The most complete assessment to date of Antarctica’s ice sheets confirms that the meltdown accelerated sharply in the past five years, and there is no sign of a slowdown.
That means sea level is expected to rise at a rate that will catch some coastal communities unprepared despite persistent warnings, according to the international team of scientists publishing a series of related studies this week in the journal Nature.
The scientists found that the rate of ice loss over the past five years had tripled compared to the previous two decades, suggesting an additional 6 inches of sea level rise from Antarctica alone by 2100, on top of the 2 feet already projected from all sources, including Greenland.
That may not sound like a lot, but it’s a big deal for people living along coasts,” said University of Leeds climate researcher Andrew Shepherd, who led the assessment, supported by NASA and the European Space Agency. “And the signals are not abating. The ice shelves continue to retreat, warmer ocean water continues to melt them from below, which all means we are progressively going to lose more and more ice from the interior.”
Coastal flooding is already becoming an increasing problem in U.S. cities as sea level rises. A study released last week by the National Oceanic and Atmospheric Administration found that the frequency of high-tide flooding had doubled in the past 30 years, with some cities experiencing more than 20 days of it over the past year….
Abstract: The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). Over this period, ocean-driven melting has caused rates of ice loss from West Antarctica to increase from 53 ± 29 billion to 159 ± 26 billion tonnes per year; ice-shelf collapse has increased the rate of ice loss from the Antarctic Peninsula from 7 ± 13 billion to 33 ± 16 billion tonnes per year. We find large variations in and among model estimates of surface mass balance and glacial isostatic adjustment for East Antarctica, with its average rate of mass gain over the period 1992–2017 (5 ± 46 billion tonnes per year) being the least certain.
Emissions of one of the chemicals most responsible for the Antarctic ozone hole are on the rise, despite an international treaty that required an end to its production in 2010, a new study shows.
Trichlorofluoromethane, or CFC-11, is the second-most abundant ozone-depleting gas in the atmosphere and a member of the family of chemicals most responsible for the giant hole in the ozone layer that forms over Antarctica each September. Once widely used as a foaming agent, production of CFC-11 was phased out by the Montreal Protocol in 2010.
…These findings represent the first time emissions of one of the three most abundant, long-lived CFCs have increased for a sustained period since production controls took effect in the late 1980s.
If the source of these emissions can be identified and mitigated soon, the damage to the ozone layer should be minor. If not remedied soon, however, substantial delays in ozone layer recovery could be expected, Montzka said….
Stephen A. Montzka et al. An unexpected and persistent increase in global emissions of ozone-depleting CFC-11. Nature, 2018; 557 (7705): 413 DOI: 10.1038/s41586-018-0106-2
Glacial meltwater makes the ocean’s surface layer less salty and more buoyant, preventing deep mixing in winter and allowing warm water at depth to retain its heat and further melt glaciers from below.
A further increase in the supply of glacial meltwater to the waters around the Antarctic shelf may trigger a transition from a cold regime to a warm regime, characterised by high rates of melting from the base of ice shelves and reduced formation of cold bottom waters that support ocean uptake of atmospheric heat and carbon dioxide.
A new study has revealed a previously undocumented process where melting glacial ice sheets change the ocean in a way that further accelerates the rate of ice melt and sea level rise. The research found that glacial meltwater makes the ocean’s surface layer less salty and more buoyant, preventing deep mixing in winter and allowing warm water at depth to retain its heat and further melt glaciers from below.
….”This process is similar to what happens when you put oil and water in a container, with the oil floating on top because it’s lighter and less dense,” Mr Silvano said. “The same happens near Antarctica with fresh glacial meltwater, which stays above the warmer and saltier ocean water, insulating the warm water from the cold Antarctic atmosphere and allowing it to cause further glacial melting.
“We found that in this way increased glacial meltwater can cause a positive feedback, driving further melt of ice shelves and hence an increase in sea level rise.” The study found that fresh meltwater also reduces the formation and sinking of dense water in some regions around Antarctica, slowing ocean circulation which takes up and stores heat and carbon dioxide. “The cold glacial meltwaters flowing from the Antarctic cause a slowing of the currents which enable the ocean to draw down carbon dioxide and heat from the atmosphere.
“In combination, the two processes we identified feed off each other to further accelerate climate change.”…
Alessandro Silvano, Stephen Rich Rintoul, Beatriz Peña-Molino, William Richard Hobbs, Esmee van Wijk, Shigeru Aoki, Takeshi Tamura, Guy Darvall Williams. Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water. Science Advances, 2018; 4 (4): eaap9467 DOI: 10.1126/sciadv.aap9467
The grounding line, where the glaciers become floating ice shelves, is receding as much as 600 feet per year, bolstering fears of a worst-case Antarctic meltdown scenario, with global sea level rising 10 feet by 2100.
Eight of the frozen continent’s 65 major ice streams had retreated by more than 410 feet per year—five times the average rate of retreat since the end of the last ice age. The grounding line of some of the glaciers emptying into the Amundsen Sea had retreated by up to 600 feet per year.
A new analysis of satellite data has found “extreme” changes underway at eight of Antarctica’s major glaciers, as unusually warm ocean water slips in under their ice shelves. The warmer water is eating away at the glaciers’ icy grasp on the seafloor. As a result, the grounding line—where the ice last touches bedrock—has been receding by as much as 600 feet per year, a new study shows. Behind the grounding line, the land-based ice then speeds up, increasing the rate of sea level rise.
