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Orbital platforms can bolster or challenge global climate change theories. Satellites have confirmed a 500,000- square-mile reduction of Arctic Sea ice since 1979. (NASA)

Keep Watching the Ice

Meet the satellites bringing data to the discussion of global warming

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(Continued from page 4)

“Stand by for table 29?” Bunch asks, referring to software that will pave the way for ICESat to receive the latest set of operating commands.

“Okay for 29,” replies Faber.

With the commands on their way, Faber quickly checks the status of the laser system. Among the streams of acronyms and numbers that fill his computer screen are eight circular “gumballs” summarizing the status of ICESat’s critical systems.

All eyes are on the gumball labeled “Thermal.” It has come up a happy green. If it were red, cell phones and pagers would have sounded from Colorado to Maryland as engineers got to work figuring out how to cool ICESat’s last laser before it burned out. Just to be safe, Faber checks more temperature readings. “Everything is fine,” he says.

Engineers hope to squeeze another five or six campaigns out of Laser 3, ICESat’s last fully functional laser. Despite the problems, Zwally counts the launch of ICESat in January 2003 as his biggest achievement at NASA. Still, he will be the first to say that scientists cannot rely on space-based sensors alone to answer questions about Earth’s glaciers. Sometimes they need to get close.

At the Swiss Camp, Zwally ventures out by snowmobile to drill holes in the ice and insert poles equipped with GPS receivers. As the glacier moves, the GPS units will move with it, and Zwally will record its speed.

When Zwally started this GPS research in the mid-1990s, fellow glaciologists were surprised by his results. The Jakobshavn Glacier was accelerating during Greenland’s summer months and slowing in the winter. The finding flew in the face of something glaciologists believed about glaciers.

“Ice is a very poor [thermal] conductor, so changes on the surface don’t get into the ice very fast," Zwally says. “It takes tens of thousands of years.” So how then could an entire glacier react to temperature changes that last only a season?

In considering the question, Zwally remembered flying over a glacier and watching water flowing into it from surface lakes and ponds. The water was channeled into tunnels glaciologists call moulins.

Zwally published the now widely accepted hypothesis that water flows through the moulins all the way to the bottom of the glaciers, where the water acts as a lubricant between the rock and the ice.

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