If you’re feeling the misery of allergy season in your sinuses and throat, you’re probably wondering what nature has in store for you this time – and in the future.

Pollen allergies affect over 30% of the global population, making them a significant public health and economic issue as people feel ill and miss work. Our research shows that, as greenhouse gases warm the planet, their effects are driving longer and more intense pollen seasons.

To help allergy sufferers manage their symptoms in our changing climate, we’re building better pollen forecasts for the future.

As atmospheric scientists, we study how the atmosphere and climate affect trees and plants. In a 2022 study, we found that the U.S. will face up to a 200% increase in total pollen this century if the world continues producing carbon dioxide emissions at a high rate. Pollen season in general will start up to 40 days earlier in the spring and last up to 19 days longer than today under that scenario.

While most studies focus on pollen overall, we zoomed in on more than a dozen different types of grasses and trees and how their pollen will affect regions across the U.S. in different ways. For example, species like oak and cypress will give the Northeast the biggest increase, but allergens will be on the rise just about everywhere, with consequences for human health and the economy.

Why pollen is increasing

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

How much pollen 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.

Warmer temperatures will extend the growing season, allowing plants to grow and emit pollen for longer periods. But temperature is only part of the equation. We found that a potentially greater driver of the future pollen increase will be rising carbon dioxide emissions from sources such as vehicles and power plants. Carbon dioxide fuels photosynthesis, leading to increased growth and the potential for more pollen production.

Pollen changes will vary by region

We looked at 15 different pollen types, rather than treating all pollen the same as many past studies have. Our study found that the amount of pollen increase in a specific region depends on the types of vegetation.

Typically, pollination starts with leafy deciduous trees in late winter and spring. Alder, birch and oak are the three top deciduous trees for causing allergies, though there are others, like mulberry. Grass pollen becomes more prevalent in the summer, followed by ragweed in late summer. In the Southeast, evergreen trees like mountain cedar and juniper (in the cypress family) start in January. In Texas, “cedar fever” is the equivalent of hay fever.

We found that in the Northeast, pollen seasons for a lot of allergenic trees will increasingly overlap as temperatures and carbon dioxide emissions rise. For example, it used to be that maple trees would release pollen first, and then birch would pollinate. Now we see more overlap of their pollen seasons.

In general, pollen season changes are greater in the northern United States than in the South, because of larger temperature increases in northern areas in future climate projections.

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

Allergy problems are already on the rise. A study in 2021 found that the overall pollen season was already about 20 days longer in North America than it was in 1990 and pollen concentrations were up about 21%.

Silver lining: We can improve pollen forecasting

Most pollen forecasts right now provide a very broad estimate of where and when pollen counts will be high. Part of the problem is that there aren’t many observing stations for pollen counts. Most are run by allergy clinics, and there are fewer than 200 of these stations distributed across the country. Michigan, where we live, doesn’t have any that are currently operating.

It’s a very labor-intensive process to measure different types of pollen. As a result, current forecasts have a lot of uncertainties. These likely are based in part on what a station has observed in the past and the weather forecast.

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 on-the-ground surveys. We also know how temperature influences when pollen comes out – what scientists call the phenology of the pollen. With that information, we can use meteorological factors like wind, relative humidity and precipitation to figure out how much pollen gets into the air, and atmospheric models can show how it moves and blows around, to create a real-time forecast.

We’re currently working with a National Oceanic and Atmospheric Administration lab about ways to integrate that information into a tool for air quality forecasting. Our next step is to evaluate these forecast tools and make information available to the public.

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, and currently we cannot include these changes in our models. It’s also not fully clear how plants will respond if carbon dioxide levels go through the roof. Ragweed and residential trees are also hard to capture. There are very few ragweed surveys showing where these plants are growing in the U.S., but that can be improved.

This is an update to an article originally published March 15, 2022.

Yingxiao Zhang, Ph.D. Student in Atmospheric Science, University of Michigan and Allison L. Steiner, Professor of Atmospheric Science, University of Michigan

This article is republished from The Conversation under a Creative Commons license. Read the original article.

As wildfire risk rises in the West, wildland firefighters and officials are keeping a closer eye on the high mountains – regions once considered too wet to burn.

The growing fire risk in these areas became startling clear in 2020, when Colorado’s East Troublesome Fire burned up and over the Continental Divide to become the state’s second-largest fire on record. The following year, California’s Dixie Fire became the first on record to burn across the Sierra Nevada’s crest and start down the other side.

