Contrary to earlier assumptions that permafrost was as barren as polar desert, samples taken by the research team found 10 to 30 times as much carbon as in deep soils elsewhere. Schuur said most previous studies only looked at samples about 3 ft deep.

Another recent study estimated that about 10 ft of permafrost will melt in the 21st century, still meaning billions of tons could be released if global warming is not slowed or halted. The Russian-American research team, funded by the National Science Foundation in the US, also found that carbon stored over tens of thousands of years could bubble up from thawed soil in as little as 100 years.

‘‘Because this is a very sensitive sort of climate, if the permafrost begins to melt, billions of gallons of greenhouse gases will be released from these ancient soils,’’ said Zimov. The authors said they hoped the findings would spur quicker reductions of human caused greenhouse gas emissions from car tail pipes and other fuel releases.

‘‘It’s not hopeless,’’ said Schuur. ‘‘We’re just at the beginning of this cycle, so we can, through the controlling of emissions, have a hope of slowing down this rate of global warming that would slow the melt of the permafrost.’’

Janet Wilson