Worst case sea-level rise now very likely

 From Inside Climate News

From the polar caps to the glaciers of Europe, Asia and South America, global warming is melting the planet’s ice faster than ever and speeding the inundation of the world’s coastlines.

New research shows the annual melt rate grew from 0.8 trillion tons in the 1990s to 1.3 trillion tons by 2017, and has accelerated most in the places with the most ice—the Greenland and Antarctic ice shelves and sheets.

Those massive systems of land and sea-based ice are melting as fast as the worst-case climate scenarios in major global climate reports, said Thomas Slater, a co-author of the new study in The Cryosphere that measured the meltdown from 1994 to 2017, which covers a timespan when every decade was warmer than the previous one and also includes the 20 warmest years on record.

It’s one of the first studies to gather estimates for all the planet’s ice, except permafrost. Previous research has typically focused on single elements of the cryosphere, like glaciers, sea ice or ice shelves, said Ruth Mottram, a climate scientist with the Danish Meteorological Institute, who was not involved in the new study.

Slater said that evaluating the data didn’t numb him to the staggering amount of ice that melted during the study period, describing it as a mountain towering higher than Mount Everest and covering Manhattan—enough to raise global sea level 1.4 inches in 23 years.

“The ice sheets are now following the worst-case climate warming scenarios set out by the Intergovernmental Panel on Climate Change,” he said. “Sea-level rise on this scale will have very serious impacts on coastal communities this century.” 

Sea level has gone up about eight or nine inches since 1880. It’s likely to rise at least 12 inches, and could rise by as much as 8.2 feet by 2100, according to recent estimates by the National Oceanic and Atmospheric Administration. The Intergovernmental Panel on Climate Change estimates a rise of between two and three feet by 2100 if global warming is kept well below two degrees Celsius (3.6 degrees Fahrenheit), or three to five feet if temperatures rise past that.

Getting the projections right is critical because, by some estimates, every centimeter of sea level rise threatens to displace about 1 million people from low-lying towns and croplands. For cities near sea level, knowing whether the ocean will rise two feet or five feet is literally a billion dollar question, and in worse case scenarios, a matter of survival and dislocation.

Various studies show an “acceleration in sea level rise the last five years or so, from about 1.2 inches per decade, to a rate of 1.9 inches per decade,” Mottram said. “We know it does vary a lot from year to year and things like El Niño, or if Greenland has a warm summer, can have an effect. But the deeper ocean is also getting warmer and that continues to add thermal expansion too. So sea level rise will continue for centuries.”

The Jökulsárlón glacial lake is seen in Iceland in 2015. New research shows that Earth's ice is melting faster than ever. The annual melt rate grew from 0.8 trillion tons in the 1990s to 1.3 trillion tons by 2017. Credit: Bob Berwyn