WaPo: The melting of Antarctica was already really bad. It just got worse

by Chris Mooney, The Washington Post, March 16, 2015

A satellite view of Antarctica is seen in this undated NASA handout photo obtained by Reuters on February 6, 2012. (NASA handout via Reuters)

This story has been updated.

A hundred years from now, humans may remember 2014 as the year that we first learned that we may have irreversibly destabilized the great ice sheet of West Antarctica, and thus set in motion more than 10 feet of sea level rise.

Meanwhile, 2015 could be the year of the double whammy — when we learned the same about one gigantic glacier of East Antarctica, which could set in motion roughly the same amount all over again. Northern Hemisphere residents and Americans in particular should take note — when the bottom of the world loses vast amounts of ice, those of us living closer to its top get more sea level rise than the rest of the planet, thanks to the law of gravity.

The findings about East Antarctica emerge from a new paper just out in Nature Geoscience by an international team of scientists representing the United States, Britain, France and Australia. They flew a number of research flights over the Totten Glacier of East Antarctica — the fastest-thinning sector of the world’s largest ice sheet — and took a variety of measurements to try to figure out the reasons behind its retreat. And the news wasn’t good: It appears that Totten, too, is losing ice because warm ocean water is getting underneath it.

“The idea of warm ocean water eroding the ice in West Antarctica, what we’re finding is that may well be applicable in East Antarctica as well,” says Martin Siegert, a co-author of the study and who is based at the Grantham Institute at Imperial College London.

[Research casts alarming light on the decline of West Antarctic glaciers]

The floating ice shelf of the Totten Glacier covers an area of 90 miles by 22 miles. It it is losing an amount of ice “equivalent to 100 times the volume of Sydney Harbour every year,” notes the Australian Antarctic Division.

That’s alarming, because the glacier holds back a much more vast catchment of ice that, were its vulnerable parts to flow into the ocean, could produce a sea level rise of more than 11 feet — which is comparable to the impact from a loss of the West Antarctica ice sheet. And that’s “a conservative lower limit,” says lead study author Jamin Greenbaum, a PhD candidate at the University of Texas at Austin.

In its alignment with the land and the sea, the Totten Glacier is similar to the West Antarctic glaciers, which also feature ice shelves that slope out from the vast sheet of ice on land and extend into the water. These ice shelves are a key source of instability, because if ocean waters beneath them warm, they can lose ice rapidly, allowing the ice sheet behind them to flow more quickly into the sea.

The researchers used three separate types of measurements taken during their flights — gravitational measurements, radar and laser altimetry — to get a glimpse of what might be happening beneath the massive glacier, whose ice shelves are more than 1,600 feet thick in places. Using radar, they could measure the ice’s thickness. Meanwhile, by measuring the pull of the Earth’s gravity on the airplane in different places, the scientists were able to determine just how far below that ice the seafloor was.

The result was the discovery of two undersea troughs or valleys beneath the ice shelf — regions where the seafloor slopes downward, allowing a greater depth of water beneath the floating ice. These cavities or subsea valleys, the researchers suggest, may explain the glacier’s retreat — they could allow warmer deep waters to get underneath the ice shelf, accelerating its melting.

Aerial photo of Totten Glacier’s ice shelf edge taken during one of the team’s geophysical survey flights. (Jamin Greenbaum)

In this particular area of Antarctica, Greenbaum says, a warmer layer of ocean water offshore is actually deeper than the colder layers above it, because of the saltwater content of the warm water (which increases its density). And the canyons may allow that warm water access to the glacier base. “What we found here is that there are seafloor valleys deeper than the depth of the maximum temperature measured near the glacier,” Greenbaum says.

One of these canyons is three miles wide, in a region that was previously believed to simply hold ice lying atop solid earth. On the contrary, the new study suggests the ice is instead afloat.

The availability of warm water, and the observed melting, notes the study, “support the idea that the behaviour of Totten Glacier is an East Antarctic analogue to ocean-driven retreat underway in the West Antarctic Ice Sheet (WAIS). The global sea level potential of 3.5 m flowing through Totten Glacier alone is of similar magnitude to the entire probable contribution of the WAIS.”

For Richard Alley, a glaciologist at Penn State University, the new research hints at a possible solution to a question that scientists have long had about the planet’s past — and in particular the Pliocene epoch, beginning 5.3 million years ago, when sea levels were dramatically higher, by as much as 40 meters.

“The sea-level indicators from the Pliocene have suggested that an important amount of ice came out of East Antarctica into the ocean,” says Alley. “Sedimentary records offshore pointed in the same way, and recent modeling…shows the strong potential for this to have happened.  This new paper adds to the evidence — the pieces are fitting together.”

