Climate change fuels extended allergy seasons globally

Pollen plays a crucial role in our natural world. These tiny particles travel between plants, primarily from early spring to late summer, facilitating their reproduction. Some pollen is spread by insects, while others are carried by the wind. Unfortunately, this can cause allergies in sensitive individuals, and the effects may now intensify even more. Scientists believe that rising global temperatures are contributing to a longer pollen season, resulting in higher pollen levels in the air.

"We know that climate change is leading to greater amounts of pollen in the atmosphere. It's changing the seasonality of the pollen. It's changing the types of pollen that we're exposed to," says Paul Beggs, a scientist from Macquarie University in Sydney, in an interview with the BBC. This phenomenon is particularly observable in Europe, the United States, and Australia.

Researchers predict that pollen levels will be higher than the historical average in 39 U.S. states this season. This suggests that individuals with allergies may experience symptoms for a longer duration. "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," Lewis Ziska from Columbia University tells the BBC.

Scientists suggest that, without immediate reduction in greenhouse gas emissions, the situation will likely worsen. According to scientific studies published in "Nature" by Y. Zhang and A. Steiner, it's estimated that by 2100, pollen seasons will start up to 40 days earlier and end up to 15 days later than they do now – potentially resulting in an additional two months of symptoms for hay fever sufferers each year.

This issue is partly due to increasing levels of carbon dioxide (CO2) in the atmosphere from human activities. Many of the plants that cause significant problems for hay fever sufferers flourish on CO2.

The spread of invasive species to new regions also triggers allergic reactions in populations that haven't encountered them before. In some areas, such as the U.S. and Europe, one major culprit is ragweed (Ambrosia L), which belongs to the aster family—a widely spread group of flowering plants often considered weeds. There are various species of ragweed worldwide, but they can produce immense amounts of pollen. A single plant can emit a billion grains of pollen. Ragweed grows in gardens, farmlands, and even urban nooks.

Ziska, author of the 2022 book "Greenhouse Planet," conducted experiments with ragweed. "Every time we cranked up the carbon dioxide, the ragweed plants responded. They grew more. They produced more pollen," he told the BBC. He further noted that there is "some evidence that they were producing a more allergenic form of the pollen, one that could induce your immune system to respond even to a greater extent than had been in the past."

Climate change is significantly impacting human health, and without coordinated actions, the situation may deteriorate. "We now have research showing that it really affects human health," argues the scientist from Macquarie University in Sydney.