NSIDC: Arctic and Antarctic Sea Ice News for November 2016 -- lowest extent on record for November by large margin

Average Arctic sea ice extent for November set a record low, reflecting unusually high air temperatures, winds from the south, and a warm ocean. Since October, Arctic ice extent has been more than two standard deviations lower than the long-term average. Antarctic sea ice extent quickly declined in November, also setting a record low for the month and tracking more than two standard deviations below average during the entire month. For the globe as a whole, sea ice cover was exceptionally low.

Overview of conditions

Figure 1. Arctic sea ice extent for November 2016 was 9.08 million square kilometers (3.51 million square miles). The magenta line shows the 1981 to 2010 median extent for the month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. Credit: National Snow and Ice Data Center
High-resolution image

In November 2016, Arctic sea ice extent averaged 9.08 million square kilometers (3.51 million square miles), the lowest November in the satellite record. This is 800,000 square kilometers (309,000 square miles) below November 2006, the previous lowest November, and 1.95 million square kilometers (753,000 square miles) below the 1981 to 2010 long-term average for November. For the month, ice extent was 3.2 standard deviations below the long-term average, a larger departure than observed in September 2012 when the Arctic summer minimum extent hit a record low.

At this time of year, air temperatures near the surface of the Arctic Ocean are generally well below freezing, but this year has seen exceptional warmth. The overall rate of ice growth this November was 88,000 square kilometers (34,000 square miles) per day, a bit faster than the long-term average of 69,600 square kilometers (26,900 square miles) per day. However, for a brief period in the middle the month, total extent actually decreased by 50,000 square kilometers, or 19,300 square miles—an almost unprecedented occurrence for November over the period of satellite observations. A less pronounced and brief retreat of 14,000 square kilometers (5,400 square miles) occurred in 2013.

Ice growth during November as a whole occurred primarily within the Beaufort, Chukchi and East Siberian Seas, as well as within Baffin Bay. Ice extent slightly retreated in the Barents Sea for the month. Compared to the previous record low for the month set in 2006, sea ice was less extensive in the Kara, Barents, East Greenland, and Chukchi Seas, and more extensive in Baffin Bay this year.

Conditions in context

Figure 2a. The graph above shows daily Arctic sea ice extent as of December 5, 2016, along with daily ice extent data for four previous years. 2016 is shown in blue, 2015 in green, 2014 in orange, 2013 in brown, and 2012 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data. 
Credit: National Snow and Ice Data Center. High-resolution image

Figure 2b. This plot shows air temperature difference from average in the Arctic for November 2016. Air temperatures at the 925 hPa (approximately 2,500 feet) level in the atmosphere were above the 1981 to 2010 average over the entire Arctic Ocean and, locally up to 10 C (18 F) above average near the North Pole. This is in sharp contrast to northern Eurasia, where temperatures were up to 4-8 C (7-14 F) below average. Credit: NSIDC courtesy NOAA/ESRL Physical Sciences Division. High-resolution image

Continuing the warm Arctic pattern seen in October, November air temperatures were far above average over the Arctic Ocean and Canada. Air temperatures at the 925 hPa level (about 2,500 feet above sea level) were above the 1981 to 2010 average over the entire Arctic Ocean and, locally up to 10 degrees Celsius (18 degrees Fahrenheit) above average near the North Pole. This is in sharp contrast to northern Eurasia, where temperatures were as much as 4 to 8 degrees Celsius (7 to 14 degrees Fahrenheit) below average (Figure 2b). Record snow events were reported in Sweden and across Siberia early in the month.

In autumn and winter, the typical cyclone path is from Iceland, across the Norwegian Sea and into the Barents Sea. This November, an unusual jet stream pattern set up, and storms instead tended to enter the Arctic Ocean through Fram Strait (between Svalbard and Greenland). This set up a pattern of southerly wind in Fram Strait, the Eurasian Arctic and the Barents Sea and accounts for some of the unusual warmth over the Arctic Ocean. The wind pattern also helped push the ice northwards and helps to explain why sea ice in the Barents Sea retreated during November.

