They used to ride snowmobiles in June in Russkoye Ustye, a Siberian village by the Arctic Ocean coast.

Last week, the temperature in the area hit 88 degrees.

"Nature is taking its revenge on us, probably," Sergei Portnyagin, the village head, said by telephone. "We’ve been too bloody in how we’ve treated it."

The climate has been warming rapidly in the Arctic for years, but even by those standards, a heat wave roasting northern Siberia for the past few weeks has been shocking.

Wildfires are spreading. The fishing is meager, the mosquitoes ravenous. People are nailing their windows shut with foil and blankets, seeking refuge from the midnight sun.

The town of Verkhoyansk, more than 400 miles farther north than Anchorage, Alaska, topped 100 degrees Fahrenheit last Saturday, possibly the hottest temperature ever recorded above the Arctic Circle.

Verkhoyansk had been best known as a place of exile in czarist Russia and for sharing the Northern Hemisphere’s cold temperature record — 90 degrees below zero Fahrenheit, set in 1892.

Even before the current heat wave, climate change has been transforming life in Russia’s northern reaches, with global implications.

"Very strange things are happening here," said Roman Desyatkin, a scientist based in the Siberian city of Yakutsk who studies perhaps the most far-reaching consequence of the region’s warming climate — the thawing of its frozen ground. "Our plants, our animals and our people are not used to such great heat."

The frozen ground, or permafrost, lies just below the surface across much of Russia — as well as swaths of Alaska, Canada, and Scandinavia. In some areas, including parts of northeastern Siberia, the permafrost contains large chunks of ice.

With every hot Arctic summer, more of it thaws, flooding pastures, twisting roads, destabilizing buildings and eroding riverbanks.

The thawing permafrost has global consequences because it results in the release of greenhouse gases from the decomposition of organic material that had long been frozen. A group of scientists convened by the United Nations said last year that the process could unleash as much as 240 billion tons of carbon by 2100, potentially accelerating climate change.

For Russia, the warmer climate brings some benefits. Officials hope the receding sea ice will spur greater trade by ships crossing between Asia and Europe via the Arctic Ocean, and will further ease access to oil and gas under the sea.

But it comes at a cost: Addressing the damage to Russian buildings and infrastructure caused by thawing permafrost alone could total more than $100 billion by 2050, scientists estimated last year.

This year’s heat has already contributed to an environmental disaster, Russian officials say. A fuel tank near the isolated Arctic mining city of Norilsk burst in late May after sinking into permafrost that had stood firm for years but gave way during a warm spring, officials said. It released about 150,000 barrels of diesel into a river.

The Arctic has been heating more than twice as fast as the rest of the world, and annual temperatures in the region from 2016 to 2019 were the highest on record. But this year may be even hotter.

Temperatures in Siberia were 18.5 degrees Fahrenheit above average in May, the World Meteorological Organization said, "driving the warmest May on record for the entire Northern hemisphere and indeed the globe."

Above the Arctic Circle, there has been no escaping the heat because the sun shines around the clock.

In the town of Srednekolymsk, Mayor Nikolai Chukrov nailed a blanket to the inside wooden frame of one of his windows to help his two layers of curtains keep out the sunlight. The store had run out of fans, so he borrowed a red-and-white, Soviet-made model from his relatives.

The heat, he said, is a boon to the children playing in the river and to the residents benefiting from a longer growing season for their vegetables. But it also seems to bring even greater swarms of mosquitoes.

"It’s scary, even," Mr. Chukrov said.

The acrid smoke from wildfires has already drifted over Srednekolymsk and other Siberian villages. Last year’s Siberian fires, accelerated by the dry heat, were the worst in recent memory, consuming more than 38,000 square miles — roughly the size of Kentucky.

This year is off to an even worse start. About 7,900 square miles of Siberian territory had burned so far this year as of Thursday, compared to a total of 6,800 square miles as of the same date a year ago, according to official data.

"Only the rain can put out these fires," Mr. Chukrov said. "This year, we have no rain."

The tundra is also on fire outside Russkoye Ustye, said the village head, Mr. Portnyagin. The settlement is one of Russia’s best-known outposts because ethnic Russians first settled there, near the Arctic Ocean coast, in the 16th or 17th century.

The village’s older buildings, however, have all collapsed into the river over the last three decades as a result of the erosion brought on by the thawing permafrost, he said. Other changes appeared more recently: In the past five years, he has started noticing bird species that had never before flown that far north.

For the second straight year, Mr. Portnyagin said, the area around the village was no longer passable by snowmobile in June. Tundra flowers that normally bloom in mid- to late July are already in blossom.

The village residents, unused to the heat, are developing headaches and skin problems because of it, Mr. Portnyagin said.

The normally plentiful fish have descended to the depths because of the warm water, he said, so "the fishermen are suffering."

Three hundred miles to the east, where the Kolyma River flows into the Arctic Ocean, Indigenous reindeer herders have also seen their seasonally regimented way of life scrambled by climate change. The river ice broke up earlier than usual this year, and migratory birds arrived earlier than usual. Unfamiliar plants are growing in the tundra.

"Everything is changing somehow," said Pyotr Kaurgin, the leader of an Indigenous community in the area. "The old men used to predict what the summer would be like and what the winter would be like. We no longer can say for sure."