GFZ German research centre for geo sciences

Seawater expansion caused by ocean warming is stronger than previously thought

Sea level rise caused by thermal expansion is acting twice as strong as the melting ice of Greenlands glaciers. A research team led by the University of Bonn came up with this conclusion. Together with colleagues from the GFZ and the Alfred Wegener Institute in Bremerhaven the scientists from Bonn consolidated the Earth's gravity data of the GRACE satellites and radar height measurements of the sea level by satellite Jason-1 and Jason-2.

28.01.2017: Sea level rise caused by thermal expansion is acting twice as strong as the melting ice of Greenlands glaciers. A research team led by the University of Bonn came up with this conclusion. Together with colleagues from the GFZ and the Alfred Wegener Institute in Bremerhaven the scientists from Bonn consolidated the Earth's gravity data of the GRACE satellites and radar height measurements of the sea level by satellite Jason-1 and Jason-2.

All substances expand by warming. This warming also applies to the body of water of the sea, leading to an increase of sea level. In the past twelve years this effect was almost twice as strong as previously thought. Christoph Dahle, leader of the scientific processing system of GRACE and GRACE-FO at GFZ was responsible for the GRACE data analysis: "An important question was how to separate the portions of sea level rise from one another. The two main units are warming-induced expansion of the water and the water increase in mass by melting glaciers." The latter can be estimated from the gravity data of GRACE that were an important part of the investigations.

A new major result: In very deep ocean regions only a small warming is sufficient to cause a significant rise in sea level. An increase of several millimeters per year in deep-sea areas is not uncommon. So far it was assumed that only about 0.7 to 1.0 millimeters of global sea level rise were caused by thermal expansion of sea water. Now it can be stated that between 2002 and 2014 the warming of the water body accounted for 1.4 millimeters of sea level rise per year. That is pretty much twice as much as the melting of Greenland ice is contributing to sea level change.

R. Rietbroek, S.-E. Brunnabend, J. Kusche, J. Schröter, C. Dahle, 2016. Revisiting the Contemporary Sea Level Budget on Global and Regional Scales. Proceedings of the National Academy of Sciences of the United States of America (PNAS), DOI: 10.1073/pnas.1519132113

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