Drought leaches carbon from Amazon

5 February 2014 by Alex Peel

A drought in 2010 caused the Amazon basin to release more carbon into the atmosphere than it took in, new research has revealed.

Amazon jungle alightThe study, published in Nature, says smoke from wildfires sparked by the dry conditions was the main reason for the losses.

But the lack of moisture also seems to have triggered a slowdown in photosynthesis, the process by which plants draw carbon in from the atmosphere.

As the climate of the Amazon warms and the forest experiences more severe flooding and droughts, these processes could become more permanently established.

In effect, the world's biggest rainforest, often referred to as 'the lungs of the world' because of its ability to absorb carbon from the atmosphere and pump out oxygen, would become a net carbon source.

"You can think of it like a bank account," says Professor Emanuel Gloor from the University of Leeds, one of the study's authors. "If you have the same amount of carbon coming into the system as is going out, then the system is in balance."

It's a warning - it shows that the forest is changing

- Professor Emanuel Gloor, University of Leeds

"But if the outgoings start to exceed the income, then you lose carbon from the forest."

The Amazon basin lies beneath a river of air flowing across South America from the Atlantic in the East, before turning south as it hits the Andes in the West and then back out to the Atlantic.

The international team used sampling equipment attached to light aircraft to measure the greenhouse gases in the atmosphere. By taking samples at the eastern and western edges of the basin, they estimated how much carbon came in and out of the air river as it passed over.

A wildfire burns slowly through the understorey of an Amazonian forest

A wildfire burns slowly through the understorey of an Amazonian forest.

The research was carried out across 2010 and 2011, which happened to be a dry year followed by a wet year. This gave the scientists a unique opportunity to investigate the influence of rainfall over the carbon balance of the basin.

Following the carbon losses of 2010, the forest seemed to recover well in 2011, broadly returning to normal conditions.

Recent studies using computer models have suggested that heat holds the key, but temperatures here were similar between the two years.

The picture in the Amazon reflects the global pattern of a stalling in the tropics' take-up of carbon from the atmosphere. This is currently being offset by increasing carbon take-up on land outside of the tropics, explains Gloor.

But the future of the Amazon rainforest itself, home to the richest diversity of animals and plants on Earth, seems far from secure.

"We cannot say yet whether the forest will switch to another system where it is losing carbon year on year," he says. "But if this happens too often, the forest will suffer."

"It's a warning - it shows that the forest is changing."