Keep Watching the Ice

Meet the satellites bringing data to the discussion of global warming

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)
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IN EARLY MAY, WHEN MOST PEOPLE in the United States enjoy the warm days of spring, veteran NASA glaciologist Jay Zwally instead heads north to the ice-bound edge of western Greenland.

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It takes two aircraft, an LC-130 transport and a de Havilland Twin Otter, to get him to a collection of tents pitched on a wooden platform, known by glaciologists as the Swiss Camp. The name is a remnant of its origins as a research site operated by a Swiss university, now used by NASA and others to measure the effects of climate change.

Just south of the camp lies the Jakobshavn Glacier, a thick slab of ice that is gradually sliding downhill toward the Greenland coast. At the water’s edge it becomes the Jakobshavn Isbrae, a tongue of ice spilling into a natural inlet. The surface of the glacier melts in the summer, and Zwally needs to prepare his Global Positioning System sensors in the ice to measure how the surface water affects the glacier’s velocity.

When Zwally is not on the glacier, he’s in Maryland running the science side of a $283 million NASA satellite project that is watching it. Whether deploying equipment on the ice or into orbit, he is seeking data to answer some of the thorniest questions in the debate over global climate change: How quickly will Earth’s ice melt as the planet continues its expected warming trend, and what will the extra water do to sea levels?

In the community of glaciologists, Zwally’s training as a mechanical engineer and physicist is unusual. As a young engineer in the 1960s, he built part of a solar wind detector that flew aboard NASA’s Explorer 34 scientific satellite. He then earned a Ph.D. in physics from the University of Maryland but couldn’t find a job in that field. “I got this wonderful opportunity to go to the National Science Foundation and I got into glaciology, polar research,” Zwally says. In 1974, he moved to NASA, and now works at the Goddard Space Flight Center in Greenbelt, Maryland.

In the mid-1980s, Zwally first conceived of a satellite that could measure Earth’s ice by bouncing infrared laser pulses off Earth’s ice sheets. In January 2003, NASA launched the Ice Cloud and Land Elevation Satellite, or ICESat, with Zwally serving as project scientist. Forty times a second, ICESat fires its laser, catches the reflections with its telescope, and calculates the height of the ice based on how long it takes the signals to return.

ICESat’s altimeter data will enable scientists to calculate the volume of the ice still present in Earth’s glaciers. By comparing the measurements taken over the life of the satellite, scientists will figure out whether Earth’s glaciers overall are losing or gaining ice, and if so how much.

ICESat is one of two satellite systems NASA is counting on to make the first truly quantitative, three-dimensional measurements of the planet’s ice cover. The second system, the Gravity Recovery and Climate Experiment, or GRACE, consists of twin satellites that can sense the shrinking of ice sheets by measuring the diminishment of their gravity tug. GRACE was launched in March, 2002.

Armed with these satellite measurements, glaciologists are taking the first steps toward predicting how much ice will disappear from Earth in the coming decades—the critical figures of “how much and when,” Zwally calls them.

At the moment, water that might otherwise flood coastal cities and towns around the world remains locked away as ice, much of it in Antarctica and Greenland. “The glaciers have in them on the order of 70 meters—200 feet—of potential sea level rise,” says Bruce Wielicki, a senior scientist at NASA’s Langley Research Center in Hampton, Virginia. “No one is talking about us getting all 200 feet in the next 100 years, but the point is, even if you only got five of that 200 feet, where I live, our average elevation is about three feet. So the costs of dealing with sea level change are one of the huge potential issues.”

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