The pandemic dramatically reduced emissions from the West Coast. Forest fires have already reversed it.


That is well above normal levels for this part of the year and adds to the increase in emissions from mass fires across the American West in 2020. Only the California fires produced more than 100 million tons of carbon dioxide last year, which was already enough to more than offset the region’s annual emission reductions as a whole.

“The steady but slow reductions in [greenhouse gases] they pale in comparison to wildfires, ‚ÄĚsays CarbonPlan climate scientist Oriana Chegwidden.

Massive wildfires burning over millions of acres in Siberia are also obstructing the skies in eastern Russia and releasing tens of millions of tons of emissions, Copernicus reported earlier this month.

Forest fires and emissions are only expected to increase in many regions of the world as climate change accelerates in the coming decades, creating the warm and often dry conditions that turn trees and plants to tinder.

Fire risk, defined as the probability that an area will experience a moderate to high intensity fire in a given year, could quadruple in the US By 2090, even in scenarios where emissions decline significantly over the next few decades, according to a recent study by researchers at the University of Utah and CarbonPlan. If emissions are not controlled, the risk of fire in the US could be 14 times greater by the end of the century.

Emissions from the fires “are already bad and are only going to get worse,” says Chegwidden, one of the study’s lead authors.

“Very sinister”

Over longer periods of time, the emissions and climate impacts of increased wildfires will depend on how quickly forests grow back and reduce carbon, or if they do so. That, in turn, depends on the dominant trees, the severity of the fires, and how much local weather conditions have changed since the forest took root.

While working toward her Ph.D. in the early 2010s, Camille Stevens-Rumann spent the summer and spring months touring alpine forests in Idaho’s Frank Church – River of No Return Wilderness, studying the aftermath of the fires.

He pointed out where and when coniferous forests began to return, where they did not, and where opportunistic invasive species like cheat grass took over the landscape.

in a Study 2018 In Ecology Letters, she and her co-authors concluded that the trees that burned in the Rocky Mountains have had much more trouble growing this century, as the region has become warmer and drier than during the end of the last. Dry coniferous forests that had already teetered on the brink of survival conditions were much more likely to simply become pastures and shrubs, which generally absorb and store much less carbon.

This can be healthy to some extent, creating firebreaks that reduce damage from future fires, says Stevens-Rumann, assistant professor of forest and grassland management at Colorado State University. It can also help offset a bit of the US history of aggressively putting out fires, which has allowed fuel to build up in many forests, also increasing the chances of large fires breaking out when they do ignite.

But his findings are “very sinister” given the massive fires we are already seeing and projections of increasingly warmer and drier conditions across the western United States, he says.

Other studies have pointed out that these pressures could begin to fundamentally transform the forests of the western United States in the coming decades, damaging or destroying sources of biodiversity, water, wildlife habitat and carbon storage.

Fires, droughts, insect infestations and changing weather conditions will turn most of California’s forests into scrub, according to a modeling study published in AGU Advances last week. Tree loss could be particularly pronounced in the dense Douglas fir and coastal redwood forests along the northern California coast and in the foothills of the Sierra Nevada mountain range.

Kings Canyon National Park after a forest fire
Kings Canyon National Park, in California’s Sierra Nevada mountain range, following a recent wildfire.

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In total, the state will lose about 9% of the carbon stored in trees and plants on the surface by the end of this century in a scenario in which we stabilize emissions this century, and more than 16% in a future world where they continue increasing. .

Among other impacts, that will clearly complicate the state’s reliance on its lands to capture and store carbon through its forest offset program and other climate efforts, the study notes. California is striving to become carbon neutral by 2045.

Meanwhile, medium to high emission scenarios create “a real probability that Yellowstone forests will become non-forest vegetation during the mid-21st century,” because increasingly common and large fires would make it increasingly difficult for them to trees grow back. , a 2011 study in Proceedings of the National Academy of Sciences concluded.

The global picture

The net effect of climate change on fires and fires on climate change is much more complicated globally.

Fires contribute directly to climate change by releasing emissions from trees, as well as the rich carbon stored in soils and peatlands. They can also produce black carbon that can eventually settle on glaciers and ice sheets, where it absorbs heat. That accelerates the loss of ice and the rise in ocean levels.

But fires can also generate negative climate feedback. Smoke from the western wildfires that reached the east coast in recent days, though dire for human health, carries sprays that reflect a certain level of heat back into space. Similary, boreal forest fires in Canada, Alaska and Russia they can open up space for snow that is much more reflective than the forests they replaced, offsetting the warming effect of released emissions.

Different parts of the world are also pushing and pulling in different ways.

Climate change is making wildfires worse in most of the world’s forested areas, says James Randerson, professor of earth system science at the University of California, Irvine, and a co-author of the AGU paper.

But the total area burned by fires worldwide is really going down, mainly thanks to the decrease in the savannas and grasslands of the tropics. Among other factors, sprawling farms and roads are fragmenting the landscape in developing parts of Africa, Asia and South America, acting as a brake on these fires. Meanwhile, growing cattle herds are gobbling up fuel.

Overall, global emissions from fires account for about a fifth of fossil fuel levels, although they are not rising sharply yet. But total emissions from forests have clearly increased when fires, deforestation and logging are included. They have grown from less than 5 billion tons in 2001 to more than 10 billion in 2019, according to a Nature climate change document in January.

Less fuel to burn

As warming continues for decades to come, climate change itself will affect different areas in different ways. While many regions will become warmer, drier and more susceptible to wildfires, some colder parts of the world will become more hospitable to forest growth, such as high mountains and parts of the Arctic tundra, Randerson says.

Global warming could also reach a point where it actually begins to reduce certain risks. If Yellowstone, California’s Sierra Nevada and other areas lose large portions of their forests, as studies have suggested, fires could begin to subside by the end of the century. That’s because there will simply be less fuel or less flammable to burn.

It’s difficult to make reliable predictions about global emissions from forests and fires in the coming decades because there are so many competing variables and unknowns, in particular, including the actions humans will decide to take, says Doug Morton, head of the biospheric science lab at the NASA’s Goddard Space. Flight center.


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