Global Climate Change

If it had been suggested prior to the 1980s that the study of ice— that is, glaciology—would be the key to initiating international action on global climate change, most climate scientists would probably have laughed. However, that is exactly what occurred. The kick-start came from the Vostok ice core, a project that had been underway at the Soviet station at the Pole of Inaccessibility in East Antarctica since the 1970s. By the mid-1980s, the French were in close partnership with the Soviets; in 1987, they jointly published their results on the stable water isotopes and greenhouse gas concentrations (methane and carbon dioxide, CH4 and CO2) identified in air bubbles in the core.

The paleoclimate record that has been obtained from ice cores drilled in Antarctica and Greenland represents global climate variability on timescales of millennia and longer. Faster fluctuations are affected by the local peculiarities of Antarctica and Greenland, leading to interesting differences in the ice core records . These differences are fundamentally caused by two factors. First, Greenland is located south of the Arctic Ocean, and many other landmasses are located almost as far north as Greenland. Eastern Canada and Scandinavia were occupied by large ice sheets during the glacial periods, which dominated the last few hundred thousand years, whereas Greenland is the only Northern Hemisphere ice sheet existing during the relatively short (10000 year) interglacial periods.
The 3 km high Laurentide Ice Sheet and Scandinavian Ice Sheet produced different atmospheric circulation patterns than those seen today. In contrast, Antarctica is surrounded by the Southern Ocean, along with other significant landmasses that are located too close to the Equator to support large ice sheets, even during the cold glacial periods; therefore, the main circulation patterns remain largely unaltered over glacial cycles. The second reason why Greenland reacts differently than Antarctica is the role of the North Atlantic Ocean in circulating warm tropical ocean waters to the north and into the Arctic seas. At present, these currents provide about 30% of the heat to Northern Europe, making that region much warmer than corresponding latitudes in Asia. This system (known as the Atlantic meridional overturning circulation, AMOC) appears to be rather sensitive to changes in the density and temperature structure of the ocean.

The important question challenging many ice modelers today is, how much sea level rise can we expect to come from the ice sheets over the next century or two? This question was brought into focus by the recent dramatic breakup of many large ice shelves around the fringes of Antarctica , and by the suggestion that past sea level rise sensitivity and response speed to warming was far faster all the way to its base, even hundreds of meters below the surface, in a process known as ‘‘hydro-fracturing.”

The second process is via basal melting and weakening by warm ocean water, which can typically deliver an order of magnitude more heat to the ice shelf than the atmosphere does. As the ice shelf thins, it becomes unable to support its own weight, and simply breaks apart behaving as a self-organized critical system.