World Environment Day on June 5 focuses on climate change and its effects on ice- and snow-covered areas of the world. The theme Melting ice — a hot topic? is timely during this, the International Polar Year, and after the recent release of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report, which details the strongest evidence yet of global warming.

Today, Dr Ian Allison of the Australian Antarctic Division and Antarctic Climate and Ecosystems Cooperative Research Centre will speak about some of the changes to snow and ice cover detailed in the IPCC report. These changes include:

  • A 3.5% decrease in Northern Hemisphere (NH) spring snow cover extent since 1920, and a 7% decrease in the maximum extent of seasonally frozen ground since 1901;
  • Later freeze and earlier thaw of NH rivers and lakes, resulting in 12 days decreased duration of ice cover over 100 years;
  • A decrease since 1978 in annual Arctic sea ice extent of 2.7% per decade, a decrease in summer minimum extent of 7.4% per decade, and a decrease in Arctic sea ice thickness of up to 1 metre between 1987 and 1997;
  • Increased melting of glaciers and ice caps around the world which contributed 0.77mm per year to sea level rise between 1991 and 2004;
  • New evidence that melting of the polar ice sheets of Greenland and Antarctica is adding an additional 0.4mm/yr to sea level rise, and that the rate of melt of Greenland is increasing.

Modelling indicates that the ice sheets will continue to contribute to sea level rise. However, there is uncertainty around how much they will contribute, as scientists currently have a poor understanding of the processes involved in the ice sheets’ potentially rapid dynamic response to climate change.