Alaska is getting wetter. A new study details what that means for the permafrost that underlies roughly 85% of the state, and the consequences for Earth’s global climate.

The study, published today in the journal Nature Publishing Group Climate and atmospheric science, is the first to compare how rain is affecting the melting of permafrost across time, space, and a variety of ecosystems. It shows that increased summer rainfall is degrading permafrost across the state.

While Siberia remains in the headlines of record-setting heat waves and wildfires, Alaska is experiencing the five wettest years in its century-long weather record. Extreme weather at both ends of the spectrum (warm and dry versus cold and wet) is driven by an aspect of climate change called arctic amplification. As the earth warms up, temperatures in the Arctic rise faster than the world average.

While the physical basis for amplification of the Arctic is well understood, less is known how it will affect the permafrost that underlies about a quarter of the northern hemisphere, including most of Alaska. Permafrost blocks about twice as much carbon as is currently in the atmosphere from long-term storage and is compatible with northern infrastructure such as roads and buildings; Therefore, understanding how a changing climate will affect is crucial both for people living in the Arctic and for people living in lower latitudes.

“In our research area, winter has lost nearly three weeks to summer,” says study lead author and Fairbanks resident Thomas A. Douglas, a scientist at the US Army’s Cold Regions Research and Engineering Laboratory. “This, coupled with more rain storms, means that much more rain falls each summer.”

Over the course of five years, the research team took 2,750 measurements of how far the permafrost from the earth’s surface had thawed in late summer in a wide range of settings near Fairbanks, Alaska. The five-year period included two summers with average precipitation, one that was slightly drier than usual, and the upper and third wetter summers on record. Differences in annual precipitation were clearly imprinted on the amount of thawing of permafrost.

More rain led to a deeper thaw at all sites. After the rainiest summer in 2014, permafrost did not freeze to previous levels, even after subsequent summers were drier. Wetlands and disturbed sites, such as trail crossings and clearings, showed the highest amount of snowmelt. The tussock tundra, with its deep soils and tufted grasses, has been found to provide the most protection for the permafrost ecosystem. Although permafrost froze closer to the surface in the tuft tundra, it experienced the largest relative increase in melt depth in response to rain, possibly because water could collect on the flat surface. The forests, especially the spruce forests with thick layers of sphagnum moss, were the most resistant to thawing permafrost. Charlie Koven, a modeler of the Earth system at Lawrence Berkeley National Laboratory, used the field measurements to build a heat balance model that allowed the team to better understand how rain conducted heat to the permafrost soil.

The study demonstrates how land cover types govern the relationships between summer rainfall and permafrost thaw. As Alaska becomes warmer and wetter, vegetation cover is expected to change and wildfires disturb large stretches of the landscape. Those conditions can lead to a feedback loop between more permafrost thaw and wetter summers.

Meanwhile, the rain and the investigation continue. Douglas says: “He was at one of our field sites and it takes hip wading shoes to get to areas that used to be dry or had only deep ankles with water. It’s extremely wet out there. So far this year, almost we’ve doubled precipitation from a typical year. “

“This study adds to the growing body of knowledge about how extreme weather, ranging from hot spells to intense summer rains, can alter fundamental aspects of Arctic ecosystems,” says Merritt Turetsky, Director of the Institute for Arctic and Alpine Research at the University of Colorado Boulder. (INSTAAR) and co-author of the study. “These changes are not occurring gradually over decades or lives; we are seeing how they occur in just months or years.”