Climate change

Do you have allergies? Climate change is making the pollen season longer and longer

By Yingxiao Zhang and Allison L. Steiner 5 minutes Read

Get ready, allergy sufferers – new research shows that the pollen season is going to get much longer and more intense with climate change.

Our latest research reveals that the United States will face up to 200% increase in this century’s total pollen if the world continues to produce carbon dioxide emissions from vehicles, power plants and other sources at a high rate. The pollen season in general will start up to 40 days earlier in the spring and last up to 19 days longer than today in this scenario.

As atmospheric scientists, we study how the atmosphere and climate affect trees and plants. While most studies focus on pollen as a whole, we have zoomed in on more than one a dozen different types of grasses and trees and how their pollen will affect regions of the United States in different ways. For example, species like oak and cypress will give the biggest increase in the northeast, but allergens will be up pretty much everywhere, with consequences for human health and the economy.

If your head is pounding at the mere thought, we also have good news, at least to know in advance when the pollen waves are coming. We are working on using the model from this study to develop more accurate local pollen forecasts.

Why pollen increases

Let’s start with the basics. Pollen – the dust-like grains produced by grasses and plants – contains the male genetic material for a plant’s reproduction.

The amount of pollen produced depends on how the plant grows. Rising global temperatures will stimulate plant growth in many regions, which in turn will affect pollen production. But temperature is only part of the equation. We found that the biggest driver of future pollen increases will increase carbon dioxide emissions.

The higher temperature will extend the growing season, giving plants more time to shed pollen and reproduce. Carbon dioxide, on the other hand, fuels photosynthesis, so plants can get bigger and produce more pollen. We found that carbon dioxide levels could have a much bigger impact on pollen increases than temperature in the future.

The maps on the left show the recent average length of the pollen season in days for three types of plants: plane trees, or plane trees, such as sycamores; betula or birch; and ambrosia, or ragweed. The maps on the right show the expected changes in the total number of days by the end of the century if carbon dioxide emissions continue at a high rate. [Photo: The Conversation]

Pollen changes will vary by region

We looked at 15 different types of pollen, rather than treating all pollens the same as many previous studies.

Typically, pollination begins with broadleaf deciduous trees in late winter and spring. Alder, birch and oak are the three deciduous trees that cause the most allergies, although there are others, such as mulberry. Then the grasses come out in summer, followed by ragweed in late summer. In the southeast, evergreens like mountain cedar and juniper (from the cypress family) start in January. In Texas, “cedar fever” is the equivalent of hay fever.

We found that in the northeast, the pollen seasons for many allergenic trees ride more and more as temperatures and carbon dioxide emissions increase. For example, in the past, the oaks first released pollen, then the birches pollinated. Now we see more overlap of their pollen seasons.

In general, the pollen season will change more in the north than in the south, due to greater temperature increases in northern regions.

Southeast regions, including Florida, Georgia and South Carolina, can expect large increases in grass and weed pollen in the future. The Pacific Northwest will likely experience the peak of the pollen season a month earlier due to the early alder pollen season.

Silver lining: we can improve pollen forecasts

Most pollen forecasts currently provide a very broad estimate. Part of the problem is that there are not many observation stations for pollen count. Most are run by allergy clinics, and there are less than 100 such stations spread across the country. Michigan, where we live, has none.

It is a very laborious process to measure different types of pollen. As a result, current forecasts are subject to many uncertainties. These are likely based in part on what a station has observed in the past and on weather forecasts.

Our model, if integrated into a forecasting framework, could provide more targeted pollen forecasts across the country.

We can estimate where the trees are from satellite data and field surveys. We also know how temperature influences pollen egress, what we call pollen phenology. With this information, we can use weather factors like wind, relative humidity and precipitation to determine how much pollen is getting into the air, and atmospheric models can show how it moves and blows, to create a real-time forecast.

All of this information allows us to see where the pollen might be in space and time, so allergy sufferers know what’s going on in their area.

We are currently talking with a The National Oceanic and Atmospheric Administration laboratory on ways to integrate this information into an air quality forecasting tool.

There are still some unknowns when it comes to long-term pollen projections. For example, scientists don’t fully understand why plants produce more pollen in some years than others. There is no good way to include this in templates. It’s also unclear how plants will react if carbon dioxide levels soar. Ragweed and residential trees are also difficult to capture. There are very few ragweed surveys showing where these plants grow in the United States, but that can be improved upon.