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.