The Arctic is experiencing some of the most rapid and severe warming on the planet, according to a new, eight-nation report — the most comprehensive assessment of Earth’s fragile northern cap to date.

The report, a four-year effort involving hundreds of scientists, describes vast areas of melting ice, declining species and fading indigenous cultures.

“It’s affecting people up there now,” said Robert Corell, the American oceanographer who led the project. “And there are very serious consequences for people on the rest of the planet.”

The report states that climate change is accelerating sharply, spurred by human production of greenhouse gases, which have increased in the atmosphere by nearly 30 percent since the Industrial Revolution.

The 140-page report, released Monday, chronicles the many changes that have resulted as the Arctic has warmed in recent decades. Average temperatures there have risen nearly 2 degrees Fahrenheit in the past century — twice the global average — while winter temperatures have risen nearly 4 degrees.

Parts of Alaska and Russia have seen average winter temperatures rise 11 degrees since the 1970s; they are the highest in 400 years, according to the report. The amount of ocean covered by ice over the past three years has been the lowest ever recorded.

Among the most obvious changes are the melting of the massive Greenland ice cap and other Arctic glaciers and the decimation of northern forests by foreign insect invasions. Some coastal villages are jeopardized by erosion and rising seawater.

Many environmental groups hailed the Arctic report and said it was an urgent call for the United States, which has been reluctant to agree to international limits on greenhouse gas production, to join the efforts of other nations.

Large sections of the report deal with problems faced by indigenous Arctic people, who tell of hunters falling through melting sea ice, declining reindeer herds and difficulty traveling in roadless regions with no snow for their snowmobiles and sleds.

In more developed areas of the Arctic, buildings, pipelines, runways and roads are beginning to crumble as the permafrost beneath them thaws and becomes less stable.

Although the problems are immediate to many of the Arctic’s 4 million residents, the changes will affect the rest of the world as well, scientists said. Melting sea ice and ice sheets raise the sea level, which could affect low-lying cities in Florida and Louisiana, for instance. The fresh water flowing into the ocean could alter the marine circulation patterns that help moderate the global climate.

Melting ice exposes darker ground, which absorbs more sunlight and leads to greater warming, which in turn melts even more snow. This means that the reduction of snow and ice cover in the Arctic is likely to accelerate warming across the Earth, according to the researchers.