One limitation of the study is that the scientists were not able to directly measure the temperature of ocean water that is reaching the glacier itself. While this could be done with robotic underwater vehicles or other methods, that wasn’t part of the study at this time. Thus, the conclusions are more focused on inferring the vulnerability of the glacier based on a number of different pieces of evidence — topped off by the fact that the glacier is, indeed, retreating.

“What we need now is a confirmation of the findings of the paper from oceanographic data, because it  is one thing to find potential pathways for warm water to intrude the cavity, it is another to show that this is actually happening,” observes Eric Rignot, an Antarctica expert at the University of California, Irvine. “This paper comes short of the latter, but other research efforts are underway to get critical oceanographic information near Totten.”

[These subsea drones are figuring out just how badly we are messing up the planet]

Maximum Antarctic sea ice 2014(0:42)

An animation of the Antarctic sea ice between March 21 and September 19, 2014, when the sea ice reached its maximum extent. The red extent line shows the average of the annual maximum extents from 1979 through 2014. (NASA)

For residents of the United States — and indeed, the entire Northern Hemisphere — the impact of major ice loss from Antarctica could be dire. If Antarctica loses volumes of ice that would translate into major contributions to sea level rise, that rise would not be distributed evenly around the globe. The reason is the force of gravity. Antarctica is so massive that it pulls the ocean toward it, but if it loses ice, that gravitational pull will relax, and the ocean will slosh back toward the Northern Hemisphere — which will experience additional sea level rise.

For the United States, the amount of sea level rise could be 25 percent or more than the global average.

[The U.S. has caused more global warming than any other country. Here's how the Earth will get its revenge.]

Much as with the ocean-abutting glaciers of West Antarctica, just because a retreat has been observed — and because the entirety of the region implies a sea level rise of 11 or more feet were all ice to end up in the ocean — does not mean that we’ll see anything near that much sea level rise in our lifetimes. These processes generally are expected to play out over hundreds of years or more. They would reshape the face of the Earth – but we may never see it.

The problem, then, is more the world we’re leaving to our children and grandchildren — because once such a gigantic geophysical process begins, it’s hard to see how it comes to a halt. “With warming oceans, it’s difficult to see how a process that starts now would be reversed, or reversible, in a warming world,” Siegert says.

Update: This article was updated to correct the size of the Totten Glacier. According to Greenbaum (but contrary to this press release), its floating portion (or ice shelf) is 90 miles by 22 miles in size. 

http://www.washingtonpost.com/news/energy-environment/wp/2015/03/16/the-melting-of-antarctica-was-already-really-bad-it-just-got-worse/

Millennial Scale Change From Lake El’gygytgyn, NE Russia: Did We Step Or Leap Out Of The Warm Pliocene Into The Pleistocene?

43rd International Arctic Workshop, Amherst, Mass., March 11-13, 2014

Julie Brigham-Grette¹, Martin Melles², Pavel Minyuk³, and the El'gygytgyn Science Team⁴

¹University of Massachusetts, Amherst
²University of Cologne
³NEISRI-RAS Magadan
⁴USA, Germany, Russia

The Pliocene-Pleistocene climate evolution of the Arctic must have modulated the glacial history of Greenland and the onset of Northern Hemisphere glaciation. What is known from the terrestrial stratigraphy of Arctic climate change comes from sites that are spatially and temporally fragmented. In 2009, International Continental Deep Drilling at Lake El’gygytgyn (67^o 30' N, 172^o 05' E) recovered lacustrine sediments dating back to 3.58 Ma that provide the first time-continuous Pliocene-Pleistocene Arctic paleoclimate record of alternating glacial-interglacial change. The warmest/wettest Pliocene interval of the lake record occurs from ~3.58-3.34 Ma and is dominated by exceptional tree pollen implying July temperatures nearly 7-8 ^oC warmer than today, with nearly ~3 times the annual precipitation. Atmospheric CO2 levels are estimated to have been 360-400 ppm implying exceptionally high climate sensitivity and polar amplification. In fact, pollen spectra and modern analog analysis show an unbroken persistence of summers much warmer and wetter than the last interglacial, MIS 5e until nearly 2.2 Ma. Extreme warmth in the Mid Pliocene Arctic occurs at the same time ANDRILL results suggest the West Antarctic Ice Sheet was non-existent.