Sea surface temperatures in the Barents and Kara Seas remained unusually high, which also helped prevent ice formation. These high sea surface temperatures are a result of warm Atlantic water circulating onto the Arctic continental shelf seas.

November 2016 compared to previous years

Figure 3. Monthly November ice extent for 1979 to 2016 shows a decline of 5.0% per decade. Credit: National Snow and Ice Data Center. High-resolution image

Through 2016, the linear rate of decline for November is 55,400 square kilometers (21,400 square miles) per year, or 5.0% per decade.

Warm Arctic delays ice formation in Svalbard’s fjords

Figure 4a. This plot shows ocean temperature differences from average by depth (y-axis, in decibars; a decibar is approximately one meter) along a transect (x-axis, in kilometers) from the outer continental shelf to the inner parts of Isfjorden, the largest fjord in the Svalbard archipelago, for mid November 2016. (Areas in black show the undersea topography.) Atlantic Water is as warm as 5 C (41 F) and the surface layer still about 2 C (36 F). The surface layer would normally have cooled to the salinity adjusted freezing point at (-1.8 C, 29 F) at this time of year, enabling sea ice formation. Credit: University Centre in Svalbard. High-resolution image

Figure 4b. The West Spitsbergen Current consists of three branches (red arrows) that transport warm and salty Atlantic Water northward: the Return Atlantic Current (westernmost branch), the Yermak Branch and the Svalbard Branch. The Spitsbergen Trough Current (purple) transports Atlantic Water from the Svalbard Branch into the troughs indenting the shelf along Svalbard. Since 2006, changes in atmospheric circulation have resulted in more warm Atlantic Water reaching these fjords. The blue and red circles on the figure indicate locations where hydrographic data were collected. Credit: University Centre in Svalbard (UNIS). High-resolution image

Figure 4c. An inky-black polar night—but no cooling. The moon is the only source of light in the Arctic now, and here shines over open water in Isfjorden, the largest fjord in the Svalbard archipelago, in mid-November 2016. Credit: Lars H. Smedsrud. High-resolution image

In the Svalbard archipelago, sea ice usually begins to form in the inner parts of the fjords in early November. This November, however, no sea ice was observed. Throughout autumn, the wind pattern transported warm and moist air to Svalbard, leading to exceptionally high air temperatures and precipitation, which fell as rain.

Atmospheric and oceanic conditions in the fjord system were assessed by students from the University Centre in Svalbard. They noted an unusually warm ocean surface layer about 4 degrees Celsius (7 degrees Fahrenheit) above the salinity-adjusted freezing point (Figure 4a). Coinciding with exceptionally high air temperatures over Svalbard during autumn, the water has hardly cooled at all, and it is possible that no sea ice will form this winter.

The above-average ocean temperatures arose in part from changes in ocean currents that bring warm and salty Atlantic Water into the fjords. As the warm Gulf Stream moves east, it becomes the branching North Atlantic Drift. One small branch is named the West Spitsbergen Current (Figure 4b). This current flows along the continental shelf on the west coast of Svalbard and is one mechanism for transporting heat towards the fjords. Since 2006, changes in atmospheric circulation have resulted in more Atlantic water reaching these fjords, reducing sea ice production in some and stopping ice formation entirely in others.

