Sea Level Rise
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Title:
Sea Level Rise
Creator:
R. Warrick
J. Oerlemans
Publication Date:
Language:
English

Notes

Summary:
This Section addresses three questions: Has global-mean sea level been rising during the last 100 years? What are the causal factors that could explain a past rise in sea level? And what increases in sea level can be expected in the future? Despite numerous problems associated with estimates of globally-coherent, secular changes in sea level based on tide gauge records, we conclude that it is highly likely that sea level has been rising over the last 100 years. There is no new evidence that would alter substantially the conclusions of earlier assessments regarding the rate of change. Our judgement is that: The average rate of rise over the last 100 years has been 1.0 - 2.0 mm yr t. There is no firm evidence of accelerations in sea level rise during this century (although there is some evidence that sea level rose faster in this century compared to the previous two centuries). As to the possible causes and their specific contributions to past sea level rise, the uncertainties are very large, particularly for Antarctica. However, in general it appears that the observed rise can be explained by thermal expansion of the oceans, and by the increased melting of mountain glaciers and the margin of the Greenland ice sheet. From present data it is impossible to judge whether the Antarctic ice sheet as a whole is currently out of balance and is contributing, either positively or negatively, to changes in sea level. Future changes in sea level were estimated for each of the IPCC forcing scenarios (using the same simple box model as in Section 6). For each scenario, three projections - best estimate, high and low - were made corresponding to the estimated range of uncertainty in each of the potential contributing factors. It is found that: For the IPCC Business-as-Usual Scenario at year 2030, global-mean sea level is 8 - 29 cm higher than today, with a best-estimate of 18 cm. At the year 2070, the rise is 21 - 71 cm, with a best-estimate of 44 cm. Most of the contribution is estimated to derive from thermal expansion of the oceans and the increased melting of mountain glaciers and small ice caps. On the decadal time scale, the role of the polar ice sheets is expected to be minor, but they contribute substantially to the total uncertainty. Antarctica is expected to contribute negatively to sea level due to increased snow accumulation associated with warming. A rapid disintegration of the West Antarctic Ice Sheet due to global warming is unlikely within the next century. For the lower forcing scenarios (B,C and D), the sets of sea level rise projections are similar, at least until the mid-21 st century. On average these projections are approximately one-third lower than those of the Business-as-Usual Scenario. Even with substantial decreases in the emissions of the major greenhouse gases, future increases in temperature and, consequently, sea level are unavoidable - a sea level rise "commitment" - due to lags in the climate system. This present assessment does not foresee a sea level rise of >_ 1 metre during the next century. Nonetheless, the implied rate of rise for the best-estimate projection corresponding to the IPCC Business-as-Usual Scenario is about 3-6 times faster than over the last 100 years.

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Florida International University
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