Dr Richard Pancost from the University of Bristol and colleagues, have shown in their study in Nature that carbon isotope values of hopanoids - compounds made by bacteria - suddenly decrease in a manner that can only be explained by switching to a diet of methane.
This possibly caused methane emissions to increase 55 million years ago, he said.
As part of their study, the team from Bristol University, Royal Holloway and other institutions analysed the geochemical composition of sediments taken from the Cobham Lignite wetland in southeast England, revealed when the Channel Tunnel rail link cut through it.
"Fifty-five million years ago, a massive release of carbon into the atmosphere caused significant global warming. It is likely that this warming and associated climate change caused a change in environmental conditions that brought about increased methane emissions. This in turn, may reflect an increase in methane production and subsequent release from the terrestrial biosphere," said Dr Pancost.
He said methane being a very powerful greenhouse gas could have caused further warming if the processes occurring at Cobham were widespread.
It could also amplify the climate change at that time, he said.
Professor Andrew Scott of Royal Holloway, however, said this section could not be used as an "exact model for interpreting future global warming as the climate 55 million years ago was very much warmer than that of today."
Dr Pancost nevertheless added, "Although we must be careful not to over interpret the data obtained from a single site, this does provide insight into how some ecosystems could respond to rapid warming-induced changes in climate, and therefore, how they could respond to warming in the future."
"In such a scenario, not only will warming occur due to the carbon pumped into the atmosphere by our burning of oil and coal, but also due to the biological response of some ecosystems," he said.