Antarctic sea ice continues to track well below average

Figure 5a. Monthly November Antarctic sea ice extent for 1979 to 2016 shows an increase of 0.36% per decade. Credit: National Snow and Ice Data Center. High-resolution image

Figure 5b. This plot shows air temperature difference from average in the Antarctic for October 27 to November 17, 2016. Air temperatures at the 925 hPa level (approximately 2,500 feet) during the period of rapid sea ice decline in Antarctica (October 27 through November 17) were 2-4 C (4-7 F) above average near the sea ice edge. Credit: NSIDC courtesy NOAA/ESRL Physical Sciences Division. High-resolution image

Figure 5c. This map of sea ice concentration difference from average for November 2016 shows very low ice extent in three areas of the ice edge (near the Antarctic Peninsula, near the western Ross Sea and Wilkes Land, and near Enderby Land) as well as extensive areas of lower-than-average concentration within the interior ice pack in the Weddell Sea, Amundsen Sea, and near the Amery Ice Shelf. Sea Ice Index data. Credit: National Snow and Ice Data Center. High-resolution image

This year, Antarctic sea ice reached its annual maximum extent on August 31, much earlier than average, and has since been declining at a fairly rapid pace, tracking more than two standard deviations below the 1981-2010 average. This led to a new record low for the month of November over the period of satellite observations (Figure 5a). Average extent in November was 14.54 million square kilometers (5.61 million square miles). This was 1.0 million square kilometers (386,000 square miles) below the previous record low of 15.54 million square kilometers (6.00 million square miles) set in 1986 and 1.81 million square kilometers (699,000 square miles) below the 1981 to 2010 average.

For the month, Antarctic ice extent was 5.7 standard deviations below the long-term average. This departure from average was more than twice as large as the previous record departure from average, set in November 1986.

Ice extent is lower than average on both sides of the continent, particularly within the Indian Ocean and the western Ross Sea, but also to a lesser extent in the Weddell Sea and west of the Antarctic Peninsula in the eastern Bellingshausen Sea. Moreover, several very large polynyas (areas of open water within the pack) have opened in the eastern Weddell and along the Amundsen Sea and Ross Sea coast.

Air temperatures at the 925 mbar level were 2 -4 C (4-7 F) above average near the sea ice edge during late October and early November, corresponding to the period of rapid sea ice decline (Figure 5b).

The entire austral autumn and winter (since March 2016) was characterized by generally strong west to east winds blowing around the continent. This was associated with a positive phase of the Southern Annular Mode, or SAM. This pattern tends to push the ice eastward, but the Coriolis force acting in the ice adds a component of northward drift. During austral spring (September, October and November), the SAM index switched from strongly positive (+4 in mid-September, a record) to negative (-2.8 in mid-November). When the westerly wind pattern broke down in November, winds in several areas of Antarctica started to blow from the north. Over a broad area near Wilkes Land, the ice edge was pushed toward the continent. Areas with southward winds were also located between Dronning Maud Land and Enderby Land, and near the Antarctic Peninsula. This created three regions where ice extent quickly became much less extensive than usual (Figure 5c), reflected in the rapid decline in extent for the Antarctic as a whole. Interspersed with the areas of compressed sea ice and winds from the north, areas of south winds produced large open water areas near the coast, creating the polynyas.

Arctic sea ice loss linked to rising anthropogenic CO2 emissions

Figure 6. This plot shows the relationship between September sea ice extent (1953-2015) and cumulative CO2 emissions since 1850. Grey diamonds represent the individual satellite data values; circles represent pre-satellite era values; the solid red line shows the 30-year running average. The dotted red line indicates the linear relationship of 3 square meters per metric ton of CO2. Credit: J. Stroeve, National Snow and Ice Data Center High-resolution image

A new study published in the journal Science links Arctic sea ice loss to cumulative CO2 emissions in the atmosphere through a simple linear relationship (Figure 6). Researchers conducting the study, including NSIDC scientist Julienne Stroeve, examined this linear relationship based on observations from the satellite and pre-satellite era since 1953, and in climate models. The observed relationship is equivalent to a loss of 3 square meters (9.9 square feet) for every metric ton of CO2 added to the atmosphere, compared the average from all the climate models of 1.75 square meters (5.8 square feet). This smaller value, or lower sensitivity, from the models is consistent with findings that the models tend to be generally conservative relative to observations in regard to how fast the Arctic has been losing its summer ice cover. The observed rate of ice loss per metric ton of CO2 allows individuals to more easily grasp their contribution to Arctic sea ice loss.

