“You have stolen my childhood and my dreams with your empty words.”
Climate Action Summit
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When the remnants of Europe’s second summertime heat wave migrated over Greenland in late July, more than half of the ice sheet’s surface started melting for the first time since 2012. A study published Wednesday in Nature shows that mega-melts like that one, which are being amplified by climate change, aren’t just causing Greenland to shed billions of tons of ice. They’re causing the remaining ice to become denser.
“Ice slabs”—solid planks of ice that can span hundreds of square miles and grow to be 50 feet thick—are spreading across the porous, air pocket-filled surface of the Greenland ice sheet as it melts and refreezes more often. From 2001 to 2014, the slabs expanded in area by about 25,000 square miles, forming an impermeable barrier the size of West Virginia that prevents meltwater from trickling down through the ice. Instead, the meltwater becomes runoff that flows overland, eventually making its way out to sea.
As the ice slabs continue to spread, the study’s authors predict more and more of Greenland’s surface will become a “runoff zone,” boosting the ice sheet’s contribution to global sea level rise and, perhaps, causing unexpected changes.
It’s easy to think of Greenland as a solid, impenetrable hunk of ice. But in reality about 80 percent of the ice sheet’s surface is like a snowcone: A dusting of fresh snowfall covers a thick layer of old snow, called firn, that’s slowly being compressed into glacier ice but still contains plenty of air pockets. When the top of this snow cone melts in the summer, liquid water percolates down into the firn, which soaks it up like a 100-foot-thick sponge.
MacFerrin and his colleagues got their first hint that the firn may be losing its absorbency in the spring of 2012, when they were drilling boreholes through the firn in southwest Greenland. They started finding dense, compacted layers of ice in core after core, just below the seasonal snow layer. It was, MacFerrin says, as if a “turtle shell” had formed over the firn.
MacFerrin and his colleagues immediately wondered whether that shell might be preventing meltwater from percolating into the firn.
“That was May of 2012,” MacFerrin says. “And July was this record-breaking melt year, and we got our answer very quickly.”
That summer, for the first time on record, meltwater from this part of Greenland visibly started to flow away as runoff.
Realizing they had witnessed something significant, the researchers set about drilling more cores over a larger region to see how extensive the ice shell was. They discovered that it spanned a transect 25 miles long and was having widespread effects on local hydrology.
Those findings, published in 2016 in Nature Climate Change, were the springboard for the new study. Using radar data from NASA’s IceBridge airborne campaign, as well as ground-based surveys, MacFerrin and his colleagues have now created a first-of-its-kind map of ice slabs across the entire surface of Greenland.
Based on modelling results, the researchers think the shell began to form and spread widely in the early 2000s. As of 2014, it covered some 4 percent of Greenland’s surface, according to the new analysis. Every summer that extensive melting occurs, it gets thicker and spreads inland to colder, higher ground.
“Every handful of years, these big melt summers are doing a number on the firn,” MacFerrin says. “That’s causing this whole process to grow inland pretty quickly.”
Ice slabs have already caused Greenland’s runoff zone to expand by about 26 percent, according to the new study. So far the additional runoff has only added about a millimeter to global sea levels. Greenland now contributes a little under a millimeter per year to rising sea levels, through a combination of icebergs breaking off glaciers and melt occurring at the surface and base of the ice sheet.
But if Greenland’s surface hardens more, runoff could rise dramatically. Under a worst-case scenario where carbon emissions continue to climb until the end of the century, the researchers calculated that ice slab proliferation could add up to 3 inches of sea level rise by 2100, boosting the ice sheet’s overall sea level rise contribution by nearly a third. In both a middle-of-the-road scenario where emissions peak by mid-century and the high emissions one, the amount of runoff from Greenland’s interior roughly doubles by century’s end.
But more runoff is only one potential consequence of the transformation taking place in Greenland’s ice. Kristin Poinar, a glaciologist at the University of Buffalo who wasn’t involved in the study, pointed out that slabs of solid ice aren’t nearly as reflective as bright white snowfall.
“And so, if we start getting these ice slabs forming near the ice sheet’s surface, it could potentially…cause the ice sheet to absorb more solar radiation and warm up,” she says. “And that would create more ice slabs.”
And runoff from ice slabs doesn’t have to flow into the ocean, said Indrani Das, a glaciologist at Columbia University who wasn’t involved in the study. She worries about how it could seep into the large crevasses that exist at lower elevations on the ice sheet. From there, the runoff could, potentially, flow all the way down to bedrock, lubricating the zone where the ice makes contact with it.
“That could make the ice sheet flow faster,” Das says, which could cause glaciers to spill their contents into the ocean more quickly, like ice cream sliding off a piece of cake.
