Global Warming - A Chilling Possibility

Global warming could plunge North America and Western Europe into a deep freeze, possibly within only a few decades.

That's the paradoxical scenario gaining credibility among many climate scientists. The thawing of sea ice covering the Arctic could disturb or even halt large currents in the Atlantic Ocean. Without the vast heat that these ocean currents deliver - comparable to the power generation of a million nuclear power plants - Europe's average temperature would likely drop 5 to 10°C (9 to 18°F), and parts of eastern North America would be chilled somewhat less. Such a dip in temperature would be similar to global average temperatures toward the end of the last ice age roughly 20,000 years ago.

Some scientists believe this shift in ocean currents could come surprisingly soon - within as little as 20 years, according to Robert Gagosian, president and director of the Woods Hole Oceanographic Institution. Others doubt it will happen at all. Even so, the Pentagon is taking notice. Andrew Marshall, a veteran Defense Department planner, recently released an unclassified report detailing how a shift in ocean currents in the near future could compromise national security.

"It's difficult to predict what will happen," cautions Donald Cavalieri, a senior scientist at NASA's Goddard Space Flight Center, "because the Arctic and North Atlantic are very complex systems with many interactions between the land, the sea, and the atmosphere. But the facts do suggest that the changes we're seeing in the Arctic could potentially affect currents that warm Western Europe, and that's gotten a lot of people concerned."

There are several satellites keeping an all-weather watch on ice cover in the Arctic. NASA's Aqua satellite, for instance, carries a Japanese-built sensor called the Advanced Microwave Scanning Radiometer-EOS ("AMSR-E" for short). Using microwaves, rather than visible light, AMSR-E can penetrate clouds and offer uninterrupted surveillance of the ice, even at night, explains Roy Spencer, the instrument's principal investigator at the Global Hydrology and Climate Center in Huntsville, Alabama. Other ice-watching satellites, operated by NASA, NOAA and the Dept. of Defense, use similar technology.

The view from orbit clearly shows a long-term decline in the "perennial" Arctic sea ice (the part that remains frozen during the warm summer months). According to a 2002 paper by Josefino Comiso, a climate scientist at NASA's Goddard Space Flight Center, this year-round ice has been retreating since the beginning of the satellite record in 1978 at an average rate of 9% per decade. Studies looking at more recent data peg the rate at 14% per decade, suggesting that the decline of Arctic sea ice is accelerating.