High tides would creep higher, slowly burying every shoreline on the planet, flooding coastal cities and creating hundreds of millions of climate refugees. All this could play out in a mere 20 to 50 years — much too quickly for humanity to adapt.
Six feet of sea level rise is more likely than three feet. But if carbon emissions continue to track on something resembling a worst-case scenario, the full 11 feet of ice locked in West Antarctica might be freed up, their study showed…
Another recent study indicates that Pine Island’s glaciers shattered in a relatively short amount of time at the end of the last ice age.
A fast transition away from fossil fuels in the next few decades could be enough to put off rapid sea-level rise for centuries. That’s a decision worth countless trillions of dollars and millions of lives.
….Land-based ice, …when it falls into the ocean, it adds to the overall volume of liquid in the seas. Thus, sea-level rise. Antarctica is a giant landmass — about half the size of Africa — and the ice that covers it averages more than a mile thick. Before human burning of fossil fuels triggered global warming, the continent’s ice was in relative balance: The snows in the interior of the continent roughly matched the icebergs that broke away from glaciers at its edges.
Now, as carbon dioxide traps more heat in the atmosphere and warms the planet, the scales have tipped.
A wholesale collapse of Pine Island and Thwaites would set off a catastrophe. Giant icebergs would stream away from Antarctica like a parade of frozen soldiers. All over the world, high tides would creep higher, slowly burying every shoreline on the planet, flooding coastal cities and creating hundreds of millions of climate refugees.
All this could play out in a mere 20 to 50 years — much too quickly for humanity to adapt.
…A study they published last year was the first to incorporate the latest understanding of marine ice-cliff instability into a continent-scale model of Antarctica. Their results drove estimates for how high the seas could rise this century sharply higher. “Antarctic model raises prospect of unstoppable ice collapse,” read the headline in the scientific journal Nature, a publication not known for hyperbole.
Instead of a three-foot increase in ocean levels by the end of the century, six feet was more likely, according to DeConto and Pollard’s findings. But if carbon emissions continue to track on something resembling a worst-case scenario, the full 11 feet of ice locked in West Antarctica might be freed up, their study showed….
…At six feet, though, around 12 million people in the United States would be displaced, and the world’s most vulnerable megacities, like Shanghai, Mumbai, and Ho Chi Minh City, could be wiped off the map.
At 11 feet, land currently inhabited by hundreds of millions of people worldwide would wind up underwater.South Florida would be largely uninhabitable; floods on the scale of Hurricane Sandy would strike twice a month in New York and New Jersey, as the tug of the moon alone would be enough to send tidewaters into homes and buildings…
In a new study out last month in the journal Nature, a team of scientists from Cambridge and Sweden point to evidence from thousands of scratches left by ancient icebergs on the ocean floor, indicating that Pine Island’s glaciers shattered in a relatively short amount of time at the end of the last ice age….
…“Every revision to our understanding has said that ice sheets can change faster than we thought,” he says. “We didn’t predict that Pine Island was going to retreat, we didn’t predict that Larsen B was going to disintegrate. We tend to look at these things after they’ve happened.”
There’s a recurring theme throughout these scientists’ findings in Antarctica: What we do now will determine how quickly Pine Island and Thwaites collapse. A fast transition away from fossil fuels in the next few decades could be enough to put off rapid sea-level rise for centuries. That’s a decision worth countless trillions of dollars and millions of lives. “The range of outcomes,” Bassis says, “is really going to depend on choices that people make.”
Totten Glacier, the largest glacier in East Antarctica, is being melted from below by warm water that reaches the ice when winds over the ocean are strong, according to research. The new findings are a cause for concern because the glacier holds more than 11 feet of sea level rise and acts as a plug that helps lock in the ice of the East Antarctic Ice Sheet.
Chad A. Greene, Donald D. Blankenship, David E. Gwyther, Alessandro Silvano, Esmee van Wijk. Wind causes Totten Ice Shelf melt and acceleration. Science Advances, 2017; 3 (11): e1701681 DOI: 10.1126/sciadv.1701681
Central parts of Antarctica’s ice sheet have been stable for millions of years, from a time when conditions were considerably warmer than now, research suggests…Although the discovery demonstrates the long-term stability of some parts of Antarctica’s ice sheet, scientists remain concerned that ice at its coastline is vulnerable to rising temperatures….
…”These findings help us understand how the Antarctic Ice Sheet has evolved, and to fine-tune our models and predict its future. The preservation of old rock surfaces is testimony to the stability of at least the central parts of the Antarctic Ice Sheet — but we are still very concerned over other parts of Antarctica amid climate change.”…
David E. Sugden, Andrew S. Hein, John Woodward, Shasta M. Marrero, Ángel Rodés, Stuart A. Dunning, Finlay M. Stuart, Stewart P.H.T. Freeman, Kate Winter, Matthew J. Westoby. The million-year evolution of the glacial trimline in the southernmost Ellsworth Mountains, Antarctica. Earth and Planetary Science Letters, 2017; 469: 42 DOI: 10.1016/j.epsl.2017.04.006
Scientists have known for decades that small changes in climate can have significant impacts on the massive Antarctic Ice Sheet. Now a new study suggests the opposite also is true. An international team of researchers has concluded that the Antarctic Ice Sheet actually plays a major role in regional and global climate variability — a discovery that may also help explain why sea ice in the Southern Hemisphere has been increasing despite the warming of the rest of the Earth.