To Poinar, the most significant contribution of the new study is that it will allow scientists to improve their projections of future sea level rise, giving coastal communities the information they need to prepare. At the same time, the study highlights the fact that the more carbon we spew into the atmosphere, the more we’re likely to transform Earth’s northern ice sheet in insidious and unexpected ways. And that could have consequences that are difficult to anticipate.
“We have never observed an ice sheet behaving this way before,” Poinar says. “It’s unprecedented in human scientific history.”
Twelve years is at once an eternity and right around the corner. Just ask any parent watching their kids grow up. So it hits home when a growing chorus of often young voices — from proponents of the Green New Deal to the global Youth Climate Strike — says forcefully that the world has 12 years left to avoid disastrous climate change. This is just the latest dire warning about time running out issued over the past 20 years. But this deadline is different — it’s both entirely wrong, and oh so right.
The idea of a 12-year deadline arose last fall with the release of a special report of the Intergovernmental Panel on Climate Change. The United Nations group of climate scientists from around the world said that if the planet’s governments want to limit global warming to 2.7 degrees Fahrenheit (1.5 degrees Celsius) above preindustrial temperatures, a mere 1 degree Fahrenheit above today’s levels, society will have to reduce its greenhouse gas emissions by about half by 2030, declining further to net zero by around midcentury. The “about” and “around” typically get dropped in translation, rendering the outcome falsely precise, especially in headlines about the report. The Guardian, for example, announced: “We have 12 years to limit climate change catastrophe, warns U.N.”
Now, of course, it would be 11 years.
Technically, this deadline is wrong, not least because it is much too precise. The world won’t end in 2030 if emissions don’t decline. The NASA climate scientist Kate Marvel summed it up perfectly: “Climate change isn’t a cliff we fall off, but a slope we slide down.”
That’s one of the many reasons climate change is such a difficult problem. There’s no obvious stop sign, no simple red line. The reverse is also true: There won’t be a superhero ending to this movie, a point when climate change will have been “solved.” Our children and grandchildren — and theirs — will be managing the impacts of climate change for decades and centuries to come.
Still, the equation is simple: fewer emissions equal a more hospitable climate. Rising average temperatures make extreme heat more likely, hurricanes and storms more intense and threaten fresh water supplies. Climate impacts have already started to hit.
Halving greenhouse gas emissions by 2030 would be a tall order, to say the least. Changes to infrastructure take a long time. Cars on the road today are on average about 12 years old, and a new car sold in 2020 could still be on the road in 2040 or later. Power plants are built to stay in service much longer. There are a few coal-fired electric power plants in the United States that first began operation in the 1950s and are still producing electricity today. The inherent inertia that society is up against makes a climate action deadline of about a decade not just a sensible option, but an imperative.
We need to speed up the transition to clean and efficient transportation, electricity, industry, agriculture and buildings, and also make infrastructure and human systems more resilient. Achieving this requires much more than business as usual. It demands an enormous public and private undertaking of policy commitments, investments and innovation initiatives. Ten to 12 years is close enough to focus minds and attention. It’s far enough to allow for the necessary fundamental, systemic changes to take effect. None of that guarantees success.
For one, there is plenty of climate hurt already built in, regardless of how much emissions are cut this coming decade. Second, emissions reductions aiming to limit global average temperatures to 2.7 to 3.6 degrees Fahrenheit (1.5 or 2ºC) are not assured of success. Even if the world started out along a path to limit temperatures to, say, 3.6ºF, a chance remains that temperatures climb (much) higher. Some of the I.P.C.C.’s latest “2ºC pathways” go up to a 50-50 chance of exceeding that level. That’s a planetary game of chance no one should want to play, and precisely why deep decarbonization needs to go hand-in-hand with strong and equitable resilience efforts. But it’s not too late to reduce emissions — it will never be too late. It’s hard to imagine a world where we will regret having reduced emissions.
Achieving big reductions in emissions in less than a dozen years requires political action now, or at least soon after the next presidential election. Whether it is the Green New Deal, fundamental green tax reform, or a combination of any of the comprehensive climate plans being proposed now — there are plenty of options that could be taken to bend the emissions trajectory toward zero both in the United States and around the world. The young people, like the Swedish teenager Greta Thunberg, speaking on behalf of millions are correct in calling for bold climate action now.
With children, days might last forever, but years fly by. Something similar applies to climate policy. The current days of delay and debates can seem to drag on forever, but the next presidential election is right around the corner, and so is 2030. Concrete, realistic deadlines focus the mind and jump-start action. And jump-start we must.
Gernot Wagner is a clinical associate professor at New York University and the co-author of “Climate Shock.” Constantine Samaras is an associate professor at Carnegie Mellon University, where he is director of the Center for Engineering and Resilience for Climate Adaptation.
The international protest will come ahead of the UN Climate Action Summit.