Sea levels are rising at faster clip as polar melt accelerates, new study shows

By Joby Warrick
11 May 2015 (Washington Post) – Global sea levels are climbing at a faster rate than previously thought, according to a new analysis that underscores scientists’ concerns about the impact of melting glaciers and ice sheets near the Earth’s poles. The new research published Monday in the journal Nature Climate Change shows that the rate of sea-level rise appears to have accelerated over the past 15 years, a period in which scientists elsewhere documented a surprisingly rapidly retreat of some of Earth’s great ice masses, from Greenland to West Antarctica. The findings appear to contradict earlier studies suggesting that the rate of sea-level rise had actually slowed slightly in recent years. Australian scientists detected the increase in a study that analyzed decades of records from tidal gauges around the world, together with satellite data that show changes in water levels as well as subtle shifts in land formations. Using these more precise measurements, the researchers discovered that scientists had slightly overstated sea-level rise that occurred in the 1990s, and underestimated the rate of increase since 1999, said Christopher Watson, a University of Tasmania geodesist who co-authored the study along with colleagues from the university and from Australia’s national science agency, the Commonwealth Scientific and Industrial Research Organization. The adjusted figures showed ocean levels rising over the past two decades at a rate of between 2.6 and 2.9 millimeters a year — or just over a tenth of an inch, he said. That rate is consistent with the projections of the Intergovernmental Panel on Climate Change, the U.N.-sponsored scientific body regarded as the internationally accepted authority on global warming. “The acceleration is also consistent with what we expect, given the increasing contributions from the West Antarctic and Greenland ice sheets,” Watson said in an e-mail. [more]

ABSTRACT: The rate of global mean sea-level (GMSL) rise has been suggested to be lower for the past decade compared with the preceding decade as a result of natural variability1, with an average rate of rise since 1993 of +3.2 ± 0.4 mm yr−1 (refs 2, 3). However, satellite-based GMSL estimates do not include an allowance for potential instrumental drifts (bias drift4, 5). Here, we report improved bias drift estimates for individual altimeter missions from a refined estimation approach that incorporates new Global Positioning System (GPS) estimates of vertical land movement (VLM). In contrast to previous results (for example, refs 6, 7), we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied. These rates are in closer agreement with the rate derived from the sum of the observed contributions2, GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied (updated from ref. 8) and reprocessed ERS-2/Envisat altimetry9. Second, in contrast to the previously reported slowing in the rate during the past two decades1, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections2, 10, and larger than the twentieth-century acceleration2, 8, 10.