Warming signs: thinner glaciers and saltier oceans

Earth has a message for global warming skeptics: Its effects are starting to appear where it really counts. Antarctic glaciers are melting faster than scientists had thought. The tropical "firebox" that drives the atmosphere's weather machine is running hotter. These two developments could significantly change our planet's weather patterns.

Roughly speaking, Earth's weather machine is like a steam engine with a boiler (the tropical and subtropical oceans) and a condenser (the cooler higher latitudes). Masses of water vapor flow into the atmosphere from the boiler and travel north or south. These masses condense into rain or snow, releasing the heat they absorbed when they evaporated. Much of the water finds its way to the polar seas and flows back to the tropics.

This interchange maintains our planet's distribution of solar heat and fresh water. Research suggests that this heat/moisture distribution is changing, which could shift the location and timing of rainfall, droughts, and floods.

The telltale signal: salt. When the boiler evaporates seawater, it leaves salt behind. The hotter the boiler, the saltier the water. Indeed, the tropical seas across the Atlantic are getting saltier, according to a Nature article last December by Ruth Curry at the Woods Hole Oceanographic Institution in Massachusetts and colleagues - and an update by her last month.

To suggest that this condition is causing the rise in Atlantic hurricane activity would be a stretch. But Dr. Curry and her associates think the accumulation of salt probably is linked to global warming.

Antarctica also shows signs of a significant climate change. Three international studies reported by NASA on behalf of the various research teams show more ice loss and glacial movement than had been expected. While glaciers all over the world are losing ice, the release of vast water masses locked in Antarctic land-based ice would cause the biggest rise in sea level.

The studies show western Antarctic glaciers are shrinking "substantially" faster than observed in the 1990s, NASA reports. "They are losing 60 percent more ice into the Amundsen Sea than they accumulate from inland snowfall."

Moreover, ice shelves floating in that sea appear to be thinning. Such shelves put brakes on the speed with which inland glaciers can slide into the sea. Removing the shelves would uncork a rapid glacier advance that could raise sea level significantly. Right now, Antarctic melting contributes about 10 percent of the annual 1.8 millimeter rise (about 1/16th of an inch) in sea level. Pull out the cork and you're looking at a potential 39-inch rise in sea level all over the world.

The studies cover too short a time to prove whether the glacier changes are part of a natural cycle or a response to global warming. The scientists suspect warming. If they're right, the melting shows how fast big changes can happen.

"If anyone was waiting to find out whether Antarctica would respond quickly to climate warming, I think the answer is 'yes,' " says Ted Scambos with the National Snow and Ice Data Center in Boulder, Colo.

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