Antarctica Snowfall Not Curbing Sea Level Rise, Study Says
for National Geographic News
|August 11, 2006|
Snowfall amounts in Antarctica have not increased for the past 50 years,
according to a new study.
The finding suggests that Antarctica's snowfall is not slowing the sea level rise caused by global warming, as most climate models predict.
It also supports a theory that the icy continent is mostly isolated from the rest of the world's climate system.
"Antarctica is at a really strange place within the global climate system at the moment," said Andrew Monaghan, a research associate at the Byrd Polar Research Center at Ohio State University in Columbus.
"Annual temperatures haven't changed a whole lot over the continent as a whole."
Monaghan and an international team of scientists combined data from ice cores, snow stakes, and computer models to obtain a 50-year snowfall record for Antarctica.
They found that, like the temperature, the snowfall record showed no significant change.
The team reports the finding in today's issue of the journal Science.
Claire Parkinson, a climatologist at the NASA Goddard Space Flight Center in Greenbelt, Maryland, said the discovery suggests that there is much left to learn about Antarctica's climate.
"Our understanding of what should be going on [in Antarctica] is not as complete as we might want," she said.
Prediction Versus Reality
Most climate models predict that snowfall in Antarctica would help offset the melting of glaciers on the continent's edges and elsewhere in the world.
In theory, more Antarctic snowfall would capture more of the moisture released by the melting, thereby limiting sea level rise.
The global sea level is currently rising at about 0.1 inch (2.8 millimeters) a year.
(Read "Greenland Ice Sheet Is Melting Faster, Study Says" [August 10, 2006].)
Global temperatures have risen, on average, about 1 degree Fahrenheit (0.6 degree Celsius) over the past century.
The Antarctic Peninsula, a 745-mile (1,200-kilometer) arm of land that juts north toward South America, has warmed by about 4.5 degrees Fahrenheit (2.5 degrees Celsius) since 1950.
(See an interactive Antarctica map, photos, video, and more.)
Chunks of ice the size of small U.S. states have disintegrated there in recent years.
(See video: "Huge Iceberg Crumbles Off Antarctica" [November 2005].)
But aside from the Antarctic Peninsula, the annual surface temperature over Antarctica as a whole has remained essentially the same for the past 50 years, Monaghan says.
Some studies suggest a slight cooling since the 1970s; others suggest a slight warming since the 1960s.
"But they are not statistically significant," he said. "You can't say the trend is different than zero."
The same goes for snowfall, he says.
In Science, Monaghan and colleagues write, "[t]here has been no significant change in snowfall since the 1950s."
Richard Alley is a glaciologist at Pennsylvania State University in University Park.
He explains that warmer air holds more moisture, which in the cold Antarctic should fall as snow, according to climate models.
"But the Antarctic is especially complex, in part because of the ozone hole," he said.
Previous research has found the ozone holea gap in or thinning of the upper atmosphere's ozone layerhas contributed to changes in atmospheric circulation over Antarctica.
The changes are causing the interior to cool and the Antarctic Peninsula to warm.
Monaghan likened the circulation pattern to a curtain around Antarctica, isolating the bulk of the continent from the rest of the global climate system.
As the ozone hole recovers, he adds, the study suggests that temperatures in Antarctica should come in line with the rest of the Southern Hemisphere.
"So it's important to figure out, if we see that, how snowfall changes and what impact it will have on sea level," he said.
Monaghan said he is confident that the 50-year snowfall record his team collected is scientifically robust.
Though the ice core and snow stake data are sparse, researchers were able to fill in the voids using a weather model like those used to create the forecasts on the evening news.
The scientists then performed a variety of statistical analyses on the data and recompiled the data in different ways.
"We kept getting the same answer over and over," Monaghan said. "We're pretty sure it's a good answer."
Jay Zwally, a glaciologist at the NASA Goddard Space Flight Center, says the result makes sense.
In an upcoming study on Antarctica's ice sheet, he and colleagues reach a similar conclusion.
"As we saw it, there has not been a significant increasing trend in Antarctic snowfall, except in the region of the Antarctic Peninsula," he said.
But when global temperature changes catch up in the rest of Antarctica, especially the East Antarctic ice sheet, he added, "we'll likely see an associated increase in precipitation."
According to Monaghan, the year-to-year and decade-to-decade change in Antarctic snowfall is so large that "unfortunately, it might take a while to figure out how Antarctica is fitting into the larger climate change picture."
Parkinson, also of NASA's Goddard Center, summed it up this way: "We've got a long way to go before we fully understand what's going on here."
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