Using this graphic and referring to it is encouraged, and please use it in presentations, web pages, newspapers, blogs and reports.
For any form of publication, please include the link to this page and give the cartographer/designer credit (in this case Philippe Rekacewicz, UNEP/GRID-Arendal)
Climate change 1995, The science of climate change, contribution of working group 1 to the second assessment of the intergovernmental panel on climate change, UNEP and WMO, Cambridge university press, 1996; Sea level rise over the last century, adapted from Gormitz and Lededeff, 1987
Uploaded on Wednesday 22 Feb 2012
Sea level rise due, past and scenarios due to global warming
Philippe Rekacewicz, UNEP/GRID-Arendal
Over the last 100 years, the global sea level has risen by about 10 to 25 cm. Sea level change is difficult to measure. Relative sea level changes have been derived mainly from tide-gauge data. In the conventional tide-gauge system, the sea level is measured relative to a land-based tide-gauge benchmark. The major problem is that the land experiences vertical movements (e.g. from isostatic effects, neotectonism, and sedimentation), and these get incorporated into the measurements. However, improved methods of filtering out the effects of long-term vertical land movements, as well as a greater reliance on the longest tide-gauge records for estimating trends, have provided greater confidence that the volume of ocean water has indeed been increasing, causing the sea level to rise within the given range.
It is likely that much of the rise in sea level has been related to the concurrent rise in global temperature over the last 100 years. On this time scale, the warming and the consequent thermal expansion of the oceans may account for about 2-7 cm of the observed sea level rise, while the observed retreat of glaciers and ice caps may account for about 2-5 cm. Other factors are more difficult to quantify. The rate of observed sea level rise suggests that there has been a net positive contribution from the huge ice sheets of Greenland and Antarctica, but observations of the ice sheets do not yet allow meaningful quantitative estimates of their separate contributions. The ice sheets remain a major source of uncertainty in accounting for past changes in sea level because of insufficient data about these ice sheets over the last 100 years.