The fringes of the coldest continent are starting to feel the heat, with the northern Antarctic Peninsula warming faster than virtually any place on Earth. These rapidly rising temperatures represent the first breach in the enormous frozen dome that holds 90 percent of the world’s ice.

In 1978, when few researchers were paying attention to global warming, a prominent geologist at Ohio State University was already focused on the prospect of fossil fuel emissions trapping heat in the Earth’s atmosphere. His name was John H. Mercer, and when he contemplated what might be in store for the planet, his thoughts naturally gravitated to the biggest chunk of ice on Earth — Antarctica.

“If present trends in fossil fuel consumption continue...” he wrote inNature, “a critical level of warmth will have been passed in high southern latitudes 50 years from now, and deglaciation of West Antarctica will be imminent or in progress... One of the warning signs that a dangerous warming trend is under way in Antarctica will be the breakup of ice shelves on both coasts of the Antarctic Peninsula, starting with the northernmost and extending gradually southward.”

Mercer’s prediction has come true, and a couple of decades before he anticipated. Since he wrote those words, eight ice shelves have fully or partially collapsed along the Antarctic Peninsula, and the northwestern Antarctic Peninsula has warmed faster than virtually any place on Earth.

Just as the U.S. economy began a dramatic nosedive in 2007, so did the Arctic’s summertime sea ice. That September, the ice’s minimum seasonal extent shattered previous records. The minimums in 2008 and 2009 were somewhat less extreme, but still well below those observed in the 1980s and 1990s.

This summer, the ice—much like the economy—continues to struggle. “It’s pretty crazy that on 6 August we were already below the 1979–2000 average extent for September,” notes NCAR’s Jennifer Kay, a climate scientist focusing on processes that affect Arctic ice.

The surest sign of a warming Earth is the steady melting of its ice zones, from disappearing sea ice in the Arctic to shrinking glaciers worldwide. Now, scientists are using increasingly sophisticated satellite technology to measure the extent, thickness, and height of ice, assembling an essential picture of a planet in transition.

by michael d. lemonick