Global warming will cause ecosystems to produce more methane than was first predicted.

New research suggests that as Earth warms, natural ecosystems, such as freshwater, will release more methane than expected based on predictions based only on temperature increases.

The study, published today in Climate change, attributes this difference to changes in the balance of microbial communities within ecosystems that regulate methane emissions.

The production and removal of methane from ecosystems is regulated by two types of microorganisms, methanogens, which naturally produce methane, and methanotrophs that remove methane by converting it to carbon dioxide. Previous research has suggested that these two natural processes show different temperature sensitivities and therefore could be affected differently by global warming.

Research led by Queen Mary University of London and the University of Warwick studied the impact of global warming on freshwater microbial communities and methane emissions by looking at the effect of experimental warming of artificial ponds for 11 years. They found that warming produced a disproportionate increase in methane production over methane removal, resulting in an increase in methane emissions that exceeded temperature-based predictions.

Professor Mark Trimmer, professor of biogeochemistry at Queen Mary, said: “Our observations show that the increase in methane emissions we see is beyond what could be predicted based on a simple physiological response to the increase in temperature. Long-term warming also changes the balance in the methane-related microbial community within freshwater ecosystems so that they produce more methane while proportionally less is oxidized to carbon dioxide. As methane is a much more greenhouse gas more potent than carbon dioxide, these effects together increase the global warming potential of carbon gases released from these ecosystems. “

The experimental observations were supported by a meta-analysis of available data on methane emissions collected from wetlands, forests and grasslands worldwide, which showed that naturally warmer ecosystems also produce disproportionately more methane.

Professor Trimmer said: “Our findings fit what we see in the real world for a wider variety of ecosystems. Together, these results suggest that as Earth’s temperatures rise through global warming, natural ecosystems they will continually release more methane into the atmosphere. “

Dr. Kevin Purdy, associate professor of microbial ecology at Warwick, added: “Our studies have led to a better understanding of how global warming can affect methane emissions from freshwater. This means that future predictions of emissions methane must take into account how ecosystems and their resident microbial communities will change as the planet warms. “

Methane is a powerful greenhouse gas with about 28 times the global warming potential of carbon dioxide over a period of 100 years. More than 40 percent of methane is released from freshwater such as wetlands, lakes, and rivers, making them a major contributor to global methane emissions *.