Sea Levels To Rise For Thousands Of Years
03 October 3, 2012
Greenhouse gas emissions up to now have triggered an irreversible warming of the Earth that will cause sea levels to rise for thousands of years to come, finds a new research .
The results come from a study, report of which has been published on October 2, 2012 in IOP Publishing's journal Environmental Research Letters . The researchers are from Vrije Universiteit Brussel, Manchester Metropolitan University and the Université catholique de Louvain .
The study sought to model sea-level changes over millennial timescales, taking into account all of Earth's land ice and the warming of the oceans -- something which has not been done before.
The research showed that we have already committed ourselves to a sea-level rise of 1.1 meters by the year 3000 as a result of our greenhouse gas emissions up to now. This irreversible damage could be worse, depending on the route we take to mitigating our emissions.
If we were to follow the high A2 emissions scenario adopted by the Intergovernmental Panel on Climate Change (IPCC), a sea-level rise of 6.8 meters could be expected in the next thousand years. The two other IPCC scenarios analyzed by the researchers, the B1 and A1B scenarios, yielded sea-level rises of 2.1 and 4.1 meters respectively.
"Ice sheets are very slow components in the climate system; they respond on time scales of thousands of years," said Professor Philippe Huybrechts, co-author of the study.
"Together with the long life-time of greenhouse gases in the atmosphere, this inertia is the real poison on the climate system: anything we do now that changes the forcing in the climate system will necessarily have long consequences for the ice sheets and sea level."
Professor Huybrechts continued: "Ultimately the current polar ice sheets store about 65 meters of equivalent sea level and if climatic warming will be severe and long-lasting all ice will eventually melt.
"Mankind should limit the concentration of greenhouse gases at the lowest possible level as soon as possible. The only realistic option is a drastic reduction of the emissions. The lower the ultimate warming will be, the less severe the ultimate consequences will be."
In all of the scenarios that the researchers analyzed, the Greenland ice sheet was responsible for more than half of the sea level rises; thermal expansion of the oceans was the second highest contributor, and the contribution of glaciers and ice was only small.
The researchers perceive this is the first study to include glaciers, ice caps, the Greenland and Antarctic ice sheets and the thermal expansion of the oceans into a projection of sea-level rises.
They did so by using a climate modeling system called LOVECLIM, which includes components from a number of different subsystems.
The polar ice sheets are not normally included into projections due to computational constraints, whilst researchers often find it difficult to account for the 200 000 individual glaciers that are found all over the world in very different climatic settings.
It should be mentioned that almost one year ago another study  made broadly similar warning. The difference was related to time period: 500 years.
A team of researchers including researchers from the Niels Bohr Institute calculated the long-term outlook for rising sea levels in relation to the emission of GHGs and pollution of the atmosphere using climate models. The results were published in the scientific journal Global and Planetary Change .
"Based on the current situation we have projected changes in sea level 500 years into the future," explained Aslak Grinsted, a researcher at the Centre for Ice and Climate, the Niels Bohr Institute at the University of Copenhagen .
The researchers made calculations for four scenarios: a pessimistic one, an optimistic one, and two more realistic ones.
In the pessimistic scenario, emissions continue to increase. This will mean that sea levels will rise 1.1 meters by the year 2100 and will have risen 5.5 meters by the year 2500.
Even in the most optimistic scenario, which requires extremely dramatic climate change goals, major technological advances and strong international cooperation to stop emitting GHGs and polluting the atmosphere, the sea would continue to rise. By the year 2100 it will have risen by 60 cm and by the year 2500 the rise in sea level will be 1.8 meters.
For the two more realistic scenarios, calculation based on the emissions and pollution stabilizing, the results showed that there will be a sea level rise of about 75 cm by the year 2100 and that by the year 2500 the sea will have risen by 2 meters.
"In the 20th century sea has risen by an average of 2mm per year, but it is accelerating and over the last decades the rise in sea level has gone approximately 70% faster. Even if we stabilize the concentrations in the atmosphere and stop emitting greenhouse gases into the atmosphere, we can see that the rise in sea level will continue to accelerate for several centuries because of the sea and ice caps long reaction time. So it would be 2-400 years before we returned to the 20th century level of a 2 mm rise per year," said Aslak Grinsted.
 ScienceDaily , “Irreversible Warming Will Cause Sea Levels to Rise for Thousands of Years to Come, New Research Shows”, Oct. 2, 2012, http://www.sciencedaily.com/releases/2012/10/121001191531.htm
H Goelzer, P Huybrechts, S C B Raper, M-F Loutre, H Goosse, T Fichefet. Millennial total sea-level commitments projected with the Earth system model of intermediate complexity LOVECLIM. Environmental Research Letters, 2012; 7 (4): 045401 DOI: 10.1088/1748-9326/7/4/045401 Institute of Physics (2012, October 2)
 ScienceDaily , “Sea Levels to Continue to Rise for 500 Years? Long-Term Climate Calculations Suggest So”, Oct. 17, 2011 http://www.sciencedaily.com/releases/2011/10/111017102601.htm
S. Jevrejeva, J.C. Moore, A. Grinsted. Sea level projections to AD2500 with a new generation of climate change scenarios. Global and Planetary Change, 2011; DOI: 10.1016/j.gloplacha.2011.09.006
University of Copenhagen (2011, October 17)
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