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.
“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
Dr.-Ing. Roelof Rietbroek
Institute of Geodesy and Geoinformation
University of Bonn
http://store.pangaea.de/Publications/RietbroekR-etal_2015/Sealevel_pnasRietbroek... Google Earth can also be used to visualize some of the results available here
Johannes Seiler | idw - Informationsdienst Wissenschaft
Greenland ice flow likely to speed up: New data assert glaciers move over sediment, which gets more slippery as it gets wetter
17.08.2017 | Swansea University
Climate change: In their old age, trees still accumulate large quantities of carbon
17.08.2017 | Universität Hamburg
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
18.08.2017 | Life Sciences
18.08.2017 | Physics and Astronomy
18.08.2017 | Materials Sciences