Global sea ice far below average

Figure 7. This time series of daily global sea ice extent (Arctic plus Antarctic, month and first day of month on the x-axis) shows global extent tracking below the 1981-2010 average. Sea Ice Index data. Credit:W. Meier, NASA Cryospheric Sciences, GSFC. High-resolution image

As a result of both Arctic and Antarctic sea ice currently tracking at record low levels, global ice extent near November’s end stood at 7.3 standard deviations below average (Figure 7). However, the processes governing the evolution of sea ice in both hemispheres is a result of different atmospheric and oceanic processes and geographies and it unlikely that record low conditions in the two hemispheres are connected. Also, it is not especially instructive to assess a global sea ice extent because the seasons are opposite in the two hemispheres. In November the Arctic is in its ice growth season while Antarctic is losing ice. Antarctic sea ice as a whole has slightly increased over the past four decades (but with the last two austral winters having average and below average extent, respectively). The slight overall increase in Antarctic ice over the satellite record can be broadly linked to wind patterns that have helped to expand the ice cover towards the north (towards the equator).

NASA Operation IceBridge completes its 2016 Antarctic campaign

Figure 8. This photograph from Operation IceBridge shows broken floes of sea ice floating in the Weddell Sea. A large area of open water can be seen on the horizon. Credit: J. Beitler/National Snow and Ice Data Center. High-resolution image

In October, four NSIDC personnel accompanied the NASA Operation IceBridge campaign on its airborne surveys over Antarctica. The campaign completed a total of 24 flights over the continent in October and November, covering sea ice, land ice, ice shelves, and glaciers as Antarctica headed into its austral summer. Missions surveyed sea ice in the Weddell and Bellinghausen Seas with instruments that measure both sea ice extent and thickness. These measurements add to a time series of data that measures changes in sea ice and helps researchers assess the future trajectory of the ice pack and its impact on the climate. Visual observations from the flights confirmed that areas in the Bellingshausen Sea that are typically covered in sea ice were open water this year.

One of this year’s missions flew over a massive rift in the Antarctic Peninsula’s Larsen C Ice Shelf. Ice shelves are the floating parts of ice streams and glaciers, and they buttress the grounded ice behind them; when ice shelves collapse, the ice behind accelerates toward the ocean, where it then adds to sea level rise. Larsen C neighbors a smaller ice shelf that disintegrated in 2002 after developing a rift similar to the one now growing in Larsen C.

The IceBridge scientists measured the Larsen C fracture to be about 70 miles long, more than 300 feet wide and about a third of a mile deep. The crack completely cuts through the ice shelf but it does not go all the way across it. Once it does, it will produce an iceberg roughly the size of the state of Delaware.

The mission of Operation IceBridge is to collect data on changing polar land and sea ice and maintain continuity of measurements between NASA’s Ice, Cloud and Land Elevation Satellite (ICESat) missions. The original ICESat mission ended in 2009, and its successor, ICESat-2, is scheduled for launch in 2018. Operation IceBridge, which began in 2009, is currently funded until 2019. The planned overlap with ICESat-2 will help scientists validate the satellite’s measurements.

Further reading

Nilsen, F., Skogseth, R., Vaardal-Lunde, J., and Inall, M. 2016. A simple shelf circulation model: Intrusion of Atlantic Water on the West Spitsbergen Shelf. J. Physical Oceanography, 46, 1209-1230. doi:10.1175/JPO-D-15-0058.1

Notz, D. and J. Stroeve. 2016. Observed Arctic sea-ice loss directly follows anthropogenic CO2 emission. Science, 11 Nov 2016: Vol. 354, Issue 6313, pp. 747-750. doi:10.1126/science.aag2345.

Parkinson, C. 2014. Global sea ice coverage from satellite data: Annual cycle and 35-year trends. Journal of Climate, December 2014. doi:10.1175/JCLI-D-14-00605.1.

