How climate change is supercharging allergies
By BBC, April 21, 2026Seasonal allergy sufferers are being hit with more pollen over a longer season due to rising temperatures, but global warming is also triggering alarming extreme allergy events, say experts.
People could see the thunderstorm, but they couldn’t see what was going on inside it. Trillions of pollen particles, sucked up into the clouds as the storm formed, were now being splintered by rain, lightning and humidity into ever-smaller fragments – then cast back down to Earth for people to breathe them in.
It was around 18:00 on 21 November 2016 when the air in Melbourne, Australia, turned deadly. Emergency service phone lines lit up, people struggling to breathe began flooding into hospitals, and there was so much demand for ambulances that the vehicles were unable to reach patients stuck at home. Emergency rooms saw eight times as many people turning up with breathing problems as they would normally expect. Nearly 10 times as many people with asthma were admitted to hospital.
In total, 10 people died, including a 20-year-old law student who passed away on her lawn, waiting for an ambulance while her family tried to resuscitate her. One survivor described how he had been breathing normally and then, within 30 minutes, found himself gasping for air. “It was insane,” he told reporters from his hospital bed.
Paul Beggs, an environmental health scientist and professor at Macquarie University in Sydney, Australia, remembers the incident well. “It was an absolutely massive event. Unprecedented. Catastrophic,” he says. “The people in Melbourne, the doctors and the nurses and the people in pharmacies – they all didn’t know what was happening.”
It soon became clear that this was a massive case of “thunderstorm asthma”, which occurs when certain types of storms break up pollen particles in the air, releasing proteins and showering them on unsuspecting people below. The widely dispersed proteins can trigger allergic reactions in some people – even among those who weren’t previously asthmatic.
Thunderstorm asthma events like the one that hit Melbourne are one extreme example of how pollen from plants and the allergies it causes are being dramatically altered by climate change. As temperatures rise, many regions – especially the US, Europe and Australia – are seeing seasonal allergies affect an increasing proportion of people, over a longer season and with worse symptoms, say scientists.
This year, in the US, pollen levels are predicted to be higher than the historical average across 39 states this season. And that is only likely to get worse in the years to come, experts warn.
Pollen itself is an essential and ever-present part of our world. These microscopic particles pass between plants, enabling them to reproduce. While some plants spread their pollen with the help of insects, others rely on the wind, sending huge volumes of this powdery substance airborne. Many trees, grasses and weed species rely upon wind dispersal for their pollen. It is these that are especially likely to cause seasonal allergies, or hay fever.
This occurs when your immune system mistakenly identifies the pollen as a harmful substance, triggering a response normally reserved for pathogenic bacteria or viruses. Common symptoms can include a runny nose, itchy eyes and sneezing. In some cases, seasonal allergies can trigger breathing difficulties when inflammation in the airways leads to swelling, making it hard to get enough air into the lungs.
While Melbourne has been the unlucky epicentre of thunderstorm asthma, with seven thunderstorm asthma major events recorded since 1984, similar incidents have occurred around the world, from Birmingham in the UK to Atlanta in the US. Although these are still rare events, climate change may be increasing the likelihood of thunderstorm asthma incidents, in part because it is extending pollen seasons, but also because it is increasing the frequency of extreme weather events, including storms.
While it isn’t possible to determine exactly how much climate change influenced the 2016 thunderstorm asthma incident in Melbourne, Beggs is “reasonably certain” it had some impact.
“We know that climate change is leading to greater amounts of pollen in the atmosphere,” he says. “It’s changing the seasonality of the pollen. It’s changing the types of pollen that we’re exposed to.” Beggs, who has researched thunderstorm asthma extensively, published a paper in 2024 that examined the links between this phenomenon and climate change.
Thankfully, major thunderstorm asthma events remain rare. But climate change is increasing people’s risk of pollen exposure in other ways, too.
For one thing, rising temperatures mean that pollen seasons – when plants emit pollen, typically during spring and summer – are starting earlier and lasting longer, says Elaine Fuertes, a public health scientist who focuses on the environment and allergic disease at the National Heart and Lung Institute, Imperial College, UK. “You’re going to get people who experience symptoms earlier in the year, for a longer period of time,” she says.
In parts of the world, including the US and Europe, one of the key culprits is ragweed – a widespread group of flowering plants that many people consider to be weeds. There are various species of ragweed around the world but they can produce mind-bending amounts of pollen. A single plant is capable of emitting one billion pollen grains, for example. Ragweed grows in gardens and farmland but also in nooks and crannies in urban environments.
Allergies to ragweed pollen already affect some 50 million people in the US alone. A study analysing data from 11 locations in North America between 1995 to 2015 found that 10 of those locations experienced longer ragweed pollen seasons – sometimes much longer. During that 20-year period, the season lengthened by 25 days in Winnipeg, Manitoba, 21 days in Fargo, North Dakota and 18 days in Minneapolis, Minnesota.
“The winter warms, the springs are starting earlier, and the falls are being delayed, and so the time that you spend outdoors in contact with allergic pollen is definitely going up,” says Lewis Ziska, associate professor of environmental health science at Columbia University, in New York, US, and one of the scientists who researched the ragweed pollen season.
These changes get more drastic in northern parts of North America, Europe and Asia, Ziska says. But also in Australia and the southern parts of South America and Africa.
Without immediate cuts to greenhouse gas emissions, the effect is likely to only get worse. One 2022 study, for example, estimated that, by the end of the century, pollen seasons will begin up to 40 days earlier and end up to 15 days later than they do now – potentially meaning an additional two months of symptoms for hay fever sufferers per year.
It isn’t just that people are being exposed to allergens for longer. It is also that the amount of allergens in the air are increasing in many parts of the world. In the 2000s, the pollen season in the continental US started three days earlier than it did during the 1990s, but crucially, the amount of pollen in the air was also 46% higher.
This is partly because carbon dioxide (CO2) levels in the atmosphere are rising, due to emissions from human activities. And many of the most bothersome plants for hay fever sufferers thrive on CO2.
When researchers grew a certain type of grass under different CO2 levels, for example, they found that plants grown in an atmosphere containing CO2 at 800 parts per million (ppm) had flowers that produced about 50% more pollen than plants grown in air containing 400ppm. The latter mimics current levels of CO2 in Earth’s atmosphere.
Similarly, other scientists have also experimented with growing different types of oak tree, the pollen from which often causes hay fever in countries such as South Korea. Under a 720ppm CO2 scenario, they found that each oak tree had an average pollen count 13 times what the trees had under a 400ppm scenario. Even at 560ppm, pollen production was 3.5 times higher than current levels.