A jackhammer is needed to dig deeper into the permafrost.

The summer tundra.

In Shishmaref, Alaska, melting permafrost has contributed to major erosion, forcing residents to consider moving the entire village to a new location.

Melting permafrost from above.

If you want to dig a ditch in the Arctic, you’d better bring more than a shovel. Even at the height of summer, you may only be able to dig down a foot or two before you hit solid, frozen soil known as permafrost. Permafrost is found in places where the average annual temperature is below about 23°F (- 5° C), including most of the Arctic and all of Antarctica.

Land with underlying permafrost is called tundra. The arctic tundra is stark and treeless. Roots can’t penetrate the frozen soil, so only moss, lichen, and low shrubs can grow there. In summer, the topmost layer of the permafrost melts, leaving behind soggy ground, marshes, bogs, and lakes.

Buildings constructed on permafrost have a notorious tendency to sink, crumble, or tilt like the Leaning Tower of Pisa. That’s because heat and pressure from overlying structures can cause the permafrost just under the structure to melt, turning formerly firm soil into mush.

In recent years, however, permafrost has been melting en masse, thanks to increases in global average temperatures. The zones where permafrost can be found year-round are creeping northward, and permafrost coverage, currently 20 percent of the earth’s land surface, is predicted to shrink drastically in coming years.

A mass-melting of permafrost would contribute significantly to rising sea levels. It might also accelerate global warming by releasing greenhouse gases into the air. Rich in organic material, the soil in the Arctic tundra will begin to decay if it thaws. As it breaks down, it will release large amounts of methane and carbon dioxide—two greenhouse gases—into the atmosphere. Thawing permafrost could thereby result in a positive feedback loop in which thawing causes faster warming, resulting in more thawing.

Climate change is a topic of worldwide concern, but it’s of particular concern at the poles. That’s because the impacts of global warming are felt first and most severely at higher latitudes. Given this, it’s not surprising that the poles are also where much of the research concerning global climate change is taking place—or that climate change was the central focus of the 2007–2008 International Polar Year.

Melting iceberg, Antarctica.

The Arctic has experienced warming at twice the rate of the rest of the world. Winter temperatures have increased by up to 8° F (4° C). Snow and sea ice coverage have shrunk by 10 percent and 20 percent respectively in the last 30 years. The summer of 2007 saw an unprecedented mass-melting of one million additional square miles of sea ice, an area larger than Texas and Alaska combined. Glaciers are in retreat throughout the Arctic, and the ice sheets that cover Greenland and Antarctica are melting at record rates.

Climate change hits the poles hardest for a variety of reasons: Melting of highly reflective sea ice means increased absorption of the sun’s rays by the dark ocean. A shallower atmosphere at the poles means that less heat is needed to increase air temperatures near the surface. And in contrast to equatorial areas, cooling by evaporation is minimal at the chilly poles.

Collecting an ice core. Look closely to see the thousands of ancient air bubbles trapped inside the ice.

To understand how our climate is changing, scientists must delve back in time. Drilling cores of ancient ice and sediment lets researchers chart past changes in climate over millions of years, using trapped air bubbles, residues of living things, and other environmental clues.

Researchers also monitor current atmospheric and environmental conditions. They track patterns in populations of wildlife from krill to whales, measure the thickness of sea ice in the ocean and the extent of glaciers on land, and detect changing concentrations of greenhouse gases such as carbon dioxide and methane in the air.

Data from the past and present helps researchers develop computer models of our climate, models that we can use to envision likely future scenarios. An important aspect of this study is understanding feedback effects: How will temperature-driven changes in the Arctic—such as melting sea ice or thawing permafrost—affect future climate change?

A house in Shishmaref, Alaska, undermined by erosion, finally falls over. As permafrost melts and warmer temperatures keep sea ice from forming until late in the year, erosion has increased, forcing Shishmaref residents to consider relocating the entire village.