We study wildfire behavior as climate scientists and engineers. In a new study, we show that fire risk has intensified in every region across the West over the past four decades, but the sharpest upward trends are in the high elevations.

High mountain fires can create a cascade of risks for local ecosystems and for millions of people living farther down the mountains.

Since cooler, wetter high mountain landscapes rarely burn, vegetation and dead wood can build up, so highland fires tend to be intense and uncontrollable. They can affect everything from water quality and the timing of meltwater that communities and farmers rely on, to erosion that can bring debris and mud flows. Ultimately, they can change the hydrology, ecology and geomorphology of the highlands, with complex feedback loops that can transform mountain landscapes and endanger human safety.

Four decades of rising fire risk

Historically, higher moisture levels and cooler temperatures created a flammability barrier in the highlands. This enabled fire managers to leave fires that move away from human settlements and up mountains to run their course without interference. Fire would hit the flammability barrier and burn out.

However, our findings show that’s no longer reliable as the climate warms.

We analyzed fire danger trends in different elevation bands of the Western U.S. mountains from 1979 to 2020. Fire danger describes conditions that reflect the potential for a fire to ignite and spread.

Over that 42-year period, rising temperatures and drying trends increased the number of critical fire danger days in every region in the U.S. West. But in the highlands, certain environmental processes, such as earlier snowmelt that allowed the earth to heat up and become drier, intensified the fire danger faster than anywhere else. It was particularly stark in high-elevation forests from about 8,200 to 9,800 feet (2,500-3,000 meters) in elevation, just above the elevation of Aspen, Colorado.

We found that the high-elevation band had gained on average 63 critical fire danger days a year by 2020 compared with 1979. That included 22 days outside the traditional warm season of May to September. In previous research, we found that high-elevation fires had been advancing upslope in the West at about 25 feet (7.6 meters) per year.

Cascading risks for humans downstream

Mountains are water towers of the world, providing 70% of the runoff that cities across the West rely on. They support millions of people who live downstream.

High-elevation fires can have a significant impact on snow accumulation and meltwater, even long after they have burned out.

For example, fires remove vegetation cover and tree canopies, which can shorten the amount of time the snowpack stays frozen before melting. Soot from fires also darkens the snow surface, increasing its ability to absorb the Sun’s energy, which facilitates melting. Similarly, darkened land surface increases the absorption of solar radiation and heightens soil temperature after fires.

The result of these changes can be spring flooding, and less water later in the summer when communities downstream are counting on it.

Fire-driven tree loss also removes anchor points for the snowpack, increasing the frequency and severity of avalanches.

Frequent fires in high-elevation areas can also have a significant impact on the sediment dynamics of mountain streams. The loss of tree canopy means rainfall hits the ground at a higher velocity, increasing the potential for erosion. This can trigger mudslides and increase the amount of sediment sent downstream, which in turn can affect water quality and aquatic habitats.

Erosion linked to runoff after fire damage can also deepen streams to the point that excess water from storms can’t spread in high-elevation meadows and recharge the groundwater; instead, they route the water quickly downstream and cause flooding.

Hazards for climate-stressed species and ecosystems

The highlands generally have long fire return intervals, burning once every several decades if not centuries. Since they don’t burn often, their ecosystems aren’t as fire-adapted as lower-elevation forests, so they may not recover as efficiently or survive repeated fires.

Studies show that more frequent fires could change the type of trees that grow in the highlands or even convert them to shrubs or grasses.

Wet mountain areas, with their cooler temperatures and higher precipitation, are often peppered with hot spots of biodiversity and provide refuges to various species from the warming climate. If these areas lose their tree canopies, species with small ranges that depend on cold-water mountain streams can face existential risks as more energy from the Sun heats up stream water in the absence of tree shading.

While the risk is rising fastest in the high mountains, most of the West is now at increasing risk of fires. With continuing greenhouse gas emissions fueling global warming, this trend of worsening fire danger is expected to intensify further, straining firefighting resources as crews battle more blazes.

Mohammad Reza Alizadeh, Postdoctoral Researcher in Environmental Engineering, Massachusetts Institute of Technology (MIT) and Mojtaba Sadegh, Assistant Professor of Civil Engineering, Boise State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.