Microbes in trees remove methane from the atmosphere

As methane levels hit their highest point in 800,000 years, an international team of researchers has discovered that microbes living on trees can actually absorb methane gas from the atmosphere. Their breakthrough has been published in the journal Nature.

Methane is responsible for around 30% of global warming since pre-industrial times and emissions are currently rising faster than at any point since records began in the 1980s, directly as a result of human activity. But although most methane is removed by processes in the atmosphere, soils are full of bacteria that absorb the gas and break it down for use as energy. Soil had previously been thought of as the only terrestrial sink for methane, but trees may be just as important — perhaps more so.

The research team, led by the University of Birmingham, took measurements spanning tropical forests in the Amazon and Panama; temperate broadleaf trees in Wytham Woods, UK; and boreal coniferous forest in Sweden. By studying methane exchange between the atmosphere and the tree bark at multiple heights, they were able to show that while at soil level the trees were likely to emit a small amount of methane, from a couple of metres up the direction of exchange switches and methane from the atmosphere is consumed.

On average, the newly discovered methane absorption adds around 10% to the climate benefit that temperate and tropical trees provide. Absorption was strongest in the tropical forests, probably because microbes thrive in the warm wet conditions found there.

In addition, the team used laser scanning methods to quantify the overall global forest tree bark surface area, with preliminary calculations indicating that the total global contribution of trees is between 24.6 and 49.9 Tg (millions of tonnes) of methane. Tree shape analysis shows that if all the bark of all the trees of the world were laid flat, the area would be equal to the Earth’s land surface.

The Birmingham researchers are now planning to investigate if deforestation has led to increased atmospheric methane concentrations. They also aim to understand more about the mechanisms used by the microbes to take up the methane, and will investigate if this atmospheric methane removal by trees can be enhanced.

“The main ways in which we consider the contribution of trees to the environment is through absorbing carbon dioxide through photosynthesis and storing it as carbon,” said lead researcher Professor Vincent Gauci. “These results, however, show a remarkable new way in which trees provide a vital climate service.

“The Global Methane Pledge, launched in 2021 at the COP26 climate change summit, aims to cut methane emissions by 30% by the end of the decade. Our results suggest that planting more trees and reducing deforestation surely must be important parts of any approach towards this goal.”

Image credit: iStock.com/jotily