The new continent-wide measurements of grounding lines suggests a widespread pattern of melting all around Antarctica, said University of Leeds climate researcher Hannes Konrad, lead author of the analysis published today in the scientific journal Nature Geoscience….
….Eight of the frozen continent’s 65 major ice streams had retreated by more than 410 feet per year—five times the average rate of retreat since the end of the last ice age. The grounding line of some of the glaciers emptying into the Amundsen Sea had retreated by up to 600 feet per year.
…Climate models suggest that the current rate of retreat could lead to “centennial-scale collapse of the inland catchment areas,” the study says. That suggests that huge areas of ice far from the ocean could collapse within 100 years, leading to unexpected pulses of sea level rise.
The land-based ice can also speed up in response to ice shelf thinning more than 500 miles away, according to a new study by British and German climate scientists who showed that the effects of localized ice shelf thinning can reach across the entire shelf. Konrad said those findings help show where Antarctica is most vulnerable to future ocean warming, including the large Ross and Filchner-Ronne ice shelves….
Each 5-year delay – a peak in 2025 instead of 2020, for example – most likely adds 20 cm of sea level rise by 2300, and could potentially add a full meter due to the uncertainty associated with the large ice sheets
A new study published in Nature looks at how much global sea level will continue to rise even if we manage to meet the Paris climate target of staying below 2°C hotter than pre-industrial temperatures. The issue is that sea levels keep rising for several hundred years after we stabilize temperatures, largely due to the continued melting of ice sheets in Antarctica and Greenland from the heat already in the climate system.
The study considered two scenarios. In the first, human carbon pollution peaks somewhere between 2020 and 2035 and falls quickly thereafter, reaching zero between 2035 and 2055 and staying there. Global temperatures in the first scenario peak at and remain steady below 2°C. In the second scenario, we capture and sequester carbon to reach net negative emissions (more captured than emitted) between 2040 and 2060, resulting in falling global temperatures in the second half of the century….
…The study also shows that it’s critical that our carbon pollution peaks soon. Each 5-year delay – a peak in 2025 instead of 2020, for example – most likely adds 20 cm of sea level rise by 2300, and could potentially add a full meter due to the uncertainty associated with the large ice sheets…
…Another new study, published in the Proceedings of the National Academy of Sciences, found that sea level rise has been accelerating. If the rate of acceleration continues – which the lead author notes is a conservative estimate – we would see an additional 65 cm (close to a meter above pre-industrial sea level) of sea level rise by 2100.
Penguins preserve records of Antarctic environmental change. The birds’ feathers and eggshells contain the chemical fingerprints of variations in diet, food web structure and even climate, researchers reported February 12 at the American Geophysical Union’s 2018 Ocean Sciences Meeting.
The Antarctic environment has changed dramatically in recent decades. Overfishing has led to a decline in krill, small swimming crustaceans that are a key food source for birds, whales, fish and penguins in the Southern Ocean. Climate change is altering wind directions, creating open water regions in the sea ice that become hot spots for life….
…This study highlights the power of this amino acid isotope technique to track environmental change through animal tissues, says Seth Newsome, an animal ecologist at the University of New Mexico in Albuquerque who was not involved in the study. The technique is becoming popular because it can detect both diet and baseline changes in the food web from the same tissue, he says.
“This 80-year record is just part of a much broader record of change,” McMahon said.
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.”
Measurements from satellites this year showed the hole in Earth’s ozone layer that forms over Antarctica each September was the smallest observed since 1988, scientists have announced…
….The ozone hole over Antarctica is expected to gradually become less severe as chlorofluorocarbons — chlorine-containing synthetic compounds once frequently used as refrigerants — continue to decline. Scientists expect the Antarctic ozone hole to recover back to 1980 levels around 2070.
Ozone is a molecule composed of three oxygen atoms that occurs naturally in small amounts. In the stratosphere, roughly 7 to 25 miles above Earth’s surface, the ozone layer acts like sunscreen, shielding the planet from potentially harmful ultraviolet radiation that can cause skin cancer and cataracts, suppress immune systems and also damage plants. Closer to the ground, ozone can also be created by photochemical reactions between the sun and pollution from vehicle emissions and other sources, forming harmful smog.
Although warmer-than-average stratospheric weather conditions have reduced ozone depletion during the past two years, the current ozone hole area is still large compared to the 1980s, when the depletion of the ozone layer above Antarctica was first detected. This is because levels of ozone-depleting substances like chlorine and bromine remain high enough to produce significant ozone loss.
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
The new rift in Larsen C emerged days after a Delaware-sized iceberg broke off from the ice shelf.
Scientists aren’t totally sure of the implications, but it seems the ice shelf isn’t quite done breaking apart yet.
The same team of British scientists who announced last week’s birth of the humongous iceberg spotted the crack in high-resolution satellite data. The scientists noted the crack “may result in further ice shelf loss” in a blog post published Wednesday. The huge iceberg itself has already begun to break apart.
Ice shelves are floating extensions of glaciers, so their breakup has virtually no effect on global sea levels. The worry is the new rift is heading in the general direction of the Bawden Ice Rise, which is “a crucial point of stabilization for Larsen C Ice Shelf,” according to the British team. A destabilized Larsen C could speed up the flow of its parent glaciers to the ocean, which would have a slight effect on sea levels.…