3.3. Ice sheet melting and catastrophic sea-level rise

In its 2005 report, Stabilising Climate to Avoid Dangerous Climate Change, the UK Met Office Hadley Centre estimates that even if the level of atmospheric carbon dioxide rises to four times that of pre-industrial times, it would still take around 1,000 years for half the Greenland Ice Sheet to melt, and around 3,000 years for it to disappear altogether. The meltwater contribution to sea-level rise would peak at about 5 mm a year (translating to a maximum rise of 50 cm a century) – worrying but hardly catastrophic. Observations published in just the last 12 months, however, suggest that wholesale melting may already be proceeding far more rapidly, bringing the prospect of a devastatingly rapid sea-level rise. Jim Hansen, Director of NASA’s Goddard Institute for Space Studies has voiced the opinion that collapse of the Greenland Ice Sheet could be explosively rapid, leading to sea-levels rising “a couple of metres this century and several more next century”. Referring to the Greenland and West Antarctic ice sheets, IPCC climate scientist, Michael Oppenheimer is concerned that “the time-scale for future loss of most of an ice sheet may not be millennia but centuries”