Using the 347 million measurements, Davis created a map of East Antarctica that showed where it had gained and lost mass during the 11 years. The map did not include any points south of 81.6 degrees latitude because the satellites' orbits did not include that part of the globe. The map also did not include much data for the coasts because the equipment on the satellites often needed 20 to 30 kilometers to transition from the ocean to a solid surface. As a result, Davis drew conclusions only about changes to East Antarctica's interior, not its coast.

On average, he found the surface within his study area increasing in elevation at a rate of 1.8 centimeters a year. Across the whole area of study, those 1.8 centimeters translate to 45 billion metric tons of water added to the ice sheet each year, which is the equivalent of the top .12 millimeters of Earth's oceans. If the southern area of East Antarctica -- the part the satellites did not cover -- gained mass at a similar rate, Davis says, the increase would equal closer to 0.18 millimeters off the top of Earth's oceans.

So what's causing the buildup on East Antarctica? Probably an increase in snowfall, Davis says. That conclusion coincides with a prediction made in the IPCC assessment. Using a variety of climate-forecasting models, the IPCC predicted global warming would lead to an increase in precipitation over Antarctica. That's because warmer air can hold more moisture. In Antarctica, the models show the air temperature increasing enough to produce more snowfall but nowhere near enough to cause surface melting. More snow with no increase in melting means a slow but steady buildup on the surface, which means an increase in surface elevation.

To test whether increasing snowfall was indeed the cause of the buildup, researchers needed ice-core records. Only these could show conclusively how much snow had fallen in previous years. Unfortunately, there is very little ice-core data for East Antarctica, Davis says, so he and his fellow researchers analyzed snowfall data from a European weather forecasting model. This showed snowfall apparently did increase in East Antarctica over the time period of the study. Still, Davis cautions that the model is not infallible -- "not perfect, but good," is how he puts it. Nor can he say his team has achieved "incontrovertible observational evidence" to support their theory. What he can say is that their findings fit the weather-forecasting model's predictions, and that other studies have indicated the model is reliable.

"We do not have 100 percent indisputable proof [that the growth was due to snowfall]," Davis says. "To put it in legal terms, we have a preponderance of the evidence. We don't have proof beyond a reasonable doubt. Some people are arguing we're wrong."

One of those people is Ian Joughin from the University of Washington, who says the growth could be the result of a damming effect along the coastal areas. He hypothesizes that glaciers are flowing more slowly along parts of Antarctica's coast than they have in the past.

"If the glaciers were flowing slower in the coastal areas, then they'd drain the ice from the interior at a slower rate, and it can back up," Davis explains. That too, he concedes, could explain the increase in surface elevations.

Published by the Office of Research.

©2006 Curators of the University of Missouri. Click here to contact the editor.