A new study has warned that ice sheets in Greenland and Antarctica are melting at a rate that matches the worst case scenario developed by the Intergovernmental Panel on Climate Change.
Global sea levels have already risen by 1.8 metres since the 1990s. If they continue to rise at their current pace of 4mm per year, 16 million people worldwide could be affected by an increase in coastal flooding by the end of this century, according to researchers.
The study, by scientists at the Danish Meteorological Institute and the University of Leeds, compared the latest satellite surveys of ice sheet mass with past climate models that tried to predict how fast the ice sheets would melt.
Dr Tom Slater, the study’s lead author and a climate researcher at the Centre for Polar Observation and Modelling at the University of Leeds, said the ice sheet melting “has accelerated faster than we could have imagined”.
"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,” he said.
Dr Anna Hogg, a co-author of the study and a climate researcher at the School of Earth and Environment at Leeds, said: "If ice sheet losses continue to track our worst-case climate warming scenarios, we should expect an additional 17cm of sea level rise from the ice sheets alone [by the end of this century]. That's enough to double the frequency of storm-surge flooding in many of the world's largest coastal cities."
Historically, sea levels have mostly risen because of a process called thermal expansion, where the volume of sea water expands the warmer it gets. However, over the last five years, the melting of ice sheets – and the subsequent volume of water that adds to oceans – has overtaken thermal expansion as the leading cause of rising sea levels.
Ruth Mottram, climate researcher at the Danish Meteorological Institute, said: “It is not only Antarctica and Greenland that are causing the water to rise. In recent years, thousands of smaller glaciers have begun to melt or disappear altogether, as we saw with the glacier Ok in Iceland, which was declared ‘dead’ in 2014. This means that melting of ice has now taken over as the main contributor of sea level rise.”
While neither situation is expected, if all the ice sheets in Antarctica were to melt, that would cause sea levels to rise by 58 metres; in Greenland, the same scenario would cause a rise of just over seven metres.