Increasing Antarctic Snowmelt Largest Potential for Sea Level Rise

In a new NASA study, researchers using 20 years of data from space-based sensors aboard satellites have confirmed that Antarctic snow is melting farther inland from the coast over time. It is melting at higher altitudes than ever and there is increasing melting on Antarctica's largest ice shelf.

Antarctica is so vast with such a varied topography that only satellites can actually capture the extent of changes in amount of snow melting across the many valleys, mountains, glaciers and ice shelves.

Antarctica has a limited area where snow melting is expected to occur because even during summer months most of Antarctica records temperatures well below zero. Yet, satellite data collected between 1987 and 2006 show snow melting in unlikely places. Snow melting was found as far inland as 500 miles away from the anrarctic coast. Similarly melting was found as high up as 1.2 miles above sea level in the Transantarctic Mountains.

The NASA study using 20-year old data records covered a time period three times longer than any previous studies. It reaffirmed through satellite data the extreme melting irregularities observed in 2005.

Antarctica has a surface size that is about 1.5 times the size of the United States. Within that vast area, Antarctica contains 90 percent of Earth's fresh water. This, of course, makes it the largest potential source of sea level rise. Significantly, the 20-year period studied showed that melting had increased on the Ross Ice Shelf that sits at the edge of the sea. This finding was in terms of the area affected by the increased melting and the duration of melting across affected areas--quantity and duration over expanse.

The satellite data was collected from the Special Sensor Microwave Imager radiometer aboard the Defense Meteorological Satellite Program's satellites. The microwave sensors showed evidence of persistent snow melting, which is defined as melting that occurs for at least three days or, alternatively, for one consecutive day and night.

Microwave instruments offer a benefit to the researchers over visible sensors. As the sensors fly over Antarctica, they measure the radiation naturally emitted by snow and ice at microwave frequencies. Unlike visible sensors, Microwave instruments can also detect melting below the snow surface.

"Microwave instruments are very sensitive to wet snow and can see through clouds day and night, allowing us to separate melting from dry snow to better understand when, where and for how long melting took place," said lead author Marco Tedesco, a research scientist at the Joint Center for Earth Systems Technology cooperatively managed by NASA's Goddard Space Flight Center, Greenbelt, Md., and the University of Maryland at Baltimore County, Baltimore.

"Satellites have given us a remarkable ability to monitor the melting trends of glaciers and ice shelves on this immense and largely unknown continent, and to watch for unusual occurrences like those observed in 2005," said co-author Waleed Abdalati, head of the Cryospheric Sciences Branch at NASA's Goddard Space Flight Center. "Through this space-based perspective, we are really only just beginning to understand the nature of the changes that are occurring in Antarctica, and what these changes will mean for Antarctica's future contributions to sea level."

It is now known that when there is an increase in surface snowmelt, snowmelt on the ice shelf surface can lead to melt ponds, with meltwater filling small cracks. The liquid water puts pressure on the cracks causing larger fractures in the ice shelf.

He further stated that "Snow melting is very connected to surface temperature change, so it's likely warmer temperatures are at the root of what we've observed in Antarctica."

The study's results based on the satellite microwave data support related research that reports a direct link between changes in near surface air temperatures and the duration and geographic area of snow melting on Antarctica. These studies, when taken together, indicate a relationship to climate change.

Although the researchers observed less melting in some locations on the continent during the 20-year period, melting increased in other places. Most significant is the increased snowmelt on the Ross Ice Shelf.

Tedesco points out that "Persistent melting on the Ross Ice Shelf is something we should not lose sight of because of the ice shelf's role as a 'brake system' for glaciers...Ice shelves are thick ice masses covering coastal land with extended areas that float on the sea, keeping warmer marine air at a distance from glaciers and preventing a greater acceleration of melting. The Ross Ice Shelf acts like a freezer door, separating ice on the inside from warmer air on the outside. So the smaller that door becomes, the less effective it will be at protecting the ice inside from melting and escaping."

The study, authored by Tedesco and Abdalati, will be published in the American Geophysical Union's Geophysical Research Letters.

"NASA Researchers Find Snowmelt in Antarctica Creeping Inland," NASA.