A comparison of recorded Antarctic temperatures and snowfall accumulation to predictions by major computer models of global climate change offer both good and bad news.
The good news is that the numerical models’ predictions covering the last 50 years broadly follow the actual observed temperatures and snowfall for the southernmost continent, although the observations are very variable.
The bad news is that a similar comparison that includes the last 100 years is a poor match. Projections of temperatures and snowfall ranged from 2.5 to five times what they actually were during that period.
The findings suggest that current computer models of the effects of global warming may not work as well for the remote Antarctic regions.
“It does imply that with the ocean north of Antarctica and the continent itself, there are some significant issues with the current climate models,” says David Bromwich, professor of geography at Ohio State.
Bromwich and his colleagues think they may know why the predictions vary so much from the records - they’re blaming the errors on water vapor in the atmosphere over the ice.
They suggest that long-wave radiation emitted by water vapor may be heating the ice surface and raising the temperature projected by the models.
“The models predict the water vapor,” Bromwich says, “but we don’t have anything to actually measure the amount of water vapor over the Antarctic continent. Regarding water vapor over mainland Antarctica, the models just have to be wrong.”
In their study, Bromwich, Andrew Monaghan, formerly a researcher at Ohio State’s Byrd Polar Research Center, and David Schneider from the National Center for Atmospheric Research, relied on two sets of data. One set came from observations of snowfall and temperature recorded from Antarctica since the International Geophysical Year a half-century ago. The other consisted of temperature data derived from short ice cores recovered from the continent.
This information was compared to an average taken from five of the major climate change models used by the Intergovernmental Panel on Climate Change (IPCC) for that period. While there are 23 global climate models (GCMs) available, the average of these five provided the best combination for this research.
Most worrisome is the finding that the century-long data set shows temperatures that vary from 2.5 to five times higher than actually occurred, based on the data. The models show a warming of the continent at the global rate, whereas the actual warming is much more muted.
Bromwich says that the Antarctic climate has not warmed like the rest of the globe due, in part, to the strengthening of winds around the continent. That strengthening is driven by a combination of the Antarctic ozone hole in the stratosphere, greenhouse gas increases and internal climate variability across the continent, he says.
“We don’t know how any of these factors will evolve during the coming century and therefore, there is still considerable uncertainty as to how much warming will occur in Antarctica,” he says.
“Most people are convinced that the warming along the Antarctic Peninsula is due to human influences, but the question is how far south that warming will go, and what effect it will have,” Bromwich says.
Key to this is that if melted, the ice stacked atop the Antarctic continent is enough to raise sea levels 200 feet worldwide. “That question of global sea level rise should be one that is relevant to almost everybody,” he said.
This research was largely sponsored by the National Science Foundation, with additional support from the U.S. Department of Energy.
Article: Andrew J. Monaghan, David H. Bromwich, David P. Schneider, 'Twentieth century Antarctic air temperature and snowfall simulations by IPCC climate models', GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L07502, doi:10.1029/2007GL032630, 2008