Using physical, chemical, and biological proxies we find pronounced glacial episodes commenced ~2.6 Ma ago, but the full range of typical Pleistocene glacial/interglacial change was not established until ~1.8 Ma ago. Greenland must have also responded to numerous “super interglacials” during the Quaternary record, with maximum summer temperatures and annual precipitation, especially during MIS 9, 11 and 31, at Lake El’gygytgyn exceeding that documented for MIS 5e. The correspondence of many of these super-interglacials with retreat of the West Antarctic Ice Sheet (Naish et al. 2009) could coincide with intervals when the Greenland Ice was reduced in size. The climate record from Lake El’gygytgyn, especially the history of past interglacials, provides a fresh means of testing the evolving magnitude of polar amplification over time, and the sensitivity of the Greenland Ice Sheet to extreme warmth in the rest of the Arctic.

Brigham-Grette, J., Melles, M., Minyuk, P., Andreev, A., Tarasov, P., DeConto, R., Koenig, S., Nowaczyk, N., Wennrich, V., Rosén, P., Haltia-Hovi, E., Cook, T., Gebhardt, T., Meyer-Jacob, C., Snyder, J., Herzschuh, U.  Pliocene warmth, extreme polar amplification, and stepped Pleistocene cooling recorded in NE Russia. Submitted to Science, 21 November 2012; in revision March 2013.

Melles, M., Brigham-Grette, J., Minyuk, P., and others. 2012. 2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia. Science, 337, 315-320.

Naish, T. et al., 2009. Obliquity-paced Pliocene West Antarctic ice sheet oscillations. Nature, 458, 322-328.

See also Climate of the Past, special issue on Lake El’gygytgyn, 20+ manuscripts.

http://instaar.colorado.edu/meetings/AW2013/abstract_details.php?abstract_id=78

"Ice plug prevents irreversible discharge from East Antarctica," by M. Mengel & A. Levermann, Nature Climate Change (2014); doi: 10.1038/nclimate2226

Nature Climate Change, (4 May 2014); doi: 10.1038/nclimate2226

Ice plug prevents irreversible discharge from East Antarctica

M. Mengel and A. Levermann

Abstract

Changes in ice discharge from Antarctica constitute the largest uncertainty in future sea-level projections, mainly because of the unknown response of its marine basins¹. Most of West Antarctica’s marine ice sheet lies on an inland-sloping bed² and is thereby prone to a marine ice sheet instability^3,4,5. A similar topographic configuration is found in large parts of East Antarctica, which holds marine ice equivalent to 19 m of global sea-level rise⁶, that is, more than five times that of West Antarctica. Within East Antarctica, the Wilkes Basin holds the largest volume of marine ice that is fully connected by subglacial troughs. This ice body was significantly reduced during the Pliocene epoch⁷. Strong melting underneath adjacent ice shelves with similar bathymetry⁸ indicates the ice sheet’s sensitivity to climatic perturbations. The stability of the Wilkes marine ice sheet has not been the subject of any comprehensive assessment of future sea level. Using recently improved topographic data⁶ in combination with ice-dynamic simulations, we show here that the removal of a specific coastal ice volume equivalent to less than 80 mm of global sea-level rise at the margin of the Wilkes Basin destabilizes the regional ice flow and leads to a self-sustained discharge of the entire basin and a global sea-level rise of 3–4 m. Our results are robust with respect to variation in ice parameters, forcing details and model resolution as well as increased surface mass balance, indicating that East Antarctica may become a large contributor to future sea-level rise on timescales beyond a century.

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2226.html

Peter Sinclair: Making the Plio Scene – What the Past tells us about Sea Level

by Peter Sinclair, This Is Not Cool, December 5, 2013

The most sobering evidence of the planet's response to greenhouse gases comes from the fossil record. New evidence scientists are collecting suggests that ice sheets may be more vulnerable than previously believed, which has huge implications for sea level rise.

Link:  http://climatecrocks.com/2013/12/05/new-video-making-the-plio-scene-what-the-past-tells-us-about-sea-level/

David Spratt: Is climate change already dangerous? Part III. Consequences from current greenhouse gas levels

by David Spratt, Climate Code Red, September 22, 2013

Third in a series

Danger from implied temperature increase

The current level of atmospheric CO2 only is sufficient to increase the global temperature at equilibrium by +1.5 °C, based on the standard assumption of near-term climate sensitivity of 3 °C for doubled CO2.

If all current greenhouse gases are taken into account, then: 

The observed increase in the concentration of greenhouse gases (GHGs) since the pre-industrial era has most likely committed the world to a warming of 2.4 °C (within a range of +1.4 °C to +4.3 °C) above the pre-industrial surface temperatures (Ramanthan and Feng).

And the 2007 IPCC Synthesis report (Table 5.1 on emission scenarios) also shows that for levels of greenhouse gases that have already been achieved (CO2 in the range of 350–400 ppm, CO2e in the range 445–490 ppm) and peaking by 2015, the likely temperature rise is in the range of 2–2.4 °C. 

