Thursday, October 20, 2011

Scientists Estimate Sea level Rise for next 500 years

Rising seas are one of the more long-term catastrophic effects of global warming that will not end at 2100, even with the most drastic emission reductions, but will continue for centuries. Researchers based at the Niels Bohr Institute in Copenhagen have calculated the long-term outlook for the next 500 years for rising sea levels in relation to the emission of greenhouse gases and pollution of the atmosphere using a climate model calibrated against actual historical measurements of sea level rise.

The change in sea levels is driven by massive inertia in the earth's climate system. With anthropogenic global warming melting the Greenland ice sheet and mountain glaciers and warming the oceans, the processes causing sea level rise are now underway and accelerating. Increasing Groundwater extraction for agricultural and mining use is also a small but notable contribution to sea level rise.

Caption: The graph shows how sea levels will change for four different pathways for human development and greenhouse gas pollution. The green, yellow and orange lines correspond to scenarios where it takes 10, 30, or 70 years before emissions are stabilized. The red line can be considered to represent business as usual where greenhouse gas emissions are increasing over time.

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For each metre of sea level rise we will experience on average about 100 metres of coastal inundation.

"Based on the current situation we have projected changes in sea level 500 years into the future. We are not looking at what is happening with the climate, but are focusing exclusively on sea levels", explains Aslak Grinsted, a researcher at the Centre for Ice and Climate, the Niels Bohr Institute at the University of Copenhagen.

The model used for forecasting sea level rise over the next 500 years took into account emission of greenhouse gases and aerosols and the pollution of the atmosphere and was calibrated to actual historic measurements, and then used to predict the outlook for rising sea levels.

Four emissions scenarios were used to calculate possible sea level rise. With the most pessimistic scenario emissions will continue to rise resulting in 1.1 meter rise by the year 2100 and 5.5 meters by the year 2500.

The two more realistic scenarios, based upon global action on stabilizing emissions and carbon pollution, resulted in a sea level rise of about 75 cm by 2100 and 2 meters of sea level rise by 2500.

In the most optimistic scenario where drastic action is taken globally to cut emissions through strong climate change goals, the sea would continue to rise reaching about 60 cm by 2100 and 1.8 meters by the year 2500.

"Most rise is expected after stabilization of forcing, due to the long response time of sea level. For all scenarios the rate of sea level rise would be positive for many centuries, requiring 200–400 years to drop to the 1.8 mm/yr 20th century average." says the research abstract.

As you can see there is incredible inertia in turning around sea level rise due to climate change. The rate of sea level change is likely to continue for two to 4 centuries, even if we reduce emissions and stabilize atmospheric CO2 today.

"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", says Aslak Grinsted.

Even with the uncertainties of long-term calculations, the inertia in the melting of the ice sheets and warming of the oceans will cause a likely rise of 75 cm by the year 2100 and by the year 2500 the sea will have risen by about 2 meters, according to the study.

The research was conducted by S. Jevrejevaa, J.C. Moore, and A. Grinstede and was published in the scientific journal Global and Planetary Change.

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