The 2009 Copenhagen Diagnosis [1] used satellite data, dating back to advent of its use in 1993, to update predictions of sea level rise made by the International Panel on Climate Change (IPCC) in the 2001 Third Assessment Report (TAR) [2] and the 2007 Fourth Assessment Report (AR4) [3].
The findings indicated an 80% increase of the most sever IPCC prediction. A point made even more sobering when it is considered that the prediction was based on the following assumptions:
- Top level of pollutant emissions
- Top level of climate sensitivity
- Ad hock measurement of sea level rise, due to the uncertain input from ice sheet melt [4].
The predictions of increase have been supported by studies of ocean warming, which identified thermal expansion of the oceans as some 50% greater than IPCC projections [5]. Further support came with observations of the actual rise in sea level between 1987 and 2007 indicating a rise 25% higher than any predictions made in the past 115 years [6].
There were two main causes identified for the of sea level rise between 1961 and 2003 [1]:
- Thermal expansion of the oceans, caused by an increase in energy supplied to particles within the water column: 40%
- Continental ice sheet melt, particularly the ice sheets of Greenland and Antarctica: 60%
It was a single advancement in technology bought about fears of an acceleration in sea level rise and forced the increases in estimations: satellite observation of ice sheet dynamics [7].
The Ice Sheets
In both the 2001 and 2007 IPCC sea level rise predictions, ice sheet dynamics were not properly understood or acknowledged. For example in the AR4 predictions [3], Antarctica was identified as a land form responsible for countering a rise in sea levels during the 21st century. Such a point that was reversed during the creation of the 2009 predictions [1] and resulted in the doubling of the observed contribution of ice sheet melt to sea level rise.
Concerns were raised again when it was realised that doomsday scenario of the complete disappearance of the Greenland and Antarctic ice sheets would result in nearly a 60 metre rise in sea levels [1], the effects of which can be seen in the video below.
The two major continental ice sheets of Greenland and Antarctica are those under the most scrutiny, information of which follows:
Greenland: The IPCC AR4 identified the Greenland ice sheet as contributing between -0.07 and 0.17 millimetres a year to sea level rise between 1961 and 2003, a point that aptly illustrates the lack of knowledge of the IPCC in 2007 [3].
However, after satellite monitoring allowed further study, it was identified that the loss of ice sheet mass from Greenland had doubled between 2002 and 2009 [8]. It was also found that surface temperatures had increased by more than 1.5 times between 2002 and 2006, two points that could greatly increase the effect of Greenland ice melt on sea levels (figure 1)
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| Figure 1: The general increase in summer melt area of the Greenland ice sheet. two diagrams illustrate the difference between 1992 and 2007 total melt area (coloured in red) [1] |
Antarctica: Being one of the most hospitable places on earth, little was known of Antarctica ice shelf dynamics before the use of satellite observation. However, a change in the view of ice sheets came with the observation; the reliable and slowly changing masses were discovered to be rapidly changeable and easily affected landforms [7].
The research revealed that the solid land supported, east of Antarctica was far more stable than the west and the Antarctic peninsula, both of which were susceptible to ice shelf collapse. Ice sheet collapse occurs when an already floating ice shelf is warmed by ocean waters from beneath and breaks away from the ice sheet [7]. After such an event occurs, glacier flow increases in speed, unimpeded by and previous resistance, [ 7].
The video below documents the collapse of the northern point of the Larsen b ice shelf of the Antarctic Peninsular, a loss of 3,250 square kilometres of ice in just over a month. This collapse allowed a tenfold increase in glacier flow [7].
Such an occurrence could severely increase the inflow of melt water from the Antarctic ice sheets, as increase glacier flow delivers ice to the coasts and brings it into contact with a warmer ocean.
It was the realisation of these facts that bought polar warming to the forefront of sea level study.
However, the knowledge of the earth's reactions to global warming is still thin in areas, an example of which can be seen in the observations of Stefan Rahmstorf [4]. Modern modelling systems are failing to model the changes in sea level that have been observed over the past decades, indicating that something is still missing from the calculations.
This point illustrates the need to study past sea level changes, in an effort to aid predictions of future changes; it is this subject that my next post will cover.
References
[1] Allison, I. , N.L. Bindoff, R.A. Bindschadler, P.M. Cox, N. de Noblet, M.H. England, J.E. Francis, N., Gruber, A.M. Haywood, D.J. Karoly, G. Kaser, C. Le Quéré, T.M. Lenton, M.E. Mann, B.I. McNeil, A.J. Pitman, S. Rahmstorf, E. Rignot, H.J. Schellnhuber, S.H. Schneider, S.C. Sherwood, R.C.J., Somerville, K. Steffen, E.J. Steig, M. Visbeck, A.J. Weaver, (2009) The Copenhagen Diagnosis, Updating the World on the Latest Climate Science. The University of New South Wales Climate Change Research Centre (CCRC), Sydney, Australia.
[2] Inter Governmental Pannle on Climate Change (2001) IPCC Third Assessment Report: Climate Change 2001 (TAR) [online]. Available at: http://www.grida.no/publications/other/ipcc_tar/ [02.03.2010]
[3] IPCC, (2007) Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC, Geneva, Switzerland.
[4] Rhamstorf, S (2007) A Semi-Empirical Approach to Projecting Future Sea-Level Rise. Science 315, 368
[5] Domingues, C.M., J. A. Church, N. J. White, P. J. Gleckler, S.E. Wijffels, P.M. Barker & J.R. Dunn, (2008) Improved Estimates of Upper-ocean Warming and Multi-decadal Sea-level Rise. Nature, 543, 19
[6] Rahmstorf, S. A. Cazenave, J.A. Church, J.E. Hansen, R.F. Keeling, D.E. Parker, R.C.J. Somerville (2007) Recent Climate Observations Compared to Projections. Science, 316, p.709
[7] Rignot, E. (2006) Changes in ice dynamics and Mass Ballance of the Antartic Ice Sheet. Physolophycal Transitions of the Royal Society, A. 364, 1637-1655
[8] Velicogna, I., (2009) Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE. Geophysical Research Letters 36, L19503.
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