People suffering from hay fever may have noticed that their seasonal allergies are getting worse. While climate change may not feel like an immediate crisis at all times, it is already having a measurable effect. Add another consequence of global warming to the list: a link to seasonal allergies.
The Impact of Climate Change on Hay Fever
Earlier this year, meteorologists warned that hay fever could worsen because of climate change. This is not just a hypothetical problem for the future.
In a recent study, researchers examined pollen trends over the past 26 years in the United Kingdom. They focused on grass, birch, and oak pollen to investigate how changing weather patterns are already affecting the hay fever season.
While the study confirmed that climate change does have an impact, the exact effects depend on which pollen species trigger an individual’s allergies. The birch pollen season, which is the second-most significant contributor to seasonal allergies after grass pollen, is becoming more severe. That means the total amount of birch pollen observed during the season is rising significantly.
The oak pollen season is also starting earlier and lasting longer. The good news is that grass pollen—the biggest contributor to seasonal allergies—does not appear to be increasing compared with past years, even though it is arriving earlier.
The data from the study cover only 2020. But, as lead author Beverly Adams-Groom says, these trends are persistent. She points out that the birch pollen season in 2021 was one of the worst we have ever seen.
What Causes Seasonal Allergies?
Pollen is a fine powder produced by plants as part of their reproductive cycle. Hay fever is an allergic reaction to the proteins in pollen when they enter the eyes, nose, and throat.
There are three main hay fever seasons. The first, tied to tree pollen, begins in March and lasts until mid-May. The second, linked to grass pollen, runs from mid-May to July. The third, associated with weeds, lasts from late June to September.
When it comes to climate change, higher levels of carbon dioxide in the atmosphere and warmer temperatures should theoretically stimulate plant growth. That can make plants grow faster, bloom earlier, and produce more pollen.
A European research group has shown that the grass pollen season in some countries could worsen if major steps are not taken to curb carbon emissions. They predict that if carbon dioxide levels double, pollen production could increase by as much as 60 percent. But the real-world consequences are more complicated because climate change also alters weather patterns.
How Does Climate Change Affect Pollen Production?
Many European countries are already seeing warmer, wetter winters, hotter and drier summers, and more intense extreme weather events. Those factors affect how plants produce and release pollen. The amount of pollen that reaches allergy sufferers’ eyes and noses depends heavily on the weather.
Higher temperatures and more sunny hours early in the year have driven increases in oak pollen in recent years. Rising temperatures are also making the birch pollen season worse.
As Adams-Groom told Science Focus, if summer weather is warm, the tree pollen season the following year is likely to be harsher. How severe it becomes also depends on next year’s weather. For pollen to disperse effectively, the season needs fine weather. If it rains constantly and stays cold, the pollen grains stay trapped inside the flowers.
Grasses produce their pollen closer to the time they release it. A prolonged stretch of warm, dry days during the season can lead to many consecutive days with high pollen levels. But that can also cause grasses to deplete their pollen quickly and end the season earlier than usual.
Drier weather in early spring may mean that grasses do not produce as much pollen as they normally would. And, as Adams-Groom points out, pollen counts alone don’t fully predict how severe allergy symptoms will be on any given day.
Pollen Counts May Not Rise, But Their Potency Might
Other recent studies indicate that higher carbon dioxide levels and air pollution can increase the allergenic potency of pollen grains. That means that even if the amount of pollen in the air doesn’t rise, each grain may contain more allergy-triggering protein.
Adams-Groom says we can’t be certain yet. But it’s reasonable to assume that even if pollen counts aren’t climbing, pollen may be becoming more potent and releasing more free allergens into the atmosphere.
All of this increases the chances that hay fever seasons will worsen as the climate changes. But, as Adams-Groom cautions, like weather forecasting, the details matter. We’ll have to wait for each season to arrive before we truly know how bad (or not) allergy symptoms will be.
