If you have sneezed your way through the last few days, you are not alone. About a quarter of the UK population are thought to suffer from hay fever, with numbers continuing to grow. And the latest research suggests that the climate crisis is going to make the hay fever season a whole lot longer and more intense, with up to three times as much pollen wafting around by the end of the century. Hold on to your antihistamines.
For people with lung conditions such as asthma or chronic obstructive pulmonary disease, pollen bursts are a serious risk that can be deadly in the most extreme cases. In November 2016, a pollen outbreak caused by a thunderstorm fragmenting pollen into smaller pieces in Melbourne, Australia, overwhelmed the emergency services and resulted in at least nine deaths.
Already we are feeling the effects of a longer growing season, with plants in the UK having a whole extra month of productivity compared with 30 years ago. Birch, alder and oak trees are usually first to bloom, spraying their pollen – the dust-like grains that hay fever sufferers are allergic to – as early as February, in some years. The deciduous trees are followed by grass pollen in late spring and summer, and finally weed pollen (such as ragweed and dock) is picked up by the breeze in later summer and early autumn.
The impact of the longer growing season has been felt most in the north of Britain. One recent study showed that the onset of the oak pollen season in Invergowrie, Scotland, now starts some 20 days earlier compared with the 1990s. At the same time, our changing climate is altering the distribution of allergenic plants, with some particularly potent species invading new areas.
But the main driver of growing pollen is increasing levels of carbon dioxide. While higher temperatures extend the growing season, carbon dioxide fuels photosynthesis, enabling plants to grow larger and produce more pollen. Researchers from the University of Michigan have been monitoring pollen production from 15 different types of plant across the US. Using a climate model, they projected how the pollen production is likely to change between now and 2100. Under a high carbon-emissions scenario, their modelling suggests that this boost to plant growth, plus greater overlap in the pollination season for trees, grasses and weeds, will result in a whopping 200% increase in pollen levels across the US by 2100.
Evidence is also emerging that air pollution is enhancing the allergenicity of pollen particles. Some pollutants such as nitrogen dioxides (predominantly from car exhaust pipes) are thought to bind themselves to pollen particles and exacerbate allergic disorders. Others damage the surface of the pollen grain, releasing lots of mini-fragments of pollen that can penetrate deeper into the lungs.
So what can we do to tackle the misery that hay fever brings? In urban areas, reducing levels of air pollution is an obvious quick fix: car-free zones, low-traffic neighbourhoods and clean air zones will all help air pollution to fall. Meanwhile, choosing to plant low-allergenic trees and grasses is important too, as is designing green spaces carefully, to avoid tree canopies acting as a lid for air pollutants.
Avoiding the pollen boost from rising levels of carbon dioxide is trickier though. Clearly we need to make every effort to reduce our carbon emissions to avoid the worst impacts of the climate emergency, but even if we were to eliminate our carbon emissions tomorrow, the cumulative effect from our historical emissions has locked in an increase in carbon dioxide until about 2060 at least. So we can’t stop the pollen explosion that additional carbon dioxide will bring, but we can forecast it.
In the same way that weather forecasts help people to prepare for and avoid dangerous weather, researchers are confident that we can increase the accuracy of our pollen forecasts, enabling people to take preventive action. Scientists at the University of Worcester and their colleagues have been using weather and pollen measurements from across north-west Europe to give advance warning of how severe a pollen season is going to be, based on the weather conditions in the preceding months (which affect the vigour with which a plant grows). Meanwhile, scientists from the University of Michigan have been combining pollen measurements, weather forecasts and satellite data to pinpoint where and when pollen starts to be sprayed, in order to develop targeted and precise pollen forecasts.
These kind of pollen early warning systems will be a crucial tool for the future, alerting sufferers to dose up on antihistamines, wear a mask outdoors and stay indoors during peak-pollen parts of the day. Like flooding, heatwaves and other extreme weather, more intense and widespread hay fever is yet another consequence of the climate crisis that we are just going to have to learn to live with.
Kate Ravilious is a freelance science journalist based in York, UK; she writes on Earth, climate and weather-related issues
