The tangible effects of global warming are already evident around the world, contributing to droughts that fueled forest fires in southern Europe and exacerbating hurricanes that devastated the Caribbean this summer.
But the impact of rising waters in the long term could be far more damaging.
Global sea levels are expected to increase anywhere between 0.66 to 6.6 feet (0.2 meters to 2 meters) by the end of this century, according to NASA, threatening many of the world’s coastal cities.
Surface melt area
Maximum surface melt extent
Source: Thomas Mote and Kyle Mattingly, University of Georgia
Areas losing most ice
Height change in meters of water equivalent since 2002
Source: NASA-JPL/Caltech
If the ice sheet covering Greenland was to melt completely — a process scientists believe could take several hundred years at the current rate — sea levels could rise by as much as 24 feet (about 7 meters).
And surface melt on Greenland’s ice sheet has been accelerating, spurred by soaring temperatures in the Arctic, which is warming twice as fast as the rest of the planet.
In 2017, after two decades of decline, less summer thawing and heavy snowfall spurred by low pressure systems meant Greenland didn’t lose as much ice as in recent years.
But 2017 was an anomaly. Greenland’s overall ice loss has increased dramatically in the last two decades — from shedding an average of 34 gigatons (or 34 billion metric tons) per year between 1992 and 2001 to about 280 gigatons annually since 2002.
Average annual ice loss
In gigatons
Source: NASA
That’s enough meltwater for every person on the planet to drink 107 liters of water ...
... every day of the year.
Much of the melt is occurring at several “hot spots,” where glaciers flow into the sea.
Helheim Glacier is the fastest flowing glacier along Greenland’s eastern edge. Scientists are studying it in hopes of improving projections of future sea level rise.
Helheim's retreat
Glacier's calving front (September of selected years)
Source: ESA. Image: Landsat (1990)
Helheim — named after the “realm of the dead” in Norse mythology — is retreating rapidly.
For years the glacier moved at a relatively stable speed, but between 2000 and 2005, it seemed to be collapsing into the sea. Since then, its front has partially recovered, but it’s still losing ice, spurred by warmer air and waters.
Between August 2016 and August 2017, New York University researchers David and Denise Holland say Helheim retreated a whopping two miles — the largest one-year loss they’ve witnessed in a decade.
Climatologist Jason Box says there are hundreds of glaciers in Greenland like Helheim, and many of them have doubled in speed.
Jason Box isn’t the only one stunned by Greenland’s quickly shifting landscape. For those who call the island home, the melting ice sheet is changing centuries of tradition.
Like his father and grandfather before him, Tobias Ignatiussen has been hunting with his dogs since he was a boy.
But today there’s much less ice for dog-sledding, and the 56-year-old worries that his children will grow up in a very different Greenland to the one he remembers.
Box and some other leading climate scientists agree that Earth is already locked into at least 3.2 feet (1 meter) of global sea level rise by the end of this century — a projection that even drastic cuts in carbon dioxide emissions won’t reverse.
This could be disastrous for many of the world’s coastal cities — from Miami to Mumbai and New York City to Shanghai — and the people who call them home.
But scientists have stressed that as oceans rise, they won’t do so evenly. Because ice sheets are so huge, changes in their mass will affect Earth’s gravity and rotation, determining how meltwater is distributed.
Counterintuitively, that means that sea levels closest to melting land ice may actually drop, shielding places like Reykjavik, Iceland from being inundated.
Researchers from NASA’s Jet Propulsion Laboratory recently released a study that takes those variables into account — pinpointing how melting glaciers may someday flood coastal cities around the world.