Up to a quarter of the permafrost that lies underneath the surface of Alaska could melt by the end of the century, spewing long-held carbon into the atmosphere and helping accelerate climate change, US government scientists have predicted.

The US Geological Survey used satellite and on-ground data to estimate that 38% of mainland Alaska has permafrost, a band of soil, rock or sediment that is frozen underground for at least two consecutive years. In Fairbanks, Alaska, the soil has been frozen for several thousand years at just 30 to 40cm underground, with only the upper level of soil thawing every summer before freezing again in winter.

But this icy mass is now under threat from warming temperatures. Under scenarios calculated by USGS, 16% to 24% of Alaska’s permafrost will disappear by the end of the century under varying climate change outcomes. The declines are expected to be sharper in the heavily forested central areas of Alaska, rather than the state’s north.

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“Increasing air temperatures have led to widespread thawing and degradation of permafrost, which in turn has affected ecosystems, socioeconomics, and the carbon cycle of high latitudes,” the USGS study states. “Taken together, these results have obvious implications for potential remobilization of frozen soil carbon pools under warmer temperatures.”

The melting of the permafrost would release carbon stored for many years underground, causing the sort of “feedback loop” that has concerned climate scientists: as warming temperatures melt ice in the Arctic region, carbon and methane that has been locked away for thousands of years is being released, thereby fueling more warming and melting.

Facebook Twitter Pinterest A USGS chart maps Alaska’s permafrost. Photograph: US Geological Survey

The USGS has previously said that there would be a “gradual and prolonged” release of greenhouse gases from thawing permafrost but this is the first time the agency has quantified the loss.

There is an estimated 1.4bn to 1.85bn tonnes of organic carbon stored in the Arctic permafrost – around half of all such carbon stored in Earth’s soils. The air temperature in the Arctic has risen twice as fast as the rest of the world. It has gone up 0.6C in the past three decades alone, leading to a pronounced warming underground. Average temperatures in the permafrost have increased by 5.5C since the 1980s.

The level of Alaskan permafrost melting will depend on the severity of climate change and doesn’t factor in possible future disturbances such as wildfires. But it complicates the effort needed to keep global temperatures below a 2C increase on pre-industrial times. Greenhouse gas reductions promised by nations currently locked in climate talks in Paris would result in warming of at least 2.7C, a scenario that doesn’t factor in the consequences of feedback loops.

“A warming climate is affecting the Arctic in the most complex ways,” said Virginia Burkett, USGS associate director for climate and land use change.

“Understanding the current distribution of permafrost and estimating where it is likely to disappear are key factors in predicting the future responses of northern ecosystems to climate change.”