References

Fetterer, F., K. Knowles, W. Meier, and M. Savoie. 2016, updated daily. Sea Ice Index, Version 2. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi:10.7265/N5736NV7.

http://nsidc.org/arcticseaicenews/

'Incredible' rate of polar ice loss alarms scientists: loss from Greenland doubles in just 5 years

A European satellite has shown ice sheets shrinking at 120 cubic miles a year in Antarctica and Greenland

by Robin McKie, The Observer, August 23, 2014

An artist’s impression of CryoSat-2, the European satellite which has revealed dramatic ice loss. Photograph: ESA

The planet's two largest ice sheets – in Greenland and Antarctica – are now being depleted at an astonishing rate of 120 cubic miles each year. That is the discovery made by scientists using data from CryoSat-2, the European probe that has been measuring the thickness of Earth's ice sheets and glaciers since it was launched by the European Space Agency in 2010.

Even more alarming, the rate of loss of ice from the two regions has more than doubled since 2009, revealing the dramatic impact that climate change is beginning to have on our world.

The researchers, based at Germany's Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research – used 200 million data points across Antarctica and 14.3 million across Greenland, all collected by CryoSat, to study how the ice sheets there had changed over the past three years. The satellite carries a high-precision altimeter, which sends out short radar pulses that bounce off the ice surface and then back to the satellite. By measuring the time this takes, the height of the ice beneath the spacecraft can be calculated.

It was found from the average drops in elevation that were detected by CryoSat that Greenland alone is losing about 90 cubic miles a year, while in Antarctica the annual volume loss is about 30 cubic miles. These rates of loss – described as "incredible" by one researcher – are the highest observed since altimetry satellite records began about 20 years ago, and they mean that the ice sheets' annual contribution to sea-level rise has doubled since 2009, say the researchers whose work was published in the journal Cryosphere last week.

"We have found that, since 2009, the volume loss in Greenland has increased by a factor of about two, and the West Antarctic ice sheet by a factor of three," said glaciologist Angelika Humbert, one of the study's authors. "Both the West Antarctic ice sheet and the Antarctic peninsula, in the far west, are rapidly losing volume. By contrast, East Antarctica is gaining volume, though at a moderate rate that doesn't compensate for the losses on the other side of the continent."

The researchers say they detected the biggest elevation changes caused by ice loss at the Jakobshavn glacier in Greenland, which was recently found to be shifting ice into the oceans faster than any other ice-sheet glacier, and at Pine Island glacier, which like other glaciers in West Antarctica, has been thinning rapidly in recent years.

The discovery of these losses of ice is particularly striking and represents yet another blow to claims by some climate-change deniers, who argue that the rapid loss of ice in the Arctic currently being observed is being matched by a corresponding increase in Antarctica. CryoSat's measurements show that Antarctica – although considerably colder than the Arctic because of its much higher average elevation – is not gaining ice at all. Indeed, it is – overall – losing considerable volumes, and in the case of West Antarctica is doing so at an alarming rate.

This point was stressed by Mark Drinkwater, the European Space Agency's CryoSat mission scientist. "These results offer a critical new perspective on the recent impact of climate change on large ice sheets. This is particularly evident in parts of the Antarctic peninsula, where some of the more remarkable features add testimony on the impact of sustained peninsula warming at rates several times the global average."

http://www.theguardian.com/environment/2014/aug/24/incredible-polar-ice-loss-cryosat-antarctica-greenland

Peter Sinclair: Point of No Return, Deglaciation of West Antarctica, Meltwater Pulse 2B

by Peter Sinclair, This Is Not Cool, June 2, 2014

Today’s news will be dominated by discussion of new carbon regulations proposed by the Obama administration.  My contribution is to summarize the most recent evidence for why those regs are needed today, if not 25 years ago.

Bud Ward at Yale Climate Connections:

It’s not often that a scientific research paper generates the kind of media attention and scientific community buzz that resulted from a recent study on the apparent inevitability of substantial Antarctic glacial melting.

