Climate change affects allergy sufferers: scientists anticipate longer pollen seasons

A recent study found that the US will face a 200% increase in total pollen this century if the world continues to produce carbon dioxide emissions from vehicles, power plants and other sources at a high rate. The pollen season will generally begin up to 40 days earlier in the spring and will last up to 19 days longer than usual.

“We study how the atmosphere and climate affect trees and plants. While most studies focus on pollen in general, we focus on more than a dozen different types of grasses and trees and how their pollen will affect U.S. regions in different ways,” explained Yingxiao Zhang, a specialist in the Department of Climate and Space Science and Engineering at the University of Michigan and first author of the document that has just been published in the scientific journal Nature.

The researchers found that, for example, species such as oak and cypress will give the northeast the largest increase in their presence in the country, but allergens will increase almost everywhere, with consequences for human health and the economy.

Scientists, in addition to warning about the event, are concerned that they can establish a more accurate timetable that will allow, at least, to know in advance when the pollen waves will arrive. “We are working on using this study's model to develop more accurate local pollen forecasts,” the researcher said.

Pollen, the dust-like grains produced by grasses and plants, contains the male genetic material for the reproduction of a plant. The amount that is produced depends on how the plant grows . Rising global temperatures will boost plant growth in many areas and that, in turn, will affect pollen production. But temperature is only part of the equation. “We found that the biggest driver of future pollen growth will be increased carbon dioxide emissions,” says Yingxiao.

The higher temperature will extend the growing season, giving the flora more time to emit pollen and reproduce. Meanwhile, carbon dioxide fuels photosynthesis, so plants can grow and produce more pollen. Specialists found that carbon dioxide levels can have a much greater impact on pollen increases than temperature in the future.

Volatile cadence

Specialists looked at 15 different types of pollen, rather than treating all pollen in the same way as many previous studies. Usually, pollination begins with leafy deciduous trees in late winter and spring. In the US, alder, birch and oak are the three main deciduous trees that cause allergies, although there are others, such as mulberry. Then the pastures come out in the summer, followed by ambrosia at the end of that season. In the southeast, evergreens such as mountain cedar and juniper (from the cypress family) begin in January. In fact, in Texas, cedar fever is the equivalent of hay fever.

“We found that in the Northeast, pollen seasons for many allergenic trees will increasingly overlap as temperatures and carbon dioxide emissions increase. For example, before oaks released pollen first, and then birches pollinated. We now see more overlap from their pollen seasons,” the researchers said.

According to the predictions of this study, they predict that, in general, the pollen season will change more in the north than in the southern United States, due to higher temperature increases in the northern areas. Southeastern regions, including Florida, Georgia and South Carolina, can expect large increases in grass and weed pollen in the future, the document predicts. The Pacific Northwest is likely to see peak pollen season a month earlier due to the early alder season.

Most pollen forecasts at this time give a very broad estimate. Part of the problem is that there aren't many observation stations for pollen counting. Most are run by allergy clinics, and there are fewer than 100 of these stations spread across the country. “It is a very laborious process to measure different types of pollen,” Yingxiao said. As a result, current forecasts have many uncertainties. These are likely to be based in part on what a station has observed in the past and on the weather forecast. Our model, if integrated into a forecasting framework, could provide more targeted pollen forecasts across the country.”

The scholars of this paper believe that it is possible to estimate where trees are based on satellite data and field studies. They also know how temperature influences when pollen comes out, what they call pollen phenology. With that information, they can use weather factors such as wind, relative humidity, and precipitation to determine how much pollen reaches the air, and atmospheric models can show how it moves and blows, to create a real-time forecast. All that information allows you to see where pollen might be in space and time, so that people with allergies know what's going on in their area.

There are still some unknowns about long-term pollen projections. For example, scientists don't fully understand why plants produce more pollen in some years than in others. There's no good way to include that in the models. It is also not entirely clear how plants will respond if carbon dioxide levels skyrocket, and residential trees are also difficult to capture. There are very few ragweed surveys that show where these plants grow in the US, but that can be improved.

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