Global Ice Loss on Pace to Drive Worst-Case Sea Level Rise

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.

Sea Level Rise is a Matter of Life and Death

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.

Mottram said the new findings don’t necessarily mean that global sea level will continue to track the most dire predictions because there are other factors involved, mainly the expansion of the oceans as they warm, which until recently accounted for most of the sea level rise that’s been measured.

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,” she 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.”

Analyzing glacial and polar ice melt at the same time helps distinguish how much of the melting is caused by atmospheric warming compared to ocean heat. The atmosphere reacts relatively quickly to changes in its concentrations of greenhouse gases, which warm the Earth, and other pollutants that can reflect heat away from the planet. Oceans respond much more slowly to the drivers of global warming. Understanding those dynamics sharpens projections of sea level rise, he said.

University of Liége ice researcher Xavier Fettweis, who was not involved in the research, said the findings help reduce the uncertainties around ice melt and sea level rise by adding new information from satellites to update the datasets used in previous studies. 

It covers a key period for the planet’s climate because the big surge in polar ice melting started during the 1990s, “likely because we have exceeded the temperature threshold of 0 degrees Celsius (32 degrees Fahrenheit) over large areas. The cryosphere is starting to change as soon as this temperature threshold is reached,” he said. Climate models looking back to 1950 robustly show there was “no significant and durable change in melt,” before the 1990s.

The Numbers are Huge and Scary

However you measure it, the global ice loss numbers add up to trouble, said glaciologist Heïdi Sevestre, who was not involved with the study. 

The numbers are “becoming so huge and so astronomical, what more do we need to act?” she asked. “We need to understand the human cost and the economic cost of every ton of ice. I think if we knew the true cost of every ton of ice that’s lost, if people knew this, we’d stop immediately.” 

Sevestre worries that policymakers are seeing the accelerating melting of the world’s ice as an opportunity rather than a threat.

“Last week I had a chance to speak to the French decision-makers, and they see the Arctic as a big pie they want to get a piece of, the fisheries and energy,” she said. “They believe it’s going to be an Eldorado for fisheries, but as we lose sea ice and the Arctic Ocean becomes more acidic, that’s definitely not going to happen.”

In her presentation to the decision-makers, she emphasized that a worst-case sea level rise means that “we’re going to lose the main French harbor, and we’re going to lose the cold water from glaciers that we need to cool our nuclear power plants.”

“There have been so many studies about ice loss and sea level rise that it’s easy to get numbed by the numbers,” she said. “But, of course, they should never feel normal, and the fact that climate change is accelerating should never feel normal.”

The new research is another warning that warming beyond 1.5 degrees Celsius (2.7 degrees Fahrenheit) will push the world’s ice past a tipping point, leading to irreversible melting and destabilization of ice sheets, she said.

“We should act as quickly as we can to prevent going beyond these thresholds,” Sevestre said. “We’re in uncharted territory. We can’t afford to lose one more ton of ice. We don’t have any other options.”