🔥 Fires: a 2000-year trend has reversed

It's a break in the curves: a notable increase in fires has just been discovered in tropical peatlands. While their frequency had continuously decreased for over a millennium, it has sharply increased over the last hundred years. This reversal of trend, documented by a new study, coincides with the intensification of human activities in these regions.

To trace this history, researchers analyzed charcoal fragments preserved in peat layers over two thousand years. These samples, from areas in Central and South America, Africa, Southeast Asia, and Australasia, show that fires were once mainly linked to dry climatic conditions. The results, published in Global Change Biology, indicate a gradual decline in fire activity over more than a thousand years.


This long period of decline ended in the 20th century, with a rapid rise in the number of fires. This clear break with the past shows that other factors, different from climate, now come into play.

The increase is very pronounced in Southeast Asia and parts of Australasia. In these areas, draining peatlands for agriculture, deforestation, and urbanization dry out the soils, making them easier to ignite. These practices alter the natural balance and increase the risks.

In contrast, peatlands in South America and Africa, generally more isolated, have not experienced the same intensification. Nevertheless, with population growth and economic development, these regions could become more exposed in the future.

These ecosystems store considerable amounts of carbon, even surpassing all the world's forests. When they burn, this carbon is released into the atmosphere, contributing to global warming.

The role of peatlands in the carbon cycle

Peatlands form in wet environments where dead vegetation decomposes very slowly, accumulating organic matter rich in carbon over thousands of years. This process generates peat layers that act as sinks capturing atmospheric carbon dioxide.

These environments are particularly effective for storage because stagnant water slows microbial activity and decomposition. The carbon thus remains trapped in the soil. When peatlands are drained or burned, the stored carbon is released as carbon dioxide and other greenhouse gases, which can accelerate warming.

Human factors behind the increase in fires

The expansion of human activities in the tropics has profoundly changed peatland landscapes. Drainage for agriculture, for example, dries out soils and makes them more flammable during droughts. Moreover, land conversion for plantations or urban development fragments these ecosystems and reduces their natural resistance to fire.

In Southeast Asia, where the increase is most pronounced, controlled burns to prepare fields can also degenerate into uncontrollable fires. The interaction between drought and these human activities has created conditions conducive to the conflagration observed last century.