Sea level rise - Grantham Note 3

Authors: Dr Flora Whitmarsh and Dr Simon Buckle

**Update** For more up-to-date information, see our briefing: Sea level change

Overview

• Climate change causes a rise in sea level through thermal expansion of the ocean, melting of glaciers and ice loss from the Greenland and Antarctic Ice Sheets. Between 1901—2010, global mean sea level has increased by around 0.19 [0.17—0.21] metres, based on tide gauge data with satellite data incorporated after 1993.
• The projections for future sea level rise in 2081-2100 compared to 1986-2005 range from 0.26 metres to 0.81 metres. In all scenarios, thermal expansion accounts for the largest individual share, about 30-55 per cent of the total.
• Projections of sea level rise in the 21st Century in the IPCC’s Fifth Assessment Report (AR5) are higher than in the Fourth Assessment Report, principally because the contribution of the ice sheets is included. AR5 concluded that there is currently insufficient evidence to evaluate the probability of specific levels of sea level rise above the likely range.
• Based on current understanding, the only way that sea levels could increase by more than the likely range is if the collapse was initiated of areas of the Antarctic ice sheet resting on the continental shelf but below sea level. There is lack of consensus on the probability of such a collapse and the potential additional contributions to sea level rise cannot be quantified precisely.
• It is virtually certain that global mean sea level rise will continue for many centuries beyond 2100. Sea level rise of between 1-3 metres per degree of warming is expected if the warming is sustained for several millennia.
• The available evidence indicates that global warming above a certain threshold (probably over 2°C but less than 4°C warming since pre-industrial times, and possibly even as low as 1°C) would lead to the near-complete loss of the Greenland Ice-Sheet over a millennium or more, which would cause a global mean sea level rise of approximately 7m.

 
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