Seasonal allergies are becoming more intense as higher temperatures stretch out pollen seasons, making episodes like thunderstorm asthma more common. Scientists warn that climate change is making allergies worse by increasing pollen levels and the severity of allergic reactions.
Thunderstorm Asthma: A Deadly Health Crisis
Many people enjoy watching storms as they develop, but inside these clouds, a biological storm is brewing. Thunderstorms can absorb large amounts of pollen and break it down into smaller particles through rain, lightning, and humidity. Once these pollen fragments fall back to the ground, people unknowingly breathe them in, which can trigger severe allergic reactions.
In Melbourne, Australia, on November 21, 2016, a deadly thunderstorm hit the city. Emergency services were overwhelmed as hospitals filled with patients struggling to breathe. Ambulances couldn’t reach everyone, and emergency rooms saw a tenfold increase in asthma-related admissions. Ten people died, including a young law student who collapsed on her lawn waiting for help.
Professor Paul Beggs, an environmental health expert from Macquarie University in Sydney, remembers the event. “It was unprecedented. Catastrophic. No one knew what was going on—doctors, nurses, or pharmacists,” he said. It wasn’t until later that experts identified thunderstorm asthma as the cause.
What Causes Thunderstorm Asthma?
Thunderstorm asthma happens when certain storms break apart pollen particles in the air. This releases proteins that can trigger allergic reactions in people—even those without asthma. Melbourne has experienced seven such events since 1984, but similar incidents have been reported in places like Birmingham, UK, and Atlanta, US. While rare, scientists believe climate change is making these events more common by lengthening pollen seasons and increasing storm severity.
Beggs believes that climate change played a role in the 2016 Melbourne event. “Climate change affects pollen quantities, types, and their seasonal timing,” he explains. His research shows that thunderstorms in a warmer climate are likely to become more intense, which could increase the frequency of thunderstorm asthma.
Rising Global Pollen Levels
As temperatures rise globally, pollen seasons are beginning earlier and lasting longer. Public health experts warn that people will experience allergy symptoms for longer periods each year. For example, ragweed, a common allergen in the US and Europe, produces huge amounts of pollen and is spreading to new regions as the climate warms. One ragweed plant can release up to a billion grains of pollen.
A study from 11 cities in North America found that pollen seasons in 10 of them grew significantly longer between 1995 and 2015. In some cities, the season stretched by more than three weeks. According to Dr. Lewis Ziska, a professor at Columbia University, climate shifts are extending the seasonal exposure to pollen. “Springs are starting earlier, and falls are delayed. Outdoor exposure to allergens is increasing,” he says.
If emissions continue unchecked, the situation could worsen. One study predicts that by the end of this century, pollen seasons could start 40 days earlier and last 15 days longer, adding an extra two months of symptoms.
How CO₂ Is Making Allergies Worse
Carbon dioxide (CO₂) is a significant factor in worsening allergy symptoms. Human-driven CO₂ emissions stimulate plant growth and increase pollen production. Experiments have shown that grass grown in environments with 800 ppm CO₂ produces 50% more pollen than those grown in 400 ppm CO₂, the current atmospheric level.
Oak trees in South Korea have also shown a dramatic increase in pollen production with higher CO₂ levels. At 720 ppm, trees released 13 times more pollen than at 400 ppm, and even at 560 ppm, the pollen count was three and a half times higher.
Dr. Ziska’s research into ragweed shows similar results. “Higher CO₂ levels make the plants grow faster, release more pollen, and in some cases, produce a more allergenic version,” he says.
Invasive Plants Are Spreading Allergens
The spread of invasive species, such as ragweed, is worsening allergy problems worldwide. While ragweed is native to North America, it now thrives in Europe, Australia, Asia, and South America. In Hungary, 60% of people are sensitive to ragweed pollen, while in Denmark, 20% of citizens are affected, and 15% in the Netherlands.
By 2050, ragweed pollen levels in Europe could increase fourfold. A third of this rise will be due to the plant spreading to new areas, and the rest will be driven by warmer temperatures and longer growing seasons.
Urban Planning and Pollen Management Can Help
There are ways to manage the growing pollen problem. Reducing carbon emissions could help slow down climate change and, in turn, reduce the intensity of allergy seasons. Cities have also made efforts to control ragweed. For example, Berlin has a team that removes ragweed, and Switzerland has banned the sale and import of the plant.
Urban planning can also play a role in reducing allergens. Experts suggest that choosing the right plants for cities is crucial. Some plants, especially male trees that produce pollen, should be avoided to lower allergy risks. Though the impact of “botanical sexism” in urban areas is small, it can still be important.
Real-time pollen monitoring could also help. “We need to know what we’re breathing,” says Professor Beggs. While temperature and rainfall data are commonly available, real-time airborne allergen data is not as accessible. Tracking allergens directly, not just pollen grains, would provide more accurate health risk information.
Taking Action Before It’s Too Late
Scientists agree that without action, climate change will continue to worsen allergies and trigger more severe health events like thunderstorm asthma. “The health impact is real. And it’s just beginning,” says Professor Beggs. To protect public health, governments and cities need to take immediate steps to monitor pollen levels and reduce emissions to slow the effects of climate change on allergies. If not, millions of people will continue to suffer from more intense allergy seasons and potentially deadly asthma events.