It is nearly a magical sight to wake up to the gentle snowfall on Christmas morning. When the snow is still falling two days later, the magic starts to fade. Eventually, while poking at several inches of ice, buried beneath ten inches of snow, in hopes of finding your car, what was once magic soon becomes kicking and cursing: "&#%!@* MELT ALREADY!"
But that’s the story in Colorado, at least. Elsewhere, say atop the sheet of ice covering Greenland, you might hear similar expletives, with a different tone. "&#%!@* MELT ALREADY!?" Because, as feared, Greenland is melting… but far more quickly than anyone predicted.
Water seeps up through the ice on Greenland.
Before I go into the details on this, I’d like to share my personal perspective. To put it mildly, I’m freaked out by this one. This announcement came as I was preparing for my final exams on climate change. It was eerie for a few reasons… first, it was my university that discovered the early, anomalous melting, around the same time I decided I’d made the right choice in my education. On top of that, I’ve spent the past few months obsessing over predictive science, puzzling over the ways we use models of our climate to predict future conditions. Not just puzzling-the more I understood the powerful accuracy of such predictions, the scarier those predictions seemed.
But here’s the disturbing part-those predictions do not typically include the impacts of large ice sheets like Greenland melting, because the processes involved are not very well understood. (It is a whole lot easier to predict something like the thermal expansion of sea water-ocean warms, ocean expands, sea level rises.) Our models are already on the conservative side. How conservative? Only time will tell.
So, what’s going on with Greenland? According to a recent study by the Cooperative Institute for Research in Environmental Studies at CU Boulder, the extent of melting this past summer was the largest on record.
Professor Konrad Steffen, who has been monitoring Greenland’s melting through a "Climate Network" of 22 stations around the ice sheet, described both the extent of melting and the potential dangers. According to the climate scientist, air temperatures over Greenland have increased by 7 degrees Fahrenheit since 1991.
Seven degrees? This seems like quite a bit… after all, the IPCC projections suggest just two to three degrees of warming over the next century… what’s up with seven in a decade? The important thing to remember here is that the earth does not heat evenly. While the overall global predictions are for a few degrees, that is the average-some areas will face extremes.
Geography plays an important role. The oceans can take quite a bit of heat without changing much, while the land tends to retain the heat, and thereby show more warming. The northern hemisphere has much more land than the southern, so we can expect more warming to occur in the north.
This extreme polar warming has begun to show in both the Arctic Ocean and the Greenland Ice Sheet. Concerning the latter, Professor Steffen explained that even an increase in snowfall is not enough to offset the melting:
Although Greenland has been thickening at higher elevations due to increases in snowfall, the gain is more than offset by an accelerating mass loss, primarily from rapidly thinning and accelerating outlet glaciers, Steffen said. "The amount of ice lost by Greenland over the last year is the equivalent of two times all the ice in the Alps, or a layer of water more than one-half mile deep covering Washington, D.C."
The Jacobshavn Glacier on the west coast of the ice sheet, a major Greenland outlet glacier draining roughly 8 percent of the ice sheet, has sped up nearly twofold in the last decade, he said. Nearby glaciers showed an increase in flow velocities of up to 50 percent during the summer melt period as a result of melt water draining to the ice-sheet bed, he said.
"The more lubrication there is under the ice, the faster that ice moves to the coast," said Steffen. "Those glaciers with floating ice ’tongues’ also will increase in iceberg production."
Rivers of ice, flowing to the sea… in a way, it sounds beautiful, if not ominous:
An iceberg calved from the Jacobshavn Glacier
The danger isn’t necessarily from an increase in iceberg production, however. Moulins, or round holes where water melts into the ice sheet, can carry water to the base of the ice sheet, and reduce the amount of friction holding the sheet in place.
Steffen and his team have been using a rotating laser and a sophisticated digital camera and high-definition camera system provided by NASA’s Jet Propulsion Laboratory to map the volume and geometry of moulins on the Greenland ice sheet to a depth of more than 1,500 feet. "We know the number of moulins is increasing," said Steffen. "The bigger question is how much water is reaching the bed of the ice sheet, and how quickly it gets there."
So, what if Greenland melts? Here are some bare facts:
- Greenland is about one-fourth the size of the United States.
- Approximately 80% of Greenland’s surface area is covered in ice.
- Greenland hosts about one-twentieth of the world’s ice.
- Greenland’s melting contributes about 0.5 millimeters annually to global sea levels.
- The ice on Greenland, if melted, would be roughly equivalent to 21 feet of global sea rise.
Even Professor Steffen agrees that IPCC predictions may have been too modest:
The most sensitive regions for future, rapid change in Greenland’s ice volume are dynamic outlet glaciers like Jacobshavn, which has a deep channel reaching far inland, he said. "Inclusion of the dynamic processes of these glaciers in models will likely demonstrate that the 2007 Intergovernmental Panel on Climate Change assessment underestimated sea-level projections for the end of the 21st century," Steffen said.
So, we may have underestimated the rise in sea level. What other changes in precipitation and temperature will show sooner than expected? I’ll leave you to ponder that-I have to go shovel more snow.