A fire burns a field on a farm in the Nova Santa Helena municipality, in the state of Mato Grosso, Brazil.

The thousands of fires burning in the Amazon don't look like the major forest fires of Europe or North America -- instead, they are fueled mainly by branches, vegetation and other byproducts of deforestation in cleared areas, experts say.

The dramatic scale of this year's fires is the result of a significant acceleration of deforestation for the lumber industry, for agriculture or for other human activities.

"In the tropics, fire is used extensively in a land-use environment," said Jeffrey Chambers, a scientist at the Lawrence Berkeley National Laboratory and a specialist in rainforests.

But in the Amazon, when an area of forest is cleared, the tree trunks are removed and the rest of the vegetation is burned on the spot during the dry season, which lasts from July to November.

Neri dos Santos Silva watches an encroaching fire threat after digging trenches to keep the flames from spreading to the farm.

Trend reversal

The fires have made the deforestation visible, according to Paulo Brando, an assistant professor at the University of California, Irvine and a scientist at the Woods Hole Research Center.

"You can see the fires as the final phase of deforestation," he said.

Additionally, the dry season isn't over. Will the fires bite into intact forest?

"Right now, we are seeing mostly increases in deforestation-related fires, which may or may not escape into primary forests, depending on how dry it's going to get in the next few months," said Brando.

Small columns of smoke rise from the forest near Porto Velho, Brazil.

And how will that affect climate change?

Forests contain carbon, stored in the trees and vegetation -- to the tune of 459 tonnes per hectare in the Amazon, said Diego Navarrete, a carbon specialist at the NGO The Nature Conservancy.

When a tree is cut, the carbon inside will reenter the atmosphere years later, at the end of its use cycle when it decomposes. When vegetation is burned, as is happening now, the carbon enters the atmosphere immediately.

In both cases, the carbon will be released. It just takes some simple math to realize that the total for the past few months has already reached hundreds of millions of tonnes of carbon.

Agence France-Presse