NCAR scientist John Fasullo is a co-author of a new study appearing in the Proceedings of the National Academies of Science. The study finds that the rate of sea level rise is accelerating. The following is an excerpt from a news release by the Cooperative Institute for Research in Environmental Sciences. 

February 13, 2018 | Global sea level rise is not cruising along at a steady 3 mm per year. It’s accelerating a little every year, according to a new study that harnessed 25 years of satellite data to calculate that the rate is increasing by about 0.08 mm/year every year — which could mean an annual rate of sea level rise of 10 mm/year, or even more, by 2100.

“This acceleration, driven mainly by accelerated melting in Greenland and Antarctica, has the potential to double the total sea level rise by 2100 as compared to projections that assume a constant rate—to more than 60 cm instead of about 30.” said lead author Steve Nerem, a scientists at the Cooperative Institute for Research in Environmental Sciences. "And this is almost certainly a conservative estimate," he added. "Our extrapolation assumes that sea level continues to change in the future as it has over the last 25 years. Given the large changes we are seeing in the ice sheets today, that's not likely."

If the oceans continue to change at this pace, sea level will rise 65cm (26 inches) by 2100—enough to cause significant problems for coastal cities, according to the new assessment by Nerem and several colleagues from CU Boulder, the University of South Florida, NASA Goddard Space Flight Center, Old Dominion University, and the National Center for Atmospheric Research. The team, driven to understand and better predict Earth’s response to a warming world, published their work today in the journal Proceedings of the National Academy of Sciences.

Rising concentrations of greenhouse gases in Earth’s atmosphere increase the temperature of air and water, which causes sea level to rise in two ways. First, warmer water expands, and this "thermal expansion" of the oceans has contributed about half of the 7 cm of global mean sea level rise we've seen over the last 25 years, Nerem said. Second, melting land ice flows into the ocean, also increasing sea level across the globe.

These increases were measured using satellite altimeter measurements since 1992, including the U.S./European TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3 satellite missions. But detecting acceleration is challenging, even in such a long record. Episodes like volcanic eruptions can create variability: the eruption of Mount Pinatubo in 1991 decreased global mean sea level just before the Topex/Poseidon satellite launch, for example. In addition, global sea level can fluctuate due to climate patterns such as El Niños and La Niñas (the opposing phases of the El Niño Southern Oscillation, or ENSO) which influence ocean temperature and global precipitation patterns.

Read the full news release here. 

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