The view from the Palmer is so blindingly white today that the eye cannot tell where the ice ends and the clouds begin. In this unusually icy Antarctic summer, it seems strange to contemplate melting ice. But glaciers, here and in Greenland, are melting faster than they are growing. We know that ice sheets have been around for thousands of years, but certain areas are currently melting and breaking off into the sea at rates that far exceed their growth. The breakup of 3,320 square kilometers (1,282 square miles) Larsen B ice shelf in 2002 was only the most dramatic example.
It is clear that we are losing ice faster than we have since reliable observations began. But those observations have only been made since the advent of satellites in the 1970s. How can we resolve the difference between the rates of ice sheet destruction and their long history on earth?
There are three hypotheses that I’m familiar with, but you are welcome to leave additional possibilities in the comments. The first is that global climate change is responsible. This makes intuitive sense, as we associate warmer temperatures with melting. But air temperatures, at least, are so far below freezing in most of Antarctica that raising them a few degrees will not lead to melting. On the other hand, glacial dynamics are not well understood, and temperatures in the water underneath ice sheets are hard to measure and could have a large effect.
Another possibility is that ice sheets are still responding to the last ice age. They could still be reaching equilibrium with our modern, pre-industrial climate. There is evidence that the increase in sea level, which began as the ice age ended, has slowed considerably in the last seven thousand years but is not quite over.
A third alternative is that short-term ice sheet variability is simply much larger than long-term variability. There is limited evidence from western Antarctica that glaciers can flow quickly for years and then stop abruptly.
The difficulty now is that we simply don’t have enough data to evaluate these hypotheses. That’s why the Nathaniel B. Palmer is trying to push through the seemingly impenetrable ice to reach the Larsen area. If we can get there and examine the local glacial history of the area, we may be able to place the Larsen breakup in historical context and understand what it means for the rest of the world and for the future.
Thanks to Greg Balco from the Berkeley Geochronology Center for his explanation of glacial geology.