New study finds that the pace of sea level rise has nearly tripled since 1990


Glaciers_and_Icebergs_at_Cape_York
Icebergs are breaking off glaciers at Cape York, Greenland. (Wikimedia)
Jake Slobe | May 24, 2017

Scientists, in a new study, have found that the Earth’s oceans are rising nearly three times as quickly as they were throughout most of the 20th century.

This new finding  is one of the strongest indications yet that a much feared trend of not just sea level rise, but its acceleration, is now underway.

Their paper, published in the Proceedings of the National Academy of Sciences, isn’t the first to find that the rate of rising seas is itself increasing — but it finds a bigger rate of increase than in past studies. The new paper concludes that before 1990, oceans were rising at about 1.1 millimeters per year, or just 0.43 inches per decade. From 1993 through 2012, though, it finds that they rose at 3.1 millimeters per year, or 1.22 inches per decade.

Studying the changing rate of sea level rise is complicated by the fact that scientists only have a precise satellite record of its rate going back to the early 1990s. Before that, the records rely on tide gauges spread around the world in various locations.

But sea level rise varies widely in different places, due to the rising and sinking of land, large-scale gravitational effects on the waters of the globe and other local factors. So scientists have struggled to piece together a longer record that merges together what we know from satellites with these older sources of information.

The new study takes a crack at this problem by trying to piece together a sea level record for the 20th century, before the beginning of the satellite record, by adjusting the results of local tide gauges based on an understanding of the factors affecting sea level rise in a given region, and then also weighting different regions differently in the final analysis. That’s how it came up with a relatively small rate of sea level rise from 1900 through 1990, followed by a much faster one afterward.

 

That 2015 study found that from 1901 to 1990, sea level rose at a rate of 1.2 millimeters per year, very close to the current study’s estimate. But other researchers have found figures more in the range of 1.6 to 1.9 millimeters.

 Overall, though, the disparities between different studies — many of which point to an acceleration, but which vary upon its size — suggests that scientists have converged on the big picture but are still debating the details.

Just how much control we are able to exert over the rate of sea level rise will critically depend on how rapidly global greenhouse gas emissions come down in coming years — making the entire outlook closely tied to whether the United States sticks with the rest of the world in honoring the Paris climate agreement.

 

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