A chunk of floating ice that weighs more than a trillion metric tons broke away from the Antarctic Peninsula, producing one of the largest icebergs ever recorded and providing a glimpse of how the Antarctic ice sheet might ultimately start to fall apart.
….Larsen C, like two smaller ice shelves that collapsed before it, was holding back relatively little land ice, and it is not expected to contribute much to the rise of the sea. But in other parts of Antarctica, similar shelves are holding back enormous amounts of ice, and scientists fear that their future collapse could dump enough ice into the ocean to raise the sea level by many feet. How fast this could happen is unclear.
In the late 20th century, the Antarctic Peninsula, which juts out from the main body of Antarctica and points toward South America, was one of the fastest-warming places in the world. That warming had slowed or perhaps reversed slightly in the 21st century, but scientists believe the ice is still catching up to the higher temperatures….
A one trillion tonne iceberg — one of the biggest ever recorded — has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice finally completed its path through the ice…. Whilst this new iceberg will not immediately raise sea levels, if the shelf loses much more of its area, it could result in glaciers that flow off the land behind speeding up their passage towards the ocean. This non-floating ice would have an eventual impact on sea levels, but only at a very modest rate.
….In the Antarctic summer of 2016, the surface of the Ross Ice Shelf, the largest floating ice platform on Earth, developed a sheet of meltwater that lasted for as long as 15 days in some places. The total area affected by melt was 300,000 square miles, or larger than the state of Texas, the scientists report.
That’s bad news because surface melting could work hand in hand with an already documented trend of ocean-driven melting to compromise West Antarctica, which contains over 10 feet of potential sea level rise.
“It provides us with a possible glimpse of the future,” said David Bromwich, an Antarctic expert at Ohio State University and one of the study’s authors. The paper appeared in Nature Communications.
“You probably have read these analyses of West Antarctica, many people think it’s slowly disintegrating right now, and it’s mostly thought to be from the warm water eating away at the bottom of critical ice shelves,” Bromwich continued. “Well, that’s today. In the future, we could see action at the surface of these ice shelves as well from surface melting. So that makes them potentially much more unstable.”…
Abstract: Over the past two decades the primary driver of mass loss from the West Antarctic Ice Sheet (WAIS) has been warm ocean water underneath coastal ice shelves, not a warmer atmosphere. Yet, surface melt occurs sporadically over low-lying areas of the WAIS and is not fully understood. Here we report on an episode of extensive and prolonged surface melting observed in the Ross Sea sector of the WAIS in January 2016. A comprehensive cloud and radiation experiment at the WAIS ice divide, downwind of the melt region, provided detailed insight into the physical processes at play during the event. The unusual extent and duration of the melting are linked to strong and sustained advection of warm marine air toward the area, likely favoured by the concurrent strong El Niño event. The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major melt events.
Antarctic Dispatches is a three-part series from the seventh continent. Written by Justin Gillis. We went to Antarctica to understand how changes to its vast ice sheet might affect the world. New York Times.
The acceleration is making some scientists fear that Antarctica’s ice sheet may have entered the early stages of an unstoppable disintegration….
Because the collapse of vulnerable parts of the ice sheet could raise the sea level dramatically, the continued existence of the world’s great coastal cities — Miami, New York, Shanghai and many more — is tied to Antarctica’s fate….
Remote as Antarctica may seem, every person in the world who gets into a car, eats a steak or boards an airplane is contributing to the emissions that put the frozen continent at risk. If those emissions continue unchecked and the world is allowed to heat up enough, scientists have no doubt that large parts of Antarctica will melt into the sea.
But they do not know exactly what the trigger temperature might be, or whether the recent acceleration of the ice means that Earth has already reached it. The question confronting society, said Richard B. Alley, a climate scientist at Pennsylvania State University, is easier to ask than to answer: “How hot is too hot?”…
More than 60 percent of the freshwater on Earth is locked in Antarctica’s ice sheets. Parts of the West Antarctic ice sheet are rapidly losing ice into the sea. See graphics: Red areas have lost 10 feet or more of ice since 2010. Blue areas have gained ice. …
The risk is clear: Antarctica’s collapse has the potential to inundate coastal cities across the globe.
Over tens of millions of years, thin layers of snow falling on the continent — in many places, just a light dusting every year — were pressed into ice, burying mountain ranges and building an ice sheet more than two miles thick. Under its own weight, that ice flows downhill in slow-moving streams that eventually drop icebergs into the sea.
