Rising sea levels are a problem. Perhaps not so much for those living in land-locked areas, but the results can be devastating for coastal communities. Scientists are aware that global warming trends cause ice at the poles to melt, where they drain into the sea. The question, however, has always been of how fast it’s happening. Now, according to new data from researchers at the University of Tasmania that correct earlier estimates, sea levels have actually risen faster in the last 20 years than previously believed.
“Unlike the previous slowing, an estimate of acceleration is striking in that it is consistent with the projections of future sea level published by the Intergovernmental Panel on Climate Change,” said Dr Christopher Watson from the University’s School of Land and Food.
Sea level is a notoriously difficult thing to measure, particularly on a global scale. The earliest methods relied on data from tidal gauges on land, which aren’t incredibly accurate – natural phenomena can cause landforms to change, after all. Under those current estimates, the thinking goes that sea levels rose rapidly in the 1990s, but recent years have seen a slower, somewhat abated rise.
That’s not the case, according to Dr Watson and his colleagues. By analyzing decades of records from tidal gauges alongside more modern satellite records, Watson found that earlier readings actually overestimated the sea level rise in the 1990s, which is the good news. The bad news is that scientists also underestimated the rate at which it’s risen since about 1999 – what seemed like a slowed rate of sea level rise was actually a distortion of data caused by the earlier overestimation.
“Previously, it was clear that the rate of rise over the past 20 years was roughly double the rate determined over the past century – what was curious was that the rate appeared slower in the last decade relative to the one before,” said Dr Watson. “That slowing has puzzled scientists because it coincides with an increase in water entering our oceans from Greenland and West Antarctica.”
Due to the earlier mishandling of the data, the overall rate of sea level rise from 1993-2014 is a bit lower than believed: Anywhere from 2.6-2.9mm per year as opposed to the earlier estimate of 3.2 mm per year. Still, that value is difficult to pinpoint thanks to changes in land motion. There’s also evidence that the rate has increased in the satellite era (since 1993), but year over year changes in sea level are hard to estimate due to water exchanged between land and sea in events like floods.
“The acceleration is also consistent with what we expect, given the increasing contributions from the West Antarctic and Greenland ice sheets,” Watson told the Washington Post in an e-mail.
Scientists estimate that if greenhouse gasses remain unchecked, sea levels could rise nearly 100cm by 2100. Even with a stringent plan for greenhouse gas abatement, the rise is still projected at between 28 and 61cm.
“Rising sea levels will place increasing stress on the coastal zone – inundation events will become more frequent and adaptation will need to occur,” Dr Watson said. “Agencies need to consider the impacts of accelerating sea levels and provide communities with advice and planning directions that are commensurate with the magnitude of the problem.”
If nothing changes, at least our landlocked friends may be able to more easily enjoy beaches several generations from now.