Nature Magazine - A new view on sea level rise

The IPCC's (Intergovernmental Panel on Climate Change - UN) report presented and referenced as the basis of the Copenhagen climate change accord late last year predicted sea level rise over a 100 year period averaging globally at around 1.9mm per year, for a total increase in the range of 18 to 59 cm by 2090.  However, as Nature explains this month, numerous bodies are suggesting these figures are far too low and miss critical factors which will accelerate the rate of sea level rise.

The graph above represents new modeling of sea level rise taking a more refined approach and indicates a probable sea level rise of 1 meter by 2090.  So what is lacking in the IPCC's models ?  1) They assumed a linear increase in sea level with temperature increasing and did not consider the compounding impact of warming temperatures on ice melt  2) They did not consider the impact of the melting of glaciers or the melting of the ice sheets in Antartica and Greenland. The IPCC range assumes a near-zero net contribution of the Greenland and Antarctic ice sheets to future sea level rise, on the basis that Antarctica is expected to gain mass from an increase in snowfall. Observations show, however, that both ice sheets have been losing mass at an accelerating rate over the past two decades [data : http://www.copenhagendiagnosis.org/ ]. 3)  The melting of all glaciars alone will add 60 cm to global sea levels, not including the vast continental ice sheets of Greenland and Antartica [ data : http://climatecongress.ku.dk/pdf/synthesisreport/ ].

This new and more refined view of probable sea level change is gaining traction and consensus with a growing body of the scientific community [1].   The 1 meter increase is not the worst case scenario in these new models by a long shot, indeed, it is the predicted middle scenario of 3 degrees celsius temperature increase.  The outer range of the models indicate the worst case scenario, not necessarily the most likely.

Nature magazine covers this refinement of project sea level rise quite comprehensively this month, and goes on to provide some historic context :

At the end of the last ice age, the Earth slowly warmed by 4–7 °C globally and lost almost two-thirds of its land ice in the process. That raised sea level by 120 metres, at rates often exceeding a metre per century. It seems that nothing in the present ice-sheet configuration would rule out similar rates in future. How much of the remaining 65 metres' worth of land ice will humans melt if we warm the planet by a further several degrees?

[ source : http://www.nature.com/climate/2010/1004/full/climate.2010.29.html#B17 ]


1 - [ references : http://www.sciencemag.org/cgi/content/abstract/315/5810/368 ; Vermeer, M. & Rahmstorf, S. Proc. Natl Acad. Sci. USA 106, 21527–21532 (2009). ; Horton, R. et al. Geophys. Res. Lett. 35, L02715 (2008). ; Grinsted, A., Moore, J. C. & Jefrejeva, S. Clim. Dynam. 34, 461–472 (2009). ; http://www.agu.org/pubs/crossref/2010/2010GL042947.shtml ]