Global sea level rise isn’t just happening — it’s happening much faster than previously thought, according to new research from climate scientists at the University of Tasmania, in Australia.
The study, published Monday in Nature Climate Change, found that sea level rise has been speeding up over the past two decades compared to the rest of the 20th century. This contradicts previous satellite data dating back to 1993, which appeared to show sea level rise accelerating in the 1990s, but slowing slightly over the past decade.
“That slowing has puzzled scientists because it coincides with an increase in water entering our oceans from Greenland and West Antarctica,” Christopher Watson, the study’s lead author, said in a press statement.
To understand the apparent slowdown in sea level rise, researchers at the University of Tasmania looked at other factors that might impact sea level measurement, such as changes in the height of the Earth’s land surface. First, Watson and his colleagues compared data from tide gauges — which measure sea level height relative to a specific set of coordinates — to satellite data, which measures the height of the sea surface using radar.
Data collected from tide gauges can be skewed by things like earthquakes or sediment settling, which can change where the tide gauge is located relative to the coordinate points it’s measuring. That change in location can affect the gauge’s measurement of sea level. To account for these issues, Watson and his colleagues used GPS stations to understand how tide gauges have risen or fallen — where no GPS stations existed, they used computer modeling to estimate how the tide gauges might have changed position.
Using the newly recalibrated data, the researchers found that sea level rise between 1993 and 1999 — the earliest segment of satellite data — was overstated. According to satellite data, over that six-year period, global sea level rose 3.2 milimeters (about .12 inches) per year; using Watson’s recalibrated data, sea levels probably rose closer to between 2.6 to 2.9 mm (about .1 to .11 inches) per year. This over-estimation of sea level rise gave the appearance of sea level rise slowing in the previous decade, when it was actually accelerating at a rate of between 0.041 and 0.058 mm (.001 to .002 inches) per year.
“We see acceleration, and what I find striking about that is the fact that it’s consistent with the projections of sea level rise published by the IPCC,” Watson told the Guardian. “Sea level rise is getting faster. We know it’s been getting faster over the last two decades than its been over the 20th century and its getting faster again.”
Because sea levels can naturally fluctuate as water is exchanged between land and sea, Watson notes that the rate of increase is too small to be statistically significant — though he told the Washington Post that it’s clear that sea levels are now rising at roughly double the rate observed in the 20th century, something that will have potentially huge ramifications for coastal areas across the world.
“Accelerating sea level is a massive issue for the coastal zone — the once-in-a-lifetime inundation events will become far more frequent, and adaptation will need to occur,” Watson told the Post. “Agencies need to fully consider the impact of accelerating sea level and plan accordingly.”