Los Alamos National Laboratory
Model Mixes Ice, Heat, Water and Salt to
View the Ocean’s Future
Looking to the Sea for Clues to the Climate
Within the next several decades, ice over the Arctic will completely disappear during the summer. That’s just one of the clear and dramatic predictions to come from models developed by the Climate Ocean and Sea Ice Modeling (COSIM) program at the Department of Energy’s Los Alamos National Laboratory.
Additionally, “The models now predict globally an average surface temperature rise of 2 to 4 degrees Celsius over the next 100 years,” says the program’s project manager, Philip Jones. And the oceans account for more than 70 percent of the Earth’s surface.
Sea ice thickness (in meters) in September 1998 from an ocean-ice simulation Click image for larger version and more information |
Jones and his group of 12 researchers use the power of supercomputer simulations to study how Earth’s oceans are affected by and influence global warming. Their specialty is modeling ocean circulation and how it affects both heat transport and sea ice up to 100 years into the future. Results from his team and other research lead Jones to conclude that some aspects of climate change could take place more rapidly than previously anticipated. “There are amazing changes going on right now,” he says.
The loss of summer Arctic sea ice provides a case in point. Satellite observations since 1978 show that the average annual sea ice shrinkage has been some 2.7 percent per decade with summertime average losses of 7.4 percent. At some point in the not-too-distant future, the ice will become so thin that one warm summer — or as Jones puts it, “one pulse of warm water” — will be enough “to cause a rapid transition to an ice-free state.” This will happen, he anticipates, within 30 to 40 years.
The loss of Arctic sea ice, dramatic as it may be, will not directly raise the sea level, since the ice already displaces water as it floats on the surface. The disappearance of sea ice can, however, indirectly affect sea level since the water temperature will rise, causing thermal expansion. This is significant because the oceans’ huge mass makes them act like a heat sink, absorbing 80 percent of the climate’s temperature increase.
The oceans also are slow to respond to a rise in global temperature, especially at depths below the top few hundred meters.
“What that means is even if we stop putting greenhouse gases into the atmosphere today, we are committed to another half-degree or so of warming just because the oceans haven’t caught up,” Jones says.
Thermal expansion is expected to increase ocean levels by some 30 centimeters over the next 100 years. That’s not a large increase, but it will affect some areas and will have secondary effects on things like storm surges. A much more dramatic rise in sea level would occur if huge land-based glaciers on Greenland and Antarctica melt — a phenomenon that’s already being observed.
