Fairbanks, Alaska - What geologists call permafrost was once defined as permanently frozen ground, covering nearly a quarter of the earth's land area.

But the changing northern climate has forced a redefinition. Permafrost is now "perennially frozen ground" says scientist Vladimir Romanovsky of the University of Alaska Fairbanks' Geophysical Institute.

"It's warming up," says Romanovsky, "even the deepest permafrost is several degrees warmer than it was 30 years ago".

Permafrost is found across the top of the Northern Hemisphere, especially in Alaska, Arctic Canada and Siberia in Russia. Originally from Moscow, Romanovsky has travelled over much of those regions, measuring temperatures and observing the effects of melting permafrost.

"Some of this [permafrost] is almost two million years old. Most of it is 100,000 years or less," he says, "and it's thawing, generations of ice frozen into the ground".

Flipping through a PowerPoint presentation he gives to his students and fellow scientists alike, Romanovsky shows photographs that demonstrate why melting permafrost matters.

He shows photographs of buildings that have collapsed in Siberia, and Alaskan roads and villages with sagging houses and roads ripped apart when the ice melted beneath their foundations.

Without hesitation, he blames climate change.

"Anything that happens to the climate, it's reflected in the permafrost," he says. "Warmer temperatures, less permafrost, it's simple."

'More warming'

Even if society agreed to address climate change immediately, the vast areas covered by permafrost would still face what scientists call "positive feedback". Fossilised organic material - mostly carbon - now encased in permafrost would be released into the environment, in effect greenhouse gas from the ground. This is especially true for north-eastern Siberia, essentially a huge frozen swamp.

"We estimate that there's twice as much carbon in the permafrost layers as in the atmosphere now, so we're looking at tripling the carbon dioxide. And that means more warming. It's a cycle," Romanovsky says.

Climate change has profound geological effects [Jet Belgraver/Al Jazeera]

Of course the global climate has warmed and cooled in cycles throughout geological time. Studying how this happened in the past, and the consequences, might help us cope with what's coming.

At a unique underground laboratory just outside Fairbanks, the US army has converted a Cold-War-era military research facility into a complex to examine 40,000 years of permafrost formation and destruction.

Two tunnels dug into a hillside stretch through layer after layer of ice, frozen gravel and fossils.

Engineer Kevin Bjella - who works for the US army's Cold Regions Research and Engineering Laboratory, (CRREL) - has a surprising warning for visitors to Permafrost Research Facility, as the tunnels are known.

"Mind the smell," he says, "some people find it overwhelming".

Teasing out a picture

Walking along the dimly lit passage behind the entrance, the aroma is indeed powerful, a cross between a farmyard in the summer and the pungent whiff of a brewery.

"It's the organic material," he says, pointing to grass, twigs and other fragments protruding from the walls and ceiling.

There are also bones, from now-extinct bison and mastodon. This part of Alaska was once a fertile steppe with plenty of food for plant-eating mammals. When climates cooled and glaciers rolled in, all organic life was swept away and frozen into the ground.

The Ice Age that scientists study in the tunnels, started 40,000 years ago, says Bjella, and continued up to the start of the current glacial period, 12,000 years ago. It's a journey through time, through the permafrost layers, in search of explanations for climate change that may be relevant today."It's about teasing information from the dirt, from the organic material, from the ice itself," Bjella says, "and seeing what the temperatures were, when they changed, and what happened.

"If we could share that with climate modellers working today, we'd be more ready for the challenges ahead."

The walls of the tunnels tell numerous stories. Here, a layer of dirt between slabs of ice shows a period when a cold climate warmed up, permafrost thawed and then formed again on top of the earth and the dead, geological era plants.

Irregular patterns known as ice wedges are full of frozen water that once flowed on the surface and itself sped up the thawing of local permafrost.

Finally, a layer of coarse gravel at the bottom of deepest shaft was left behind after miners scraped up all the loose rocks and sieved them for gold.

Bjella says scientists from many disciplines work in the tunnels, from palaeontologists to DNA specialists, "teasing out" the picture of a relatively recent - and relevant - past.

"We're not trying to scare anyone here," he says, "It's not about telling everyone climate change will be as disastrous so they should stop using gas. It's about being ready for what's coming, preparing engineering and infrastructure solutions for the people that live here."

For many communities in Alaska, the permafrost melt is already changing their lives.

Think of those pictures in Vladimir Romanovsky's PowerPoint presentation.

In some coastal areas, whole villages have to be moved and local infrastructure replaced, as erosion and sinking ground make their surroundings dangerous and uninhabitable.

Higher ground

For Jack Hebert of the Cold Climate Housing Research Center, the answer lies in both the past and the present.

"People in rural Alaska lived successfully and sustainably for up to 12,000 years," he says. "In less than a century that has all changed.

"To help those communities, we listen to them and we emphasise indigenous wisdom and 21st century technology."

It all starts with the foundation, he added - and with knowing how stable local permafrost may be.

Houses can be set on stilts so their warmth doesn't speed melting. Or a so-called "thermal raft" can be built, essentially a solid platform that insulates the ground from the dwelling. In some areas, homes will be placed on skids so they can be moved to higher, safer ground if drastic reductions in permafrost take place.

"Shelter is life or death here," Hebert says. "It has to protect us, but not isolate us from the environment or community. That's what we're trying to do."

Even as the climate warms, the very ground beneath their feet is changing.