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But to the scientists from Woods Hole Research Center who have come here to study the effects of climate change, the most urgent is the fate of permafrost, the always-frozen ground that underlies much of the state.

Starting just a few feet below the surface and extending tens or even hundreds of feet down, it contains vast amounts of carbon in organic matter — plants that took carbon dioxide from the atmosphere centuries ago, died and froze before they could decompose. Worldwide, permafrost is thought to contain about twice as much carbon as is currently in the atmosphere.

Once this ancient organic material thaws, microbes convert some of it to carbon dioxide and methane, which can flow into the atmosphere and cause even more warming. Scientists have estimated that the process of permafrost thawing could contribute as much as 1.7 degrees Fahrenheit to global warming over the next several centuries, independent of what society does to reduce emissions from burning fossil fuels and other activities.

In Alaska, nowhere is permafrost more vulnerable than here, 350 miles south of the Arctic Circle, in a vast, largely treeless landscape formed from sediment brought down by two of the state’s biggest rivers, the Yukon and the Kuskokwim. Temperatures three feet down into the frozen ground are less than half a degree below freezing. This area could lose much of its permafrost by midcentury.

That, said Max Holmes, senior scientist and deputy director of the research center, “has all kinds of consequences both locally for this region, for the animals and the people who live here, as well as globally.”

“It’s sobering to think of this magnificent landscape and how fundamentally it can change over a relatively short time period,” he added.

But on this wide, flat tundra, it takes a practiced eye to see how Alaska is thawing from below.

At one of the countless small lakes that pepper the region, chunks of shoreline that include what had been permafrost have calved off toward the water.

Nearby, across a spongy bed of mosses and lichens, a small boggy depression most likely formed when the ice in the top layers of the permafrost below it melted to water……….

Beyond the local effects on plant and animal life, the landscape changes can have an important climate change impact, by altering the mix of carbon dioxide and methane that is emitted. Although methane does not persist in the atmosphere for as long as carbon dioxide, it has a far greater heat-trapping ability and can contribute to more rapid warming.

So the researchers devote much of their time to studying the flow of water and the carbon and nutrients it contains…….

Estimates vary on how much carbon is currently released from thawing permafrost worldwide, but by one calculation emissions over the rest of the century could average about 1.5 billion tons a year, or about the same as current annual emissions from fossil-fuel burning in the United States.

Already, thawing permafrost and warmer temperatures are being blamed for rising carbon emissions in the Alaskan tundra, both here and farther north. In a study earlier this year, researchers found that bacterial decomposition of thawed permafrost, as well as carbon dioxide produced by living vegetation, continues later into the fall because freezing of the surface is delayed.

The rise in emissions has been so significant, the researchers found, that Alaska may be shifting from a sink, or storehouse, of carbon, to a net source.

Dr. Holmes said that shift was not surprising given the climate trend, and he would expect that sub-Arctic parts of Siberia, Canada and other areas with permafrost may be undergoing similar changes.

“There’s a massive amount of carbon that’s in the ground, that’s built up slowly over thousands and thousands of years,” he said.

“It’s been in a freezer, and that freezer is now turning into a refrigerator.” https://www.nytimes.com/interactive/2017/08/23/climate/alaska-permafrost-thawing.html