Chapter 5 - Land Ice: Indicator and Integrator of Climate Change

Abstract

Land ice, in the form of glaciers, ice caps and the great ice sheets that cover most of Antarctica and Greenland, constitute some 70% of the total freshwater store of the planet. Combined, they have the potential to raise global mean sea level by 66.5m. The vast majority of this frozen water store is contained in the ice sheets and they, therefore, present the greatest potential threat to future sea level rise. Glaciers and ice caps, however, for most of the twentieth century have been the largest land ice contributor to sea level, despite their much smaller volume and area. That is partly because of their ability to respond more rapidly to changes in climate compared to the ice sheets. It is also partly because the greatest volume of glaciers and ice caps lies in areas that are experiencing enhanced warming – namely the Arctic and Antarctic Peninsula – compared to the global average. This phenomenon, known as polar amplification, is predicted by coupled Atmosphere-Ocean General Circulation Models and has been identified in the paleo-climate record. It suggests that the polar regions will experience about a one-and-a half to two times greater temperature increase compared to the global mean in the future. The idea that, in general, land ice will melt faster in a warmer world is not controversial, nor is the principle of polar amplification. Thus, concern about the future of glaciers and ice sheets is warranted and monitoring their changing mass is a high priority. In the last two decades, our ability to monitor these changes has undergone a revolution. The launch of the European Remote Sensing satellite, ERS-1, in 1991, along with a suite of subsequent missions, has allowed us to measure changes in volume, mass and speed of glaciers, ice caps and sheets around the world with unprecedented accuracy and resolution. In almost every location, and going from small valley glaciers, a few kilometres in length, to a vast ice sheet covering nearly 2million square kilometres, we have witnessed dramatic changes and accelerating mass loss.