Earth Warms, Fires Rage
In South America, the Amazon basin is ablaze. Halfway around the world in central Africa, vast stretches of savanna are going up in flames. Arctic regions in Siberia are burning at a historic pace.
While the Brazilian fires have grown into a full-blown international crisis, they represent only one of many significant areas where wildfires are currently burning around the world. Their increase in severity and their spread to places where fires were rarely previously seen are raising fears that climate change is increasing the danger.
Hotter, drier temperatures “are going to continue promoting the potential for fire,” said John Abatzoglou, an associate professor in the department of geography at the University of Idaho, describing the risk of “large, uncontainable fires globally” if warming trends continue.
Wildfires contribute to climate change because not only do they release carbon dioxide, a major greenhouse gas, into the atmosphere, but they can also kill trees and vegetation that remove climate-warming emissions from the air.
Since July, fire has charred about 2.4 million hectares of Siberian forest. In Alaska, fires have consumed more than one million hectares of tundra and snow forest, leading researchers to suggest that the combination of climate change and wildfires could permanently alter the region’s forests.
The Arctic is warming twice as fast as the rest of the planet, and some studies have noted that, as it warms, “there also is expected to be more lightning,” Dr. Abatzoglou said. In remote areas, lightning is a significant cause of fires.
One reason that Arctic wildfires are particularly concerning is that in addition to trees and grassland burning, peat also burns. Peat is a dirt-like material in the ground that, when it burns, releases much more carbon dioxide per hectare than trees do. In the past, peat fires in northern climates were rare because of moisture that is now disappearing.
The crisis in the Amazon is an example of fires being set deliberately,
A growing number of scientists are raising the alarm about a nightmare scenario that could see much of the world’s largest rainforest erased.
Climate change, along with fires and other man-made forces, appear ready to trigger a significant change in the Amazon’s weather system.
If it does happen, the Amazon would cross a tipping point and begin to self-destruct — a process of self-perpetuating deforestation called dieback.
Half or more of the rainforest could erode into savanna, and then the rainforest, which has long absorbed the world’s greenhouse gases, could instead begin to emit them.
Thomas Lovejoy, an environmental scientist, said that he and a scientist in Brazil, Carlos Nobre, had arrived at the same estimate of when it would cross that threshold: 20 to 25 percent deforestation. The Brazilian government estimates that the deforestation of the Amazon already stands at 19.3 percent, though some scientists consider this an undercount. “It’s really close,” Dr. Lovejoy said.
The world may look back and find the warnings of ecological catastrophe embedded in papers like one led by Jennifer Balch, an expert on fire.
Before Jair Bolsonaro, the president of Brazil, oversaw this summer’s drastic increase in man-made fires in the rainforest, Dr. Balch and her colleagues set out to study what was then a rarer phenomenon.
They subjected plots of rainforest to a decade of small but repeated fires like those set by farmers. After enough cycles, even if the fires caused only moderate damage, if rainfall dropped, the trees began dying off in huge numbers. The proportion of plant life that died after a fire suddenly spiked from 5 or 10 percent to 60 percent — sudden ecological death.
“The Amazon does have a tipping point,” Dr. Balch said. “And it can happen in a very short period of time.”
This process seemed to fit into a larger cycle — one that implicated the whole rainforest, triggered by four man-made forces: roads, fires, invasive grasses and climate change.
“You’re exposing a lot more forest edges,” Dr. Balch said.
Those edges are more susceptible to drying out and other dangers. Invasive grasses are one of those dangers, lingering at forest edges. Even a small fire can wipe out undergrowth. Grasses rush in, setting a blanket of flammable plant life, making the next fire worse.
Climate change, by heating the Amazon, has made its dry seasons dryer and more hospitable to those grasses. What makes those forces so dangerous is not that they kill trees — it is that they reduce rainfall. In a healthy rainforest, plant life absorbs rainwater and groundwater, then sweats it back out into the atmosphere as moisture, seeding more rain.
Once the dieback cycle begins, it would likely only accelerate.
A tipping point for ecological disaster is ‘really close.’