‘‘It’s like taking out food out of your freezer. Leave it on your counter for a few days, and it rots,’’ said University of Florida botany professor Ted Schuur, describing the process by which decaying animal and plant matter in the soil is converted by bacteria into carbon dioxide, methane and other harmful greenhouse gases. The study, published in last week’s issue of the journal Science, concluded that while other global warming researchers are including carbon reserves in the ocean, and in current soils and vegetation on the earth in their calculations, they have inadvertently ignored vast amounts of carbon trapped in permafrost in the north plains of Siberia and central Alaska.

If all the permafrost thawed and was released as heat-trapping carbon dioxide, it could nearly double the 730 billion metric tons of carbon now in the atmosphere, the scientists said. They said what was most surprising was the size and depth of the terrain that they found that could be affected—a piece two-thirds the size of Alaska and an average of 80 ft deep containing roughly 500 billion metric tons of carbon.

‘‘It’s like finding a new continent under the earth,’’ said lead author Sergey Zimov. He said the vast, carbon-rich area had been buried over many millenniums by a unique layer of wind-borne ‘‘loess’’ dust that covered bones of mammoth, bison, saber toothed tiger and abundant grasses they fed on, then froze about 10,000 years ago into permafrost.

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