TOOLIK FIELD STATION, Alaska – Beyond the Arctic Circle, teams of scientists measure widening slumps as ice melts beneath the tundra. They scuff through tussocks blackened by unexpected fires, and search for fish in drought-depleted streams.

The researchers are taking the pulse of a warming Earth in a landscape supremely adapted to cold, one that may be an early-warning zone for lands far south.

"It's not just an Alaska thing," said Syndonia "Donie" Bret-Harte, associate science director at Toolik Field Station. "What goes on here has a potential to influence the rest of the lower 48 (states).

"The Arctic acts as North America's air conditioner," added Bret-Harte, who did postdoctoral work at UC Davis in the early 1990s.

Potentially affecting the function of that air conditioner are two forces: rot and reflection.

Buried in snow and darkness for much of the year, the Arctic resists decay. That makes it a vast storehouse of carbon, holding one-sixth of the planet's soil carbon. As the land warms, a microbial feeding frenzy could send more carbon dioxide into the air.

Beyond that, as sea ice melts and snow cover dwindles, both expose darker, less reflective surfaces that can absorb heat like asphalt baking in the sun, further accelerating warming.

When large air systems move across warmer land and sea, weather patterns can change, shifting regions of drought and rainfall thousands of miles away.

Monitoring how climate has changed so far, and teasing out complexities of what might happen next, are among the priorities at Toolik Field Station, nearly 400 miles north of Fairbanks.

It is "one of the premier locations in the Arctic" for field research, known for the "robust science" it has produced, said Hank Loescher, staff scientist for the National Ecological Observatory Network in Boulder, Colo.

For researchers who have spent much of their careers working at Toolik each summer, the localized changes are striking.

What they're finding, so far, is that the frozen earth beneath their feet is gradually warming.

Bore holes drilled deep into the permafrost are 3 to 5 degrees Fahrenheit warmer than they were in the late 1970s. Sea ice is melting so much faster than predicted that, at a recent conference Bret-Harte attended, researchers were taking bets on when it would disappear entirely. Average air temperatures are rising more rapidly than in temperate or tropical zones. Spring arrives earlier, and fall later.

"When someone tells you it's going to be a little warmer and a little drier, you don't think much is going to happen. But in reality, that's a big, life-changing event" for some plants and animals, said Linda Deegan, who studies streams around Toolik.

It only takes a small decline in some Arctic streams to kill virtually all the fish, because a diminished flow can cut off their route to deep lakes where they find shelter in winter.

"For the first 15 years I was here, we never saw a drought. In the last 10 years, there have been three," said Deegan, a senior scientist at the Marine Biological Laboratory at Woods Hole, Mass. She recalls the last drought as "just catastrophic" for fish.

Bret-Harte worries that the ankle-high tundra plants which carpet this frigid area could be confused into blooming a second time in fall, squandering their chance to produce fruit the following year. Among those already blooming out of turn are important food plants such as the lowbush cranberry and a variety of blueberry.

Some researchers, though, are resigned to changes they see as inevitable, and thus more careful about projections of how warming might play out in the lower 48.

Vladimir Romanovsky, a University of Alaska permafrost specialist who has been tracking temperatures in bore holes, can't understand why today's culture seems to believe every species must to be saved.

If polar bears interbreed with the grizzlies, "or even if they disappear, it's bad, of course," Romanovsky said with a little shrug. "But why do we have to preserve them? Species were always disappearing. … In a warmer planet, there will be some winners and losers, like always."

Call The Bee's Carrie Peyton Dahlberg, (916) 321-1086. She was among 10 journalists on an Arctic tour sponsored by the Woods Hole Oceanographic Institution's Marine Biological Laboratory and funded by the National Science Foundation.