The Reversibility of Sea Level Rise

• Published in: Journal of climate Vol. 26; no. 8; pp. 2502 - 2513
• Main Authors: Bouttes, N., Gregory, J. M., Lowe, J. A.
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 15.04.2013
• Subjects: Air temperature; Carbon; Carbon dioxide; Carbon dioxide concentration; Carbon dioxide emissions; Climate; Climate change; Climate models; Climatology. Bioclimatology. Climate change; Earth Sciences; Earth, ocean, space; Emissions; Emissions control; Energy balance; Exact sciences and technology; External geophysics; General circulation models; Geoengineering; Global climate; Global warming; Heat; Ice sheets; Marine; Mean sea level; Meteorology; Mitigation; Ocean temperature; Ocean warming; Ocean, Atmosphere; Oceanography; Oceans; Physics of the oceans; Radiative forcing; Sciences of the Universe; Sea level; Sea level changes; Sea level rise; Seawater; Simulation; Step response; Surface temperature; Surface waves, tides and sea level. Seiches; Surface-air temperature relationships; Thermal expansion; Vertical profiles; Thermal expansion; global change; climate warming; Reversibility; Sea level rise; Impact study; ocean-atmosphere interaction; sea level; climate change
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/JCLI-D-12-00285.1

During the last century, global climate has been warming, and projections indicate that such a warming is likely to continue over coming decades. Most of the extra heat is stored in the ocean, resulting in thermal expansion of seawater and global mean sea level rise. Previous studies have shown that after CO₂ emissions cease or CO₂ concentration is stabilized, global mean surface air temperature stabilizes or decreases slowly, but sea level continues to rise. Using idealized CO₂ scenario simulations with a hierarchy of models including an AOGCM and a step-response model, the authors show how the evolution of thermal expansion can be interpreted in terms of the climate energy balance and the vertical profile of ocean warming. Whereas surface temperature depends on cumulative CO₂ emissions, sea level rise due to thermal expansion depends on the time profile of emissions. Sea level rise is smaller for later emissions, implying that targets to limit sea level rise would need to refer to the rate of emissions, not only to the time integral. Thermal expansion is in principle reversible, but to halt or reverse it quickly requires the radiative forcing to be reduced substantially, which is possible on centennial time scales only by geoengineering. If it could be done, the results indicate that heat would leave the ocean more readily than it entered, but even if thermal expansion were returned to zero, the geographical pattern of sea level would be altered. Therefore, despite any aggressive CO₂ mitigation, regional sea level change is inevitable.