Duration of continuous snow cover steadily declining, with its onset in the fall and melting away in spring revealing the biggest shifts relative to what was once normal.

The Arctic is facing a complex and ever-widening cascade of environmental changes that will increasingly challenge northern communities and affect people around the globe.

That is the takeaway from this year’s Arctic Report Card, an annual compilation of observations and trends by the U.S. National Oceanic and Atmospheric Administration, with contributions from Canada and other circumpolar countries.

Now, 15 years since the first report card was issued, scientists say those trends are abundantly clear in a part of the world that is warming two to three times faster than the global average owing to climate change.

According to the latest report card, released Tuesday, the transformation of the Arctic is both “rapid and pronounced.” It includes long-observed effects such as reductions in sea ice and snow cover, retreating glaciers and thawing permafrost. Other, more recently observed phenomena range from a proliferation of woody shrubs and beaver dams across the tundra to a Bering Strait awash in marine garbage owing to increased shipping traffic.

“As the Arctic transforms, science in some cases is running to keep up,” the authors write.

More than 100 researchers in 12 countries contributed to the report card, which provides yearly assessments of the Arctic environment in intervals that cover one summer season to the next.

Looking back over the 2020-21 interval, the report card notes that the year was the seventh-warmest overall for the region, with the period of October to December, 2020, ranking as the warmest Arctic autumn since recordkeeping began in 1900. The volume of postwinter sea ice on the Arctic Ocean was also the lowest in a decade, with multiyear ice reaching its second-lowest extent.

The report card also references recent studies that show the rate of acidification of the Arctic Ocean owing to uptake of carbon dioxide is among the fastest in the world. Higher acidity weakens the shells of marine mollusks, including the sea snails, clams and mussels that are important food sources for other species.

Another marked change is the duration of continuous snow cover, which has steadily declined across the Arctic and last year was the shortest ever for Siberia.

While the ground is always covered in snow during the Arctic winter, particularly in those areas that see little or no sunlight at that time of year, it is the onset of snow in the fall and its melting away in the spring that reveal the biggest shifts relative to what was normal a few decades ago.

“It’s not a subtle thing, like a day or two,” said Chris Derksen, a research scientist with Environment and Climate Change Canada who contributed to this year’s report card. “We’re seeing changes on the order of weeks.”

As one example, last winter the community of Inuvik in the Northwest Territories experienced 30 fewer days of snow cover between February and July than it did in 2001. Lawrence Mudryk, an Environment and Climate Change Canada researcher who led the snow cover section of the report card, said spring decreases in snow cover have been particularly strong across the western portion of the Canadian Arctic in the past two decades. And while snow cover can vary from year to year with large regional differences, the longer-term pattern is similar across much of the Arctic.

Such differences can set in motion a host of other effects, Dr. Derkson said. For example, an earlier spring thaw means water can seep into the ground and accelerate the thinning of permafrost. It also changes the timing and amount of freshwater runoff from rivers that flow into the Arctic Ocean, which further alters the cycles of coastal marine life. In some areas, the early disappearance of snow cover also correlates with increased wildfire activity later in the summer.

On a global scale, the reduction of snow and sea ice across the Arctic means more sunlight is absorbed by both land and sea rather than reflected back into space. Climate models have shown this contributes to a positive feedback loop that can warm the planet more rapidly and amplify the effects of climate change, including severe weather events, at mid-latitudes.

Another change linked to the decrease in snow cover has been dubbed the “shrubification” of the Arctic tundra. It describes the shift in many areas from grasses and other low-lying plants to taller, bushier species that can take advantage of a longer growing season.

Howard Epstein, a vegetation ecologist at the University of Virginia who has contributed to every report card since the annual assessment was launched, said increased plant productivity in the Arctic has some positive climate effects through the increased uptake of carbon dioxide. However, he said, the change in vegetation is also a contributor to the disappearance of permafrost, which in turn contributes to the release of stored soil carbon.

“The general thought is that we’re more likely to see more carbon dioxide put into the atmosphere than taken out of the atmosphere due to the increase in vegetation,” Dr. Epstein said.

Maribeth Murray, a University of Calgary professor and director of the Arctic Institute of North America, said she was struck by a description in this year’s report card of beaver dams and their growing impact in Alaska – another sign of southern ecosystems spreading northward and altering the Arctic landscape.

Dr. Murray, who was not a co-author on the report, said it shows what northern communities are facing in terms of threats to food security, transportation and infrastructure – all of which will be harder to maintain on a landscape that is no longer frozen.

“Communities are already responding to the best of their ability … but the changes are happening faster than we think, and we don’t have the regulatory frameworks or the political will to help people manage and adapt,” she said.

The Globe and Mail, December 14, 2021