The growing intensity of wildfires and their spread to new corners of the globe raises fears that climate change is exacerbating the dangers.
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In South America, the Amazon basin is ablaze. Halfway around the world in central Africa, vast stretches of savanna are going up in flame. 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 spread to places where fires were rarely previously seen is raising fears that climate change is exacerbating 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.
This year has so far seen a dramatic increase in wildfires in some arctic regions that traditionally rarely burned.
Since July, fire has charred about six million acres of Siberian forest, an area roughly the size of the state of Vermont. In Alaska, fires have consumed more than 2.5 million acres 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,” said Dr. Abatzoglou, and in remote areas, lightning is a significant cause of fires.
And though the Amazon is widely described as the world’s lungs, a reference to the forest’s ability to produce oxygen while storing carbon dioxide, forests like those in Siberia are as important to the global climate system as tropical rainforests.
One reason that arctic wildfires are particularly concerning is that in addition to trees and grassland burning, peat also burns, a dirt-like material in the ground itself that releases much more carbon dioxide when it burns than do trees per acre of fire. In the past, peat fires in northern climates were rare because of moisture that is now disappearing as the region becomes warmer and drier.
For reasons of geography, economics, politics and climate, there is no simple way to categorize wildfires — each one is different, and may represent a mix of root causes.
“We have the intentional fires, through land clearing. We have the fires that are happening in remote areas that probably wouldn’t be happening, at least at this severity, in the absence of climate change,” said Dr. Abatzoglou.
Around the world, these forces sometimes interact in strikingly different ways.
The Amazon and Indonesia: Intentionally Set Fires
The crisis in the Amazon is an example of fires being set deliberately, to clear forested land for farming or the grazing of livestock. In Brazil’s case, this is driven by a global demand for soybeans and cattle, particularly as China has gotten wealthier and people are more able to afford meat.
Between 2004 and 2012, deforestation in the region had been on the decline, but that changed in 2013. Jair Bolsonaro, who last year was elected Brazil’s president, has championed the expansion of the farming industry and has dismissed the idea of extending protections to indigenous groups that live in the forest, which has led to worries that deforestation rates could further increase.
Early reports suggest that this year’s burnings, which coincide with the Amazon’s dry season, are poised to worsen in part because the United States’ trade war with China — one of the world’s biggest soybean buyers — has driven Beijing to find new suppliers to replace American farmers. Still, “We don’t know yet how much area has been actually burned,” cautioned Laura C. Schneider, an associate professor in the department of geography at Rutgers University.
Indigenous communities in the Amazon have used fire in the rainforests for generations, though they tend to cultivate much smaller areas, plant a relatively diverse number of crops and move onto a new plot of land after a few years, allowing the forest to regrow.
“It’s important to mention that they are able to control those fires. And again, the unusual thing right now is that these fires are a little bit out of control,” said Dr. Schneider.
That is different from what is currently happening in the Amazon, where today’s more industrialized agriculture means that deforested land tends to remain permanently cleared. This land still sometimes burns, however: Farmers will often clear a field for a new crop by burning the stubble from the previous crop, and that explains many of the fires burning now.
A similar pattern is playing out in Southeast Asia, where 71 percent of peat forests have been lost across Sumatra, Borneo and peninsular Malaysia between 1990 and 2015. In many cases the forests were replaced by farms that produce palm oil, which is used in everything from cookies to cologne and is one of the most important crops in the region.
In 2015, the smog and haze from the peatland fires were so severe that it may have led to the premature death of 100,000 people, according to a study released the following year. In the wake of that year’s haze, the government adopted a number of measures to reduce the number of fires, but this year, the haze is back.
The Arctic: A New Tinder Box
Even though both involve the burning of peat, the fires in Indonesia are quite distinct from what is happening in the northern reaches of the globe, including the Arctic. This summer, wildfires broke out across the region — including Alaska, Greenland and Siberia, in places that have not typically burned in the past.
The fires are driven by rising temperatures, which dry out plants and make them more likely to ignite. Many researchers describe the heat as a signal of climate change in a region of the world that has warmed more quickly than the rest of the planet. This summer, for example, parts of Alaska broke records: Anchorage reached a high of 90 degrees on July 4 when average temperatures for that date are 75 degreeS.
As these fires have spread, so too have their carbon dioxide emissions, which reached their highest levels since satellite record-keeping began in 2003.
Over the first 18 days of August alone, Arctic wildfires emitted 42 megatons of carbon dioxide. That brought the total for June, July, and the first part of August to more than 180 megatons, roughly three and a half times more than the country of Sweden emits in a year.
Not only are the fires widely seen as a signal of climate change, but they can also exacerbate global warming because of the soot produced by burning peat, which is rich in carbon. When the soot settles on nearby glaciers, the ice absorbs the sun’s energy instead of reflecting it, speeding up the melting of the glacier.
California and Africa: The Seasonal Cycle of Burning
While the fires that struck the Arctic this summer are unusual, not all wildfires are nearly so unexpected. In some places, there is a seasonal cycle of burning that plays a major role.
The American west is one example.
It is true globally that humans trigger most wildfires, whether accidentally through a dropped cigarette or campfire, or intentionally to clear land. However, one reason places like California seemingly have wildfires every year is because the state, along with much of the West and Southeastern United States, are what researchers call fire-adapted ecosystems.
In other words, some landscapes have evolved over time to not only tolerate fire, but actually need it. For instance, lodgepolepines, a staple tree of the Western United States, need the heat from wildfires to release their seeds.
A similar pattern can be seen in some of the sub-Saharan African fires that have recently drawn the world’s attention. According to Dr. Abatzoglou, the savanna ecosystems just north and south of Africa’s tropical rainforest burn fairly predictably every two to three years.
“This is really the most fire-prone ecosystem globally,” he said. “It’s the right combination of it being wet enough to have enough fuel and dry enough to burn, and there’s plenty of lightning.”
Still, climate change can have a dramatic effect on wildfires even in these parts of the world. For instance, research published this year suggests that California’s wildfires are 500 percent larger than they would be without human-induced climate change.