If that ice sheet were to disintegrate, it could raise the level of the sea by more than 160 feet — a potential apocalypse, depending on exactly how fast it happened. Recent research suggests that if society burns all the fossil fuels known to exist, the collapse of the ice sheet will become inevitable.
Improbable as such a large rise might sound, something similar may have already happened, and recently enough that it is still lodged in collective memory.
In the 19th century, ethnographers realized that virtually every old civilization had some kind of flood myth in its literature.
In the Epic of Gilgamesh, waters so overwhelm the mortals that the gods grow frightened, too. In India’s version, Lord Vishnu warns a man to take refuge in a boat, carrying seeds. In the Bible, God orders Noah to carry two of every living creature on his ark.
“I don’t think the biblical deluge is just a fairy tale,” said Terence J. Hughes, a retired University of Maine glaciologist living in South Dakota. “I think some kind of major flood happened all over the world, and it left an indelible imprint on the collective memory of mankind that got preserved in these stories.”
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
1 Scientific understanding of sea-level rise is advancing at a rapid pace. Projections of future sea-level rise, especially under high emissions scenarios, have increased substantially over the last few years, primarily due to new and improved understanding of mass loss from continental ice sheets. These sea-level rise projections will continue to change as scientific understanding increases and as the impacts of local, state, national and global policy choices become manifest. New processes that allow for rapid incorporation of new scientific data and results into policy will enable state and local agencies to proactively prepare.
2 The direction of sea level change is clear.Coastal California is already experiencing the early impacts of a rising sea level, including more extensive coastal flooding during storms, periodic tidal flooding, and increased coastal erosion.
3 The rate of ice loss from the Greenland and Antarctic Ice Sheets is increasing.These ice sheets will soon become the primary contributor to global sea-level rise, overtaking the contributions from ocean thermal expansion and melting mountain glaciers and ice caps. Ice loss from Antarctica, and especially from West Antarctica, causes higher sea-level rise in California than the global average: for example, if the loss of West Antarctic ice were to cause global sea-level to rise by 1 foot, the associated sea-level rise in California would be about 1.25 feet…
4 New scientific evidence has highlighted the potential for extreme sea-level rise. If greenhouse gas emissions continue unabated, key glaciological processes could cross thresholds that lead to rapidly accelerating and effectively irreversible ice loss. Aggressive reductions in greenhouse gas emissions may substantially reduce but do not eliminate the risk to California of extreme sea-level rise from Antarctic ice loss.
5 Probabilities of specific sea-level increases can inform decisions. A probabilistic approach to sea-level rise projections, combined with a clear articulation of the implications of uncertainty and the decision-support needs of affected stakeholders, is the most appropriate approach for use in a policy setting….. These projections may underestimate the likelihood of extreme sea-level rise, particularly under high emissions scenarios, so this report also includes an extreme scenario called the H++ scenario. The probability of this scenario is currently unknown, but its consideration is important, particularly for high-stakes, long-term decisions.
6 Current policy decisions are shaping our coastal future. Before 2050, differences in sea-level rise projections under different emissions scenarios are minor but they diverge significantly past mid-century. After 2050, sea-level rise projections increasingly depend on the trajectory of greenhouse gas emissions. For example, under the extreme H++ scenario rapid ice sheet loss on Antarctica could drive rates of sea-level rise in California above 50mm/year (2 inches/year) by the end of the century, leading to potential sea-level rise exceeding 10 feet. This rate of sea-level rise would be about 30-40 times faster than the sea-level rise experienced over the last century.
7 Waiting for scientific certainty is neither a safe nor prudent option. High confidence in projections of sea-level rise over the next three decades can inform preparedness efforts, adaptation actions and hazard mitigation undertaken today, and prevent much greater losses than will occur if action is not taken. Consideration of high and even extreme sea levels in decisions with implications past 2050 is needed to safeguard the people and resources of coastal California.
In the first such continent-wide survey, scientists have found extensive drainages of meltwater flowing over parts of Antarctica’s ice during the brief summer. Many of the newly mapped drainages are not new, but the fact they exist at all is significant; they appear to proliferate with small upswings in temperature, so warming projected for this century could quickly magnify their influence on sea level. An accompanying study looks at how such systems might influence the great ice shelves ringing the continent, which some researchers fear could collapse, bringing catastrophic sea-level rises. Both studies appear this week in the leading scientific journal Nature.