The early May research headed by lead author Eric Rignot of NASA called attention to melting now under way in Antarctica that CBS News anchor Scott Pelley reported “cannot be stopped.”

“Scientists say the situation is almost certainly unstoppable,” NBC News Anchor Brian Mitchell reported.

Rignot cautioned that the research indicates “we’ve passed the point of no return … It’s just a matter of time before these glaciers disappear to the sea.” While he indicated that the full melt, at the current pace, might not occur for two centuries, he pointed too to evidence suggesting the likelihood of an accelerating pace.

“There’s probably nothing that can be done to stop this,” Rignot said.

“This is really happening,” lead NASA lead polar ice researcher Tom Wagner said. “This weak underbelly of Antarctica is in fact starting to float out into the sea, and there’s not a lot to hold it back.”

A “This is Not Cool” video on the report by independent videographer Peter Sinclair is the first to be posted under the new Yale Climate Connections name, formerly The Yale Forum on Climate Change & The Media. The official transition to that newly named site is to get underway over the next few weeks, initially with a largely cosmetic rebranding, then to be followed by a substantial overhaul and a more multi-media emphasis aimed at better reaching the general public.

Note: link to the Guardian piece referenced in the video is here. Errata – I neglected to thank the European Space Agency for important video animations. Deepest apologies.

UPDATE: Per Stefan Rahmstorf, newly published study adds complexity.

eScience News:

“Conventional thinking based on past research is that the Antarctic Ice Sheet has been relatively stable since the last ice age, that it began to melt relatively late during the deglaciation process, and that its decline was slow and steady until it reached its present size,” said lead author Michael Weber, a scientist from the University of Cologne in Germany.

“The sediment record suggests a different pattern — one that is more episodic and suggests that parts of the ice sheet repeatedly became unstable during the last deglaciation,” Weber added.

The research also provides the first solid evidence that the Antarctic Ice Sheet contributed to what is known as meltwater pulse 1A, a period of very rapid sea level rise that began some 14,500 years ago, according to Peter Clark, an Oregon State University paleoclimatologist and co-author on the study.

The largest of the 8 episodic pulses outlined in the new Nature study coincides with meltwater pulse 1A.

“During that time, the sea level on a global basis rose about 50 feet in just 350 years — or about 20 times faster than sea level rise over the last century,” noted Clark, a professor in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences. “We don’t yet know what triggered these eight episodes or pulses, but it appears that once the melting of the ice sheet began it was amplified by physical processes.”

The researchers suspect that a feedback mechanism may have accelerated the melting, possibly by changing ocean circulation that brought warmer water to the Antarctic subsurface, according to co-author Axel Timmermann, a climate researcher at the University of Hawaii at Manoa.

“This positive feedback is a perfect recipe for rapid sea level rise,” Timmermann said.

Some 9,000 years ago, the episodic pulses of melting stopped, the researchers say.

“Just as we are unsure of what triggered these eight pulses,” Clark said, “we don’t know why they stopped. Perhaps the sheet ran out of ice that was vulnerable to the physical changes that were taking place. However, our new results suggest that the Antarctic Ice Sheet is more unstable than previously considered.”

http://climatecrocks.com/2014/06/02/new-video-meltwater-pulse-2b/http://climatecrocks.com/2014/06/02/new-video-meltwater-pulse-2b/

Dr. Mauri Pelto interviewed by Peter Sinclair on Antarctic melt, Part II

interview by Peter Sinclair, Weekend Wonk, May 18, 2014

Link:  http://climatecrocks.com/2014/05/18/the-weekend-wonk-dr-mauri-pelto-on-antarctic-melt-part-2/

Dr. Mauri Pelto discusses the Pine Island Glacier and the two recent papers on the Western Antarctic Ice Sheet, Part I

interview by Peter Sinclair, Climate Crocks, May 17, 2014


Link:  http://climatecrocks.com/2014/05/17/the-weekend-wonk-dr-mauri-pelto-on-antarctic-melt-part-1/

Joe Romm: New Studies Suggest Many Coastal Cities Eventually To Be Abandoned With Antarctic Ice Collapse

by Joe Romm, Climate Progress, May 13, 2014

West Antarctica’s Thwaites glacier, one of a cluster that appear to have started irreversible collapse, threatening devastating sea level rise. Via NASA.

