The rate at which the Earth's permafrost is melting suggests that the tipping point would occur within the next 20 years, warns study. This will mark the point at which the Arctic turns from being a net 'sink' for carbon dioxide into an overall source that will accelerate global warming.
According to the researchers, billions of tons of frozen leaves and roots that have lain undisturbed for thousands of years in the permanently frozen ground of the northern hemisphere are thawing out, with potentially catastrophic implications for climate change, reports the Independent.
The study also found that by 2200 about two-thirds of the Earth's permafrost will have melted, releasing an estimated 190 billion tons of carbon dioxide and methane into the air - about half of all the fossil fuel emissions of greenhouse gases since the start of the industrial revolution.
"As the Arctic warms up, this frozen carbon will thaw out, allowing microbial decay to resume and releasing carbon into the atmosphere," said Kevin Schaefer of the US National Snow and Ice Data Centre in Boulder, Colorado.
"Our research shows that the release of carbon from permafrost will result in an irreversible climate tipping point in only 20 years... Once the frozen carbon thaws out and decays, there is no way to put it back into the permafrost," Dr Schaefer said.
"There are two important messages from this study. The first is that the melting permafrost can release huge amounts of carbon and, secondly, the process is irreversible on a human timescale and will affect our targets for reducing fossil fuel emissions," he added.