Jonathan Kingslake, Jeremy C. Ely, Indrani Das, Robin E. Bell. Widespread movement of meltwater onto and across Antarctic ice shelves. Nature, 2017; 544 (7650): 349 DOI: 10.1038/nature22049
Robin E. Bell, Winnie Chu, Jonathan Kingslake, Indrani Das, Marco Tedesco, Kirsty J. Tinto, Christopher J. Zappa, Massimo Frezzotti, Alexandra Boghosian, Won Sang Lee. Antarctic ice shelf potentially stabilized by export of meltwater in surface river. Nature, 2017; 544 (7650): 344 DOI: 10.1038/nature22048
The first-ever hydrological survey of Antarctica has just been completed, and it found nearly 700 streams, ponds, and waterfalls, a sprawling and active meltwater drainage system never previously documented.
….Willis is, in fact, engaged in a project to measure how ice shelves respond to pooling water. He and two other researchers recently spent months in Antarctica, embedding GPS units in different aspects of an ice shelf in order to sense how it torques and flexes as meltwater moves across its surface. “If that water is simply evacuated, then it could be that those ice shelves are more stable than the models currently suggest,” he told me. “But it’s still pretty speculative.”
It’s also unclear how this research will ultimately feed sea-level models. Disintegrating ice shelves threaten to raise global oceans not because of the water they contain, but because they speed up the movement of the glaciers behind them, which are “grounded” on the Antarctic continent. If those ice floes speed up their drive to the sea, they could quickly juice sea levels.
But even if Antarctic ice shelves wind up looking more stable, estimates of sea-level rise before 2100 are unlikely to change. Most near-term sea-level rise will come from “valley glaciers” (ice on the other six continents), thermal expansion (the ocean’s tendency to enlarge as it absorbs heat), and the rapidly eroding ice sheets of Greenland.
Wednesday’s study shows how much there is still to be learned about the southernmost continent—and how much can still be extracted from what we already know. As part of her research, Bell later traveled to Cambridge to read the original Campbell party journals….
The Arctic sea ice maximum extent and Antarctic minimum extent are both record lows this year. Combined, sea ice numbers are at their lowest point since satellites began to continuously measure sea ice in 1979.…”There’s a lot of year-to-year variability in both Arctic and Antarctic sea ice, but overall, until last year, the trends in the Antarctic for every single month were toward more sea ice,” said Claire Parkinson, a senior sea ice researcher at Goddard. “Last year was stunningly different, with prominent sea ice decreases in the Antarctic. To think that now the Antarctic sea ice extent is actually reaching a record minimum, that’s definitely of interest
Arctic sea ice hit a record low wintertime maximum extent in 2017. At 5.57 million square miles, it is the lowest maximum extent in the satellite record, and 455,600 square miles below the 1981 to 2010 average maximum extent.
Credit: NASA Goddard’s Scientific Visualization Studio/L. Perkins
The World Meteorological Organization announced today new verified record high- temperatures in Antarctica, ranging from the high 60s (in Fahrenheit) to the high teens, depending on the location they were recorded in Antarctica. Knowledge and verification of such extremes are important in the study of weather patterns, climate variability and human induced change, report scientists….
…”The polar regions of our planet have been termed the ‘canary’ in our global environment,” Cerveny said. “Because of their sensitivity to climate changes, sometimes the first influences of changes in our global environment can be seen in the north and south polar regions. Knowledge of the weather extremes in these locations therefore becomes particularly important to the entire world. The more we know of this critically important area to our environment, the more we can understand how all of our global environments are interlinked.”…
Scientists are eyeing a growing crack in one of Antarctica’s ice shelves. A portion of the Larcen C shelf the size of Delaware could break off in months, or even weeks — an event that could signal the impending collapse of another of the southernmost continent’s ice shelves and an ominous sign of the impacts of a warming planet.
While that wouldn’t contribute to sea level rise around the world, ice shelves act as breaks for the flow of land ice, which lies behind them. Without ice shelves in their paths, glaciers slide more easily into the oceans, which would push up global sea levels.
The crack in the Larsen C shelf, already more than 100 miles long and slicing through 820 feet of ice, grew another six miles in just three weeks last month. Only 12 miles of ice connects the portion that’s at risk of breaking off from the rest of the shelf….