Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Climate Change: Ocean Warming Underestimated


To date, research on the effects of climate change has underestimated the contribution of seawater expansion to sea level rise due to warming of the oceans. A team of researchers at the University of Bonn has now investigated, using satellite data, that this effect was almost twice as large over the past twelve years than previously assumed. That may result in, for example, significantly increased risks of storm surges. The scientists are presenting their findings in the renowned scientific journal “Proceedings of the National Academy of Sciences of the United States of America” (PNAS).

In principle, water in the oceans acts like a mercury thermometer: when the temperature goes up, the liquid expands and climbs up the little tube. Since the world’s oceans are similarly locked in between the continents, their levels also rise when they heat up due to rising temperatures.

Dr.-Ing. Roelof Rietbroek from the Institute for Geodesy and Geoinformation at the University of Bonn, with a global illustration of the rise in sea levels on his computer monitor.

© Photo: Johannes Seiler/Uni Bonn

“In the deeper parts of the ocean, even a small amount of warming is enough to create a significant rise in sea level,” says Dr.-Ing. Roelof Rietbroek from the Institute of Geodesy and Geoinformation at the University of Bonn. An increase of several millimeters a year, he says, is not rare in deep-sea zones.

“To date, we have underestimated how much the heat-related expansion of the water mass in the oceans contributes to a global rise in sea level,” says Dr. Jürgen Kusche, Professor of Astronomical, Physical and Mathematical Geodesy at the University of Bonn.

Together with researchers at the Deutsches GeoForschungsZentrum (GFZ) in Potsdam and the Alfred Wegener Institute (AWI) in Bremerhaven, the geodesists used gravity field data from the GRACE satellites and sea-level measurements from the altimeters on Jason-1 and Jason-2 to calculate how much sea levels had risen, both due to warming-related expansion of the water and due to the increase of ocean mass from 2002 to 2014.

Effect is twice as large as the melting ice masses in Greenland

Until now, it was assumed that sea levels rose an average of 0.7 to 1.0 millimeters a year due to this “thermometer effect.” According to the new calculations, however, the ocean’s expansion contributed with about 1.4 millimeters a year – in other words, almost twice as much as previously assumed. “This height difference corresponds to roughly twice the volume from the melting ice sheets in Greenland,” says Dr. Rietbroek.

In addition, the sea-level rise varies strongly due to volume expansion in various ocean regions along with other effects. According to the research team’s calculations, the Philippines hold the record with about 15 millimeters a year, while the levels are largely stable on the West Coast of the United States – because there is hardly any ocean warming in that region.

Risk of storm surges could increase significantly

The main areas threatened by rising sea levels are coastal settlements, where regional changes can play a greater role than the global increase. “No country will raise its levees because of a couple of millimeters,” says Dr. Rietbroek. “But these small amounts add up to several centimeters within decades. Under such conditions, the likelihood of a destructive storm surge could increase dramatically.” From the perspective of the research team, it is thus worth keeping an eye on the expansion-related sea-level rise in the world’s oceans in light of climate change. Little measurement data is available, they say, to show how much the oceans are warming up and expanding at depths of thousands of meters in conjunction with rising global air temperatures.

“Up to now, the physical expansion processes in the deep sea have been considered only to a limited extent,” says the geodesy researcher from the University of Bonn. However, he says, they play a key role in estimating the climate effects. Therefore it would be highly interesting to observe future heat-related expansion of the world’s oceans, using new satellite missions, and to reinterpret measurement data from the past. A longer observation period will help show what proportion of the rise in sea level is due to human activity, and what proportion is due to natural causes. Dr. Rietbroek: “In addition, the estimated trend in sea level is much less affected by natural fluctuations compared to the observed trend in global temperatures, so it is a more reliable indicator of climate change.”

Publication: 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

Media contact:

Dr.-Ing. Roelof Rietbroek
Institute of Geodesy and Geoinformation
University of Bonn
Tel. ++49-228-733577
Twitter: @r_rietje

Weitere Informationen: Google Earth can also be used to visualize some of the results available here

Johannes Seiler | idw - Informationsdienst Wissenschaft
Further information:

Further reports about: Climate Friedrich-Wilhelms-Universität levels oceans sea level

More articles from Earth Sciences:

nachricht Jacobs University supports new mapping of Mars, Mercury and the Moon
21.03.2018 | Jacobs University Bremen gGmbH

nachricht Thawing permafrost produces more methane than expected
20.03.2018 | GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

TRAPPIST-1 planets provide clues to the nature of habitable worlds

21.03.2018 | Physics and Astronomy

The search for dark matter widens

21.03.2018 | Materials Sciences

Natural enemies reduce pesticide use

21.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>