As the world’s ice sheets have been cracking up and melting down, climatologists have warned that further decimation could cause devastating levels of sea level rise. Now, a recent study shows that ice sheets of Greenland and Antarctica are melting at a pace on par with the worst-case climate scenarios scientists have predicted, putting coastal communities where millions of people reside at risk.
In the study published in Nature Climate Change last week, researchers compared satellite observations of ice melt at the poles with calculations from the models in the Intergovernmental Panel on Climate Change’s (IPCC) 2015 fifth assessment report. The report is considered the gold standard, synthesizing studies from the around the world.
They found that from when satellite record keeping began in the early 1990s to 2017, Greenland and Antarctica lost a combined lost 6.4 trillion metric tons of ice. As a result, global sea levels have risen by 0.7 inches (1.8 centimeters).
But the rate of ice loss has not stayed consistent—it’s been speeding up in recent years. Approximately 0.5 inches (1.2 centimeters) of that sea level rise occurred between 2007 and 2017. The rate seen in that one decade period, the researchers found, lines up almost perfectly with the IPCC’s 2014 report’s worst-case scenario.
“Although we anticipated the ice sheets would lose increasing amounts of ice in response to the warming of the oceans and atmosphere, the rate at which they are melting has accelerated faster than we could have imagined,” said Tom Slater, lead author of the study and climate researcher at the Center for Polar Observation and Modelling at the University of Leeds, in a statement.
If ice loss continues at that rate, the 2014 report’s climate models show that by 2100, ice melt from the two sheets could raise sea levels by roughly another 6.7 inches (17 centimeters). That would double the frequency of dangerous storm-surge flooding in many of the world’s biggest coastal cities, and expose an additional 16 million people to dangerous annual coastal flooding.
“That’s enough to double the frequency of storm-surge flooding in many of the world’s largest coastal cities,” Anna Hogg, study co-author and climate researcher in the School of Earth and Environment at the University of Leeds, said in a statement.
Until recently, the main cause of global sea level rise has been thermal expansion—seawater expanding as it heats up. But over the past five years, the researchers say, ice melt has become the main thing pushing up the world’s oceans. The new research follows an August study which found Antarctica’s ice sheet is becoming vulnerable to quick destruction by melt water seeping into its fractures. And on the other side of the world, research published earlier this year found that sunny skies added to the woes of last year’s record Greenland melt. Plenty of smaller sources of ice are also becoming problematic, from disappearing glaciers in the Alps to Iceland.
Alarmingly, the study authors say that since sea level rise is already meeting scientists’ worst-case projections, the actual worst case could be even more severe. It may require completely reimagining the climate models used to estimate sea level rise.
“Although we anticipated the ice sheets would lose increasing amounts of ice in response to the warming of the oceans and atmosphere, the rate at which they are melting has accelerated faster than we could have imagined,” said Slater. “The melting is overtaking the climate models we use to guide us, and we are in danger of being unprepared for the risks posed by sea level rise.”