Sea levels have been rising slowly for the past century. This rise is 40% due to thermal expansion of the oceans, because as global warming heats the seas, the water expands. 60% of the observed sea level rise is caused by runoff from melting ice that results from rising global temperatures.
Sea levels are currently rising by about 3.4 mm per year, while the average for the 20th century was only 1.7 mm.
The most recent IPCC report (2007) predicted around half a meter of sea level rise by 2100, but the authors deliberately omitted from their calculation the contribution of thawing of the polar ice caps and Greenland, which could not be accurately predicated. The broad concensus currently favours a figure of 1-2 meters by 2100, but significant uncertainties surround the upper figure.
If uncontrolled warming should destabilise the polar regions, far greater rises remain possible.
James Hansen, head of NASA’s Goddard Institute for Space Studies, has argued in the past that the world could conceivably face up to 5 meters of sea level rise by century’s end if greenhouse emissions continue to rise unimpeded. Such a rise would have catastrophic effects.
Due to the profile of beaches, and their vulnerability to seasonal storm surges, sea level rise of just a few centimeters can result in many meters of erosion inland.
Thus in many places, even 50 centremetres sea-level rise – the minimum rise predicted – means that entire beaches will be washed away, together with a significant chunk of coastline. For people on low-lying islands like Tuvalu, Kiribati and the Maldives, where the highest points are just 2-3 metres above sea level, that extra 50 centimetres could see significant portions of their habitable land being washed away by erosion or covered by water.
If sea levels rise by just one or two metres, some island nations will completely disappear, leaving only the millions of environmental refugees behind. More worrying still, the coastal regions of densely populated nations such as Pakistan, India, Sri Lanka, Bangladesh and Burma – home to many of the world’s poorest people – will be dramatically reduced by flooding.
This means that rising sea levels will affect those who have contributed the least to climate change, and those least able to cope with its impacts.
Not only the developing world will be affected by rising sea levels. London, New York and Shanghai will be forced to spend billions on flood defenses.
Robin McKie, ‘Scientists to issue stark warming over dramatic new sea level figures’, The Guardian, 8 March 2009, http://www.guardian.co.uk/science/2009/mar/08/climate-change-flooding; Ian Ammison, et. al., 2011, ‘The Copenhagen Diagnosis: Updating the world on the latest climate science’, Elsevier, p. 51.
Ian Ammison, et. al., 2011, ‘The Copenhagen Diagnosis: Updating the world on the latest climate science’, Elsevier, p. 51.; United Nations Environment Program, ‘Global outlook for Ice and Snow: Highlights’, 2007, p. 14, http://www.unep.org/geo/GEO_Ice/PDF/GEO_C1_LowRes.pdf
Ian Ammison, et. al., 2011, ‘The Copenhagen Diagnosis: Updating the world on the latest climate science’, Elsevier, p. 51.
James Hansen, ‘Huge sea level rises are coming – unless we act now’, New Scientist, 25 July 2007, http://www.newscientist.com/article/mg19526141.600-huge-sea-level-rises-are-coming–unless-we-act-now.html?page=1
NOVA, ‘Getting into hot water – global warming and rising sea levels’, Australian Academy of Science, May 2008,http://www.science.org.au/nova/082/082key.htm
Hannah Devlin and Robin Pagnamenta, ‘Major Cities at Risk from Rising Sea Level Threat’, Times Online, December 2009,http://www.timesonline.co.uk/tol/news/environment/article6938356.ece