New studies in Science and Geophysical Research Letters (GRL) find that glaciers in the Amundsen Sea region of the great Antarctic ice sheet have begun the process of irreversible collapse. That by itself would raise sea levels 4 feet in the coming centuries.

But more importantly these glaciers act “as a linchpin on the rest of the [West Antarctic] ice sheet, which contains enough ice to cause” a total of 12 to 15 feet of global sea level rise, as the University of Washington news release for the Science study explains.

What most of the media has failed to emphasize is that (1) this is not a worst-case scenario and (2) failure to curb carbon pollution ASAP will result in vastly higher levels of sea level rise that devastate the world’s coastlines.

NASA’s Eric Rignot, lead author of the GRL study, explains the basic scientific findings in this video:

The New York Times story on the studies warns:

[Climatologist Richard Alley] added that while a large rise of the sea may now be inevitable from West Antarctica, continued release of greenhouse gases will almost certainly make the situation worse. The heat-trapping gases could destabilize other parts of Antarctica as well as the Greenland ice sheet, potentially causing enough sea-level rise that many of the world’s coastal cities would eventually have to be abandoned.

“If we have indeed lit the fuse on West Antarctica, it’s very hard to imagine putting the fuse out,” Dr. Alley said. “But there’s a bunch more fuses, and there’s a bunch more matches, and we have a decision now: Do we light those?”

But for some reason the New York Times buries these bombshells at the very end of a long piece. Even more inexplicably, the Times changed its online headline for the story from

to an indefensibly lamer one:

That new headline cuts out the heart of the news. It could have been used in stories about literally dozens of studies in the past quarter century. Heck, the New York Times headline in 1981 (!) for a NASA study led by James Hansen was … wait for it … “STUDY FINDS WARMING TREND THAT COULD RAISE SEA LEVELS.”

Apparently somebody associated with the Times thought the headline and lede were too strong, that “collapse” is somehow an inappropriate word that needed to be excised.

But it wasn’t. The headline of the news release from NASA and UC-Irvine (for the GRL study) was:

NASA-UCI Study Indicates Loss of West Antarctic Glaciers Appears Unstoppable

The Science study is titled, “Marine Ice Sheet Collapse Potentially Under Way for the Thwaites Glacier Basin, West Antarctica.” The headline from the news release is:

West Antarctic Ice Sheet collapse is under way

So the original NY Times story was accurate: the revised version, less so.

I asked Rignot for his thoughts on whether his study (along with the other) means we should revise the upper estimate for sea level rise this century (and beyond) if we stay on our current emissions path, which will take us to 4 °C (7 °F) warming or more by 2100. He replied:

I think that the minimum will be the upper end of the IPCC projections (90 cm) by 2100 and the maximum is hard to figure out but will likely exceed 1.2–1.4 meters.

The systems we are looking at do not respond to climate forcing in a smooth way, they start slow and then they proceed faster and faster. I am not convinced the numerical models are there yet, they are still conservative and do not include all the feedbacks, they are getting better than IPCC-class models but still trailing reality quite a bit.

After 2100, it will be several meters from the ice sheets, there is no red button to stop that. I surely hope that by then humanity will have reacted and slowed down the warming. I do not think we want to experience how fast Antarctica could fall apart if we push it hard … as we do now.

So the upper end of sea level rise will likely exceed 48 to 56 inches! That would not leave “southeastern Florida having many people at the end of this century,” to quote Hal Wanless, chair of the geological sciences department at University of Miami, from a 2013 interview.

