While trees are well known for sucking carbon dioxide from the atmosphere, researchers have discovered they offer one more important benefit: They can act as a net sink of methane, another gas that harms the planet.
That means trees can absorb 10% more greenhouse gases than previously thought, according to a study published Wednesday in the scientific journal Nature.
“It’s a big deal at the global scale,” said Vincent Gauci, the study’s lead author and a professor at the University of Birmingham. As methane can heat the planet more than 28 times faster than CO2 over a century, its removal can have an outsized effect on slowing global warming, Gauci says.
While it was already known that microbes in tree bark eat methane, the study is the first to quantify the volume of atmospheric methane that, on a global scale, trees can remove – somewhere between 24.6 million tons to 49.9 million tons annually. That’s on par with soil, previously thought to be the planet’s only biological sink for the gas.
Methane is responsible for as much as 30% of global warming since the Industrial Revolution and its concentration in the atmosphere has more than doubled over the past two centuries, driven largely by human-related activities. To keep global temperature rises within a livable limit, more than 150 countries have pledged to cut methane emissions by at least 30% below 2020 levels by the end of the decade.
Besides promoting climate-friendly farming practices and switching away from fossil fuel production, the study’s authors say that combating deforestation offers another way for governments to achieve their goal.
The study focuses on so-called upland trees that grow outside of a floodplain. While such trees comprise most of the world’s forests, their interaction with methane hasn’t been studied much. To fill the void, Gauci and his coauthors examined hundreds of trees across geographic locations and climate zones, including tropical forests in the Amazon and Panama, temperate forests in the UK and boreal forest in Sweden.
By strapping gas-measuring equipment to a tree’s trunk, the researchers were able to take real-time measurements of methane fluxes from the tree at multiple heights. Then, with the help of laser scanners, satellite data and computer algorithms, they applied their analysis of individual forests to the global population.
Their findings show that even though some upland trees can emit a small amount of soil-derived methane close to their stem base, the direction of methane fluxes changes farther away from the forest floor.
Perhaps because microbes thrive in warm, wet conditions, the researchers also found that the methane absorption was strongest in the tropical forests.
“It gives us an insight into a new methane sink in the methane budget of the Earth system,” Gauci says. “It also alters our understanding of the climate benefit trees present.”
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