Arctic ice cover for winter maximum and summer minimum for 1980 and 2007

There is now little doubt that the temperature on Earth is rising due to increased concentrations of greenhouse gases in the atmosphere. During the course of the last century, the average global surface temperature rose by about 0.6°C and 10 of the warmest years on record have occurred since 1997. Scientists are predicting that average global temperatures will rise by 4°C by the end of the century.

How rising temperatures will affect Earth’s ice is still a hotly debated issue. However, recent evidence strongly suggests that ice cover is diminishing. One of the most dramatic signs of climate change has been seen in the extent of Arctic sea ice. Since 2000, the area of the Arctic Ocean covered by ice in the summer has reduced drastically, with the minimum recorded occurring in September 2007. 2008 would have been a new record if it had not been for 2007, and 2009 was similar.

There is also emerging evidence of changes to continental ice cover. Before 2000, indications were that Earth’s two major ice caps, covering Antarctica and Greenland, were generally stable, at least in their interiors. However, it is now known that the ice caps are melting at their base, caused by warming oceans. It has been discovered that a large glacial basin at the coastal boundary of West Antarctica – the Pine Island Glacier – is thinning at a rate of 16 m per year, acting as a huge drainage basin. Satellites also continue to observe the break up of the Wilkins Ice Shelf on the southwest side of the Antarctic Peninsula. In April 2009, rifts that had developed on the ice shelf led to the collapse of the ice bridge that connected it to Charcot Island.

ESA's ice mission

New information about changes in continental ice cover has led to a projection of sea-level rise in the order of 1.4 m by 2100. This figure, cited in the 2009 report by the Scientific Committee on Antarctic Research Antarctic Climate Change and the Environment, is significantly higher than the 28–43 cm projections by the Fourth Assessment Report of the Intergovernmental Panel on Climate Change in 2007.

While there seems to be clear evidence that Earth’s ice is changing, the real question is by how much. Reductions in the area of sea ice are readily observable using a variety of satellite remote-sensing techniques; however, there is only one practical way of converting this knowledge of ‘area’ of sea ice into ‘volume’ of sea ice. To do this conversion, information about ice thickness is needed – which is what CryoSat will measure.