Scientists have found an increase in global wetland methane emissions in recent years, according to a study published in the journal Nature Climate Change. 

Over the past 20 years, wetland methane emissions have increased by an average of 1.3 to 1.4 million tonnes per year. The concentration of methane in the atmosphere has been increasing rapidly since 2007, hitting record highs for two consecutive years in 2020 and 2021. The increasing trend in wetland methane emissions is higher than previous estimates of an average increase of 0.9 million tonnes per year, the findings show. 

The study indicates that these emissions may play a bigger role in the future.

Observational data reflects that the methane carbon 13 stable isotope content in the global atmosphere is showing a continuous downward trend, which means that natural emission sources such as wetlands may be the dominant factor in the composition of atmospheric methane sources.

Methane is a powerful greenhouse gas having more than 80 times the warming power of carbon dioxide over the first 20 years after it reaches the atmosphere.

Wetlands cover about 6 percent of the Earth's land surface and are one of the largest natural sources of methane. 

As the global temperature rises, the activity of methane-producing microorganisms in wetland ecosystems also increases, releasing more methane, according to Zhang Zhen, co-author of the study. 

This phenomenon, dubbed "wetland methane feedback," is an important natural feedback process in Earth-system science and has a significant impact on climate change, Zhang said. 

Field survey data shows that South America is the largest contributor to global wetland methane emissions, while satellite data suggests that South and Southeast Asia are also responsible for high emissions, the study says, calling for sustained monitoring of global wetland methane fluxes to document emerging trends, variability and underlying drivers.

Wetlands' reaction to temperature rise

A separate study, also published in the journal Nature Climate Change recently, found if the global temperature rises by 1.5 to 2 degrees Celsius, the function of wetlands as greenhouse gases sinks will weaken by about 57 percent, diminishing their role in mitigating climate change.

Researchers from the Institute of Atmospheric Physics under the Chinese Academy of Sciences integrated data from warming simulations conducted at 167 independent natural wetland sites between 1990 and 2022. They studied the response of the net exchange of three greenhouse gases to warming.

Wetlands have a high potential for mitigating climate change because of their large carbon stocks. However, whether and where wetlands will act as greenhouse gas sinks or sources under warming is uncertain.

In wetlands dominated by vascular plants such as shrubs and grasses, warming has increased the carbon dioxide sink. In wetlands dominated by mosses, lichens and other cryptic plants, however, the warming has raised carbon dioxide emissions.

The warming has also increased the net emission of methane and nitrous oxide of the wetlands regardless of their dominant plants, according to the study.

"The Paris Agreement aims at keeping global warming below 2 degrees Celsius above pre-industrial levels and striving for a lower limit of 1.5 degrees Celsius. In this context, our study on the change of wetlands as greenhouse-gas sinks will help to better cope with global climate change," said Xu Xiyan, one of the researchers. 

(With input from Xinhua)