Results of the study are being published this week in the journal Nature….”What we discovered, however, is that the ice sheet has undergone numerous pulses of variability that have had a cascading effect on the entire climate system.”
….”The introduction of that cold, fresh water lessens the salinity and cools the surface temperatures, at the same time, stratifying the layers of water,” Clark said. “The cold, fresh water freezes more easily, creating additional sea ice despite warmer temperatures that are down hundreds of meters below the surface.” The discovery may help explain why sea ice has expanded in the Southern Ocean despite global warming, the researchers say
…The Antarctic Ice Sheet covers an area of more than 5 million square miles and is estimated to hold some 60 percent of all the fresh water on Earth. The east part of the ice sheet rests on a major land mass, but in West Antarctica, the ice sheet rests on bedrock that extends into the ocean at depths of more than 2,500 meters, or more than 8,000 feet, making it vulnerable to disintegration.
Scientists estimate that if the entire Antarctic Ice Sheet were to melt, global sea levels would rise some 200 feet…
Pepijn Bakker, Peter U. Clark, Nicholas R. Golledge, Andreas Schmittner, Michael E. Weber. Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge. Nature, 2016; DOI: 10.1038/nature20582
Scientists have found evidence in a chunk of bedrock drilled from nearly two miles below the summit of the Greenland ice sheet that the sheet nearly disappeared for an extended time in the last million years or so. The finding casts doubt on assumptions that Greenland has been relatively stable during the recent geological past, and implies that global warming could tip it into decline more precipitously than previously thought.
First-of-their-kind studies provide new insight into the deep history of the Greenland Ice Sheet, looking back millions of years farther than previous techniques allowed. However, the two studies present some strongly contrasting evidence about how Greenland’s ice sheet may have responded to past climate change.
New research by an international team shows that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s.
…The team concluded the date at which the grounding line retreated from a prominent seafloor ridge was in 1945 at the latest. The team also found that final ungrounding of the ice shelf from the ridge occurred in 1970.
“Our results suggest that, even when climate forcing (such as El Niños, which create warmer water) weakened, ice-sheet retreat continued,” said James Smith of the British Antarctic Survey and lead author of an article appearing in the Nov. 23 issue of the journal, Nature.
The West Antarctic Ice Sheet is one of the largest potential sources of water that will contribute to rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line — which marks the boundary between grounded ice and floating ice shelf — is under way….
….The appearance of plutonium in the sediment marks the onset of above-ground testing of nuclear weapons in the 1950s, and indicates that ice-sheet retreat began before this time…..”Despite a return to pre-1940s climatic conditions in the ensuing decades, thinning and glacier retreat has not stopped and is unlikely to be reversible without a major change in marine or glaciological conditions,” Smith said. “A period of warming in the Antarctic shelf waters triggered a substantial change in the ice sheet, via the mechanism that we see today — that is, ocean-driven thinning and retreat of ice shelves leads to inland glacier acceleration and ice-sheet thinning.”
J. A. Smith, et al. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier. Nature, 2016; DOI: 10.1038/nature20136
Experts agree that a new era for climate policy here. But the hard work starts now.
The Paris climate agreement, first struck in December 2015, enters into force today. The treaty commits countries worldwide to keep carbon emissions “well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C”.
Countries will pursue self-determined emissions targets, agreed upon before the last round of climate talks, from 2020 onwards. The national targets will be reviewed and strengthened every five years.
The agreement also commits richer countries to provide funding to poorer countries, which have done the least to contribute to climate change but will suffer its worst effects.
As the world embarks on its most dedicated effort yet to prevent catastrophic climate change, The Conversation asked a panel of international experts to give their view on the significance of the agreement coming into force.
Stefan Rahmstorf: Governments should be in emergency mode
The Paris Agreement is the best we could have expected at this point in history. It is a beacon of hope. Almost all nations on Earth have decided to move towards net zero emissions.
It was high time, and in some respects too late. Paris came almost exactly 50 years after the famous Revelle report from the US president’s scientific advisory panel issued a stark warning of global warming, melting ice caps and rising seas due to our carbon dioxide emissions.
The long delay in confronting this threat is not least a result of a major, still ongoing obfuscation campaign by fossil fuel interests.
Two degrees would be very likely to destabilise the West Antarctic ice sheet (evidence is mounting that this has already happened). Such an increase might even destabilise the Greenland ice sheet and parts of the East Antarctic ice sheet, locking in more than ten metres of sea-level rise and sealing the fate of coastal cities and island nations.
Some major impacts of our fossil fuel burning cannot be prevented now, thanks to the fateful delays already mentioned. But every 0.1°C of warming we avoid helps contain further massive risks to humanity, including major threats to food security.
Because of all the time that was lost, the remaining emissions budget is very tight: at current rate, we are eating up the budget to stay below 1.5°C (with a 50:50 chance) in about ten years. The budget for 2°C would allow us to keep emitting for about 30 years. If we ramp down emissions rapidly we can stretch these budgets out to last longer, but the key here is to turn the tide of emissions now or we can give up on staying well below 2°C.
If we take the Paris Agreement seriously (and we should), governments around the world should be in emergency mode, taking rapid and decisive measures to get their emissions down.