Rise in sea level from ice melt in Greenland and Antarctica match worst-case scenario: study

About a year ago, water and climate expert Bob Sandford flew over Greenland at a moment he says was historic, both scientifically and climatically — the island recorded the most ice melt, about 11.3 billions tonnes, in a single day since recording began in the 1950s.

"It's an understatement to say that what I saw left me really quite devastated," Sandford said. He's the chair in water and climate security at the United Nations University Institute for Water, Environment and Health.

Now, according to a recent study, lead by Thomas Slater, a climate researcher at the Centre for Polar Observation and Modelling at the University of Leeds, those rapidly melting ice sheets in Greenland, along with melting ice sheets in Antarctica are thought to be the main contributor to a rise in sea levels around the world. And the rate of the melt matches the UN's Intergovernmental Panel on Climate Change's worst-case climate warming scenario.

The study was co-authored by Anna Hogg, climate researcher with the University of Leeds in England, and Ruth Mottram, a climate researcher at the Danish Meteorological Institute.

The researchers compared the latest results from satellite surveys from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) — an international scientific collaboration of estimates of the ice sheet contribution to sea level rise — with calculations from climate models.

It shows that since the 1990s, melting ice sheets have raised the global sea level by 1.8 centimetres, but the latest measurements show that the world's oceans are now rising by four millimetres each year.

While it may not sound like a lot, if this rate continues, sea levels could rise another 17 centimetres and could expose 16 million people to annual coastal flooding by the end of the century, the study found.

"Ice is being lost and it's being lost at an accelerating rate. And this is causing sea level rise around the world," said Hogg. "I think what we show in our research and what's supported by other literature as well is that even very incremental gradual sea level rise can have really big impacts on flooding around our coastlines."

For years, sea level rise was mainly driven by thermal expansion — the swell of water particles as it gets warmer.

However, the study says that over the last five years, melting ice sheets and glaciers has overtaken that.

Not surprising, says ice caps researcher

Alison Criscitiello, the director of the Canadian Ice Core Lab at the University of Alberta and a researcher on ice caps in the Antarctic and Canadian High Arctic, said in an email to CBC that she isn't surprised by the study's results.

"Even so, reading the results of this new study did make my stomach sink," she said.

"The implications are profound; the risks posed by future sea level rise may be of a scale we simply are unprepared for. The speed at which ice melt contributions have overtaken thermal expansion contributions to sea level rise should alarm everyone on this planet."

Sandford, with the UN institute, says the Arctic is warming up three to five times faster than the global average.

As well, he said climate change and the impacts in the Arctic and the world's high mountain ranges are occurring decades before they were projected. For example, he says that the scale of the record loss of ice melt in August 2019, had not been projected to occur until somewhere around 2070.

Sandford added if anything, the numbers reported in the study regarding the number of people affected by coastal flooding could be conservative.

"We can surmise from this that the changes humanity has made to the composition of the global atmosphere are not just going to be severe, they're going to be sudden," he said, adding Greenland has warmed six degrees in the last 60 years.

"I was forced to, by what I saw with my own eyes, face the realization that abrupt climate change is not just a possibility. It's an absolute."

New research is 'accurate representation': researcher

Mike MacFerrin, postdoctoral research associate in the Earth Science and Observation Center at the University of Colorado Boulder, says that 30 or more years ago, the primary consensus was that huge ice sheets, which took millennia to slowly build, could only collapse slowly after millennia of melt.

But most people now have dropped that belief, MacFerrin said.

"The ice sheets are highly dynamic, complex systems with triggers and threshold behaviours that can only be resolved with the best models we have. It's an exciting time to be an ice sheet scientist, while at the same time a terrifying time to be an informed global citizen."

MacFerrin says the new research is "an accurate representation of the best evidence we have."

While there are multiple competing studies that argue about the magnitude and future of melt processes — such as some studies that show evidence that mitigating factors may cause ice losses to at least partially taper off — MacFerrin says all the research helps.

"Reality will tell us how the balance of all these processes play out for global sea levels into 2100," MacFerrin said.

"At least so far, the runaway processes — the 'bad ones'— are winning out and the ice sheets are doing their best simulations of worst-case melt scenarios. That's what this paper points out."