The fact that these models do not include all the feedbacks and are conservative is a key point missed by much of the media. The Science article’s abstract concludes, “Less certain is the time scale, with the onset of rapid (>1 mm per year of sea-level rise) collapse in the different simulations within the range of 200 to 900 years.”

The article itself points out:

An important feature of our numerical simulations is that they reveal a strong sensitivity to mechanical and/or rheological weakening of the margins, which can accelerate the rate of collapse by decades to centuries. Thus, future models will require careful treatment of shear margins to accurately project sea-level rise. Our simulations also assume that there is no retreat of the ice-shelf front. Full or partial ice-shelf collapse should produce more rapid retreat than we have simulated. In addition, we have not modeled ocean-driven melt that extends immediately upstream of the grounding line, which could also accelerate retreat.

Of course we know from a 2012 Nature study that Antarctica is melting from below, which “may already have triggered a period of unstable glacier retreat.”

The new Science study (Joughin et al.) also notes:

Our simulations are not coupled to a global climate model to provide forcing nor do they include an ice-shelf cavity-circulation model to derive melt rates…. As such, our simulations do not constitute a projection of future sea level in response to projected climate forcing.

Again, things could go faster and be much worse than this study suggests — as shown by Nature’s bombshell study on observations pointing to 10 °F warming by 2100.

Also, the West Antarctic Ice Sheet (WAIS) is only one contributor to sea level rise. We know Greenland’s ice melt is up nearly 5-fold since the mid-1990s, as we reported in late 2012. And parts of the East Antarctic Ice Sheet are not stable either — and have points of no return, as we reported earlier this month.

That was a point Dr. Alley made to me:

Joughin et al. didn’t run a worst-case scenario, as they state. So, it is possible that a worst-case version would shift the time of rapid retreat forward into this century. I don’t think we know yet, and I think that there is plenty of science to do, incorporating the new Rignot et al. data, and other measurements and ideas that many groups including Penn State have been working on.

And, maybe most important, if we have committed to 3 m or so of globally averaged sea-level rise from West Antarctica, even if delayed by many centuries, the costs are sobering, but are not as high as the costs of also committing to loss of Greenland’s ice and parts of East Antarctica’s ice as well. And, while some additional shrinkage of Greenland probably is already committed, major loss in Greenland and East Antarctica is not guaranteed yet. Too much warming is expected to cause major loss, with Greenland not too many degrees away and East Antarctica more uncertain. But, even with such a sobering possibility on the table, the costs are likely to rise faster than the temperature, so that each degree of warming costs more than the previous degree, and adding Greenland’s ice or parts of East Antarctica’s ice to the marine parts of West Antarctica would raise the costs a lot more.

In short, the fact that we may be stuck with 10 feet of sea level rise from WAIS over the next 200 to 900 years or so doesn’t mean we should stay on a CO2 emissions path that would (1) make it far more likely WAIS collapses sooner rather than later and (2) guarantees accelerated melting and/or collapse of large parts of Greenland and EAIS, too, leading to many tens of feet of sea level rise, and ultimately loss of virtually all land-based ice — raising seas over 200 feet.

The fact that such an unimaginable catastrophe would probably take many, many centuries to occur does not make it any less immoral for us — if we are the ones who make that outcome unstoppable.

I’ll end with the comments sent to me by sea-level-rise expert Stefan Rahmstorf, Co-Chair of Earth Systems Analysis, Potsdam Institute for Climate Impact Research:

What climate scientists have feared for decades is now beginning to come true: We are pushing the climate system across dangerous tipping points. Beyond such points, things like ice sheet collapse become self-sustaining and unstoppable, committing our children and children’s children to massive problems. The new studies strongly suggest the first of these tipping points has already been crossed. More tipping points lie ahead of us. I think we should try hard to avoid crossing them.

http://thinkprogress.org/climate/2014/05/13/3437033/coastal-cities-abandoned/