Global sea level rise could happen at nearly twice the rate previously projected by the U.N. Intergovernmental Panel on Climate Change, even under the best scenario, according to a new report.

By the end of this century, as some glaciers disappear completely, the Arctic's contribution to global sea level rise will reach at least 19 to 25 centimeters, according to the report by the Arctic Council's Arctic Monitoring Assessment Program (AMAP).

Factoring those numbers into projections about other sources of sea level rise results in a minimum of 52 centimeters of sea level rise by 2100 under a best-case scenario and 74 centimeters under business as usual. "These estimates are almost double the minimum estimates made by the IPCC in 2013," the authors wrote.

The report, called "Snow, Water, Ice and Permafrost in the Arctic 2017," takes a comprehensive look at the changes already underway in the Arctic, as well as what's in store. It was one of a handful of reports examining climate change in the Arctic and its effect on communities there that were released by AMAP in advance of this week's International Conference on Arctic Science and the Arctic Council ministerial in May, when the U.S. will hand off the Council chairmanship to Finland.

The reports synthesize the best peer-reviewed science on various Arctic-related issues, with the hope of informing policy decisions. This work is the bread and butter of the Arctic Council, an eight-country, intergovernmental diplomatic body that commissions and directs work on the Arctic but cannot itself make policy.

The findings are not easy to stomach. The authors also write that the Arctic Ocean could be largely ice-free in summer as early as the late 2030s, and that an influx of warmer water could alter climate as far south as the tropics. But they also include a nugget of hope: There is still time to avert some of the worst impacts.

The trajectory of dramatic climate change in the Arctic is locked in through the middle of the century, when the region is expected to see temperatures at least 4 degrees Celsisus above late 20th century averages. But what happens after that—whether the Arctic's average temperature climbs to 6 degrees C above average or rockets to twice that—depends largely on us, the report says.

If the goals of the Paris agreement are met, end-of-century sea level rise would be reduced by 43 percent—or more than 20 centimeters—compared with a business-as-usual scenario, according to the report. It would also stabilize temperatures over the Arctic Ocean in winter at 5-9 degrees C above the 1986-2005 average.

Though a future Arctic will have far less snow and permafrost, meeting the Paris goals would significantly decrease those losses. The duration of snow cover would stabilize at roughly 10 percent below current values by the end of the century, and permafrost losses would stabilize at 45 percent of present day levels. Under a high-emissions scenario, however, the report found that as much as two-thirds of the permafrost could thaw by 2080, which could cause massive methane releases.

The report includes the work of more than 90 scientists from around the world, and was peer-reviewed by 28 experts. It mostly covers the period of 2011-2015, with some observations from 2016 and early 2017.

One of the challenges in creating a comprehensive report about the Arctic, say some of its authors, is the pace of change there. "The problem is things change so quickly," said Walter Meier, a scientist with the NASA Goddard Space Flight Center Cryospheric Sciences Laboratory who was an author of the report. The report only includes peer-reviewed work, and the peer review process can take a year or more. "The report is almost out of date before it gets published."

That said, this work reflects the most comprehensive look to date at the science of the changing Arctic and its future.

Arctic Communities Feel the Impact

Another set of reports released Monday, called "Adaptation Actions for a Changing Arctic," shifts the focus to the impacts on Arctic communities.

Each of the three reports takes an in-depth look at the challenges facing a different region of the Arctic: the Bering-Chukchi-Beaufort region, the Barents Sea region and the Baffin Bay/Davis Strait region.

Though the challenges, and methods of addressing them differed among regions, the reports' authors found some common themes: Climate change impacts all elements of people's lives in the Arctic, yet their stated concerns are often tied to jobs, food and recognizing some of the economic potential of natural resources.

For instance, in the Barents region, some communities voiced concern about the future of reindeer herding, said Grete Hovelsrud, a social anthropologist from Norway who worked on the report. "The land they use for grazing is being encroached upon by roads, cabins, infrastructure," she said, making it hard to move the herd. Climate change is exacerbating the problem. "The climate is warming, and it may rain in the middle of the winter," she said, causing pastures to ice over. Reindeer can dig through snow to get to grass, but not ice.

In the Alaskan Arctic, loss of sea ice is resulting in larger waves reaching shore, which is increasing coastal erosion and putting communities in peril.

"Many of these communities will be forced to relocate, some in the immediate future, most in the not too distant future," said Larry Hinzman, a professor of Civil and Environmental Engineering at the University of Alaska Fairbanks, who was an author of the report.

And as climate change impacts local ecosystems, it can be harder to hunt and fish for the species these communities rely on—a problem, since many are subsistence hunters. "For these people, serious ecosystem changes immediate impact their ability to obtain food," the report says.

The extensive reports are intended as tools for policymakers.

"They need to start planning for this," said Jon Fuglestad, the deputy executive secretary of AMAP. "I don't think I'll offend anyone by saying that the government structure isn't prepared for meeting this future because it's too fragmented. Adaptation, planning—it takes time. You need to know what you're going to adapt to, and you need to have governance structure that can meet the future changes."