The pandemic has reduced emissions from the west coast. Forest fires have already reversed it.


This is well above normal levels for this part of the year and adds to the spike in emissions caused by the massive fires in the American West in 2020. Only the fires in California produced more than 100 million tonnes of carbon dioxide last year, which was already enough to more than offset the annual decline in emissions from the wider region.

“The steady but slow reductions in [greenhouse gases] pale compared to forest fires, ”says Oriana Chegwidden, climatologist at CarbonPlan.

Massive forest fires that burn over millions of acres in Siberia are also obstruct the skies across eastern Russia and releasing tens of millions of tonnes of emissions, Copernicus reported earlier this month.

Fires and forest emissions are only expected to increase in many parts of the world as climate change accelerates over the next few decades, creating hot and often dry conditions that turn trees and plants into tinder.

Fire risk, defined as the likelihood that an area will experience a moderate to high severity fire in any given year, could quadruple in the United States by 2090, even in scenarios where emissions decline significantly. over the next few decades, according to one recent study by researchers at the University of Utah and CarbonPlan. With uncontrolled emissions, the risk of fire in the United States could be 14 times higher by the turn of the century.

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

“Very disturbing”

Over longer periods of time, the emissions and climate impacts of increased forest fires will depend on how quickly forests regrow and reduce carbon, or whether they do. This in turn depends on the dominant trees, the severity of the fires, and the extent of local climate change since this forest took root.

While preparing for her doctorate in the early 2010s, Camille Stevens-Rumann spent summer and spring months roaming the alpine forests of Frank Church-River of No Return Wilderness, Idaho, studying the aftermath of the fires.

She noted where and when the evergreen forests started to return, where they didn’t and where opportunistic invasive species like cheatgrass took over the landscape.

In one 2018 study in Ecology Letters, she and her coauthors concluded that trees that burned in the Rocky Mountains have had a much harder time regrowing this century, as the area has become hotter and drier than in the last century. end of the last one. Dry coniferous forests that had previously faltered on the brink of survival conditions were much more likely to simply convert to grass and shrub areas, which generally absorb and store much less carbon.

This can be healthy to a point, creating firebreaks that reduce damage from future fires, says Stevens-Rumann, assistant professor of forest and rangeland stewardship at Colorado State University. It may also help offset a bit of America’s history of aggressive fire suppression, which has allowed fuel to build up in many forests, also increasing the risk of major fires when they do. ‘ignite.

But their findings are “very worrying” given the massive fires we are already seeing and projections of increasingly hot and drier conditions in the American West, she said.

Other studies have noted that these pressures could begin to fundamentally transform the forests of the western United States over the next several decades, damaging or destroying sources of biodiversity, water, wildlife habitat, and forest storage. carbon.

Fires, droughts, insect infestations and changing climatic conditions will convert much of California’s forests to shrubby areas, according to a modeling study published in AGU Advances last week. Tree losses could be particularly severe in the dense forests of Douglas fir and coastal redwoods along the northern California coast and in the foothills of the Sierra Nevada range.

Kings Canyon National Park, in the Sierra Nevada range of California, 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 will continue to increase. .

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

Meanwhile, the medium to high emission scenarios create “a real probability that the forests of Yellowstone will be converted to non-forest vegetation by the middle of the 21st century”, as increasingly frequent and large fires would make more and more difficult to regrow trees. , a 2011 study in Proceedings of the National Academy of Sciences concluded.

Overall picture

The net effect of climate change on fires, and fires on climate change, is much more complex on a global scale.

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

But fires can also cause negative climate feedback. The smoke from the western forest fires that have reached the east coast in recent days, although terrible to human health, transports aerosols which reflect a certain level of heat back into space. In the same way, fires in boreal forests in Canada, Alaska and Russia can open up a space for snow that is much more reflective than the forests they replaced, thus offsetting the heating effect of the emissions released.

Different parts of the globe also push and pull in different ways.

Climate change is worsening forest fires in most forested areas around the world, says James Randerson, professor of earth system science at the University of California, Irvine and co-author of the AGU article.

But the total area burned by fires in the world is going down, mainly thanks to decreases in the savannas and grasslands of the tropics. Among other factors, farms and sprawling roads fragment the landscape in developing regions of Africa, Asia and South America, acting as brakes on these fires. Meanwhile, the growing herds of cattle gobble up fuel.

Overall, global fire emissions account for about a fifth of fossil fuel levels, although they are does not increase strongly until now. But total emissions from forests have clearly increased when including fires, deforestation and logging. They went from less than 5 billion tonnes in 2001 to more than 10 billion in 2019, according to a Climate change paper in January.

Less fuel to burn

As warming continues in the decades to come, climate change itself will affect different areas in different ways. As many regions become hotter, drier, and more susceptible to forest fires, cooler parts of the globe will become more conducive to forest growth, such as high mountains and parts of the arctic tundra, Randerson says.

Global warming could also reach a point where it would start to reduce some risks as well. If Yellowstone, California’s Sierra Nevada and other areas lose large parts of their forests, as studies suggest, fires could start to recede by the turn of the century. This is because there will simply be less or less fuel to burn.

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



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