These scenarios include short-lived gases such as methane, which degrades out of the atmosphere in a decade, and also nitrous oxide, which has an atmospheric lifetime of around a century. On the other hand, the fact that temperatures are not already much higher than they are today is due principally to the large-scale emission of very short-lived (10 days) aerosols, such as soot and exhaust from burning fossil fuels, industrial pollution, and dust storms, which are providing temporary cooling. The effect is known popularly as “global dimming,” because the overall aerosol impact is to reduce, or dim, the sun’s radiation, thus masking some of the heating effect of greenhouse gases. The aerosol impact is not precisely known, but Ramanthan and Feng estimate it as high as ~1 °C. As the world moves to low-emission technologies, most of the aerosols and their temporary cooling will be lost. Recent research finds that quickly eliminating all greenhouse gas emissions (and necessarily the associated aerosols) would produce warming of between 0.25 and 0.5 °C over the decade immediately following (Matthews and Zickfield; Hansen, Sato et al.).

A practical consideration of “dangerous” can include the question as to whether there are tipping points or “concerns” activated for the elevated temperatures that we are generally considered to be already committed to: conservatively in the range say +1.5 to 2 °C and, more pragmatically, in the range of 2 to 2.4 °C if all current greenhouse gases are considered. A related question is whether the +1.5 °C goal advocated by the small island states and surveyed recently by Climate Action Network Europe and Climate Analytics would avoid “dangerous” climate change and significant tipping points.

This is a broad topic, but four recent important research findings on impacts for the current committed warming are arresting:

Greenland Ice Sheet tipping point

The tipping point for GIS has been revised down by Robinson, Calov et al. to +1.6 ºC (uncertainty range of +0.8 to +3.2 ºC) above pre-industrial, just as regional temperatures are increasing at three-to-four times faster than the global average, and the increased heat trapped in the Arctic due to the loss of reflective sea ice ensures an acceleration in the Greenland melt rate.  If the lower Greenland boundary in the uncertainty range turned out to be right, then with current warming of +0.8 ºC over pre-industrial we have already reached Greenland’s tipping point.  And, with temperature rises in the pipeline, the upward trajectory of annual greenhouse gas emissions, the projected future increases in fossil fuel use, and the continuing political impasse in international climate negotiations, we are very likely to hit the best estimate of +1.6 ºC within a decade or two at most.

Coral reefs

Frieler, Meinshausen et al. show that “preserving more than 10 per cent of coral reefs worldwide would require limiting warming to below +1.5 °C (atmosphere–ocean general circulation models (AOGCMs) range: 1.3–1.8 °C) relative to pre-industrial levels”.  Obviously at less than 10 per cent, the reefs would be remnant, and reef systems as we know them today would be a historical footnote.  Already, the data suggests that the global area of reef systems has already been reduced by half. A sober discussion of coral reef prospects can be found in Roger Bradbury’s “A World Without Coral Reefs” and Gary Pearce’s “Zombie reefs as a harbinger for catastrophic future.”  The opening of Bradbury’s article is to the point: 

It’s past time to tell the truth about the state of the world’s coral reefs, the nurseries of tropical coastal fish stocks.  They have become zombie ecosystems, neither dead nor truly alive in any functional sense, and on a trajectory to collapse within a human generation.  There will be remnants here and there, but the global coral reef ecosystem — with its storehouse of biodiversity and fisheries supporting millions of the world’s poor — will cease to be.

3c. Arctic carbon stores

As Climate Progress recently noted: “We’ve known for a while that ‘permafrost’ was a misnomer” because thawing permafrost feedback will turn the Arctic from a net carbon sink to a net source in the 2020s and defrosting permafrost will likely add up to 1 ºC to total global warming by 2100.   A 2012 UNEP report on policy implications of warming permafrost says the recent observations “indicate that large-scale thawing of permafrost may have already started.”  In February 2013, scientists using radiometric dating techniques on Russian cave formations to measure historic melting rates warned that a +1.5 ºC global rise in temperature compared to pre-industrial was enough to start a general permafrost melt.  Vaks, Gutareva et al. found that “global climates only slightly warmer than today are sufficient to thaw extensive regions of permafrost.” Vaks says that: “1.5 ºC appears to be something of a tipping point.”

Previously a study of East Siberian permafrost by Khvorostyanov, Ciais et al.  found that once mobilised, the process would be self-maintaining due to “deep respiration and methanogenesis” (formation of methane by microbes).  In other words, the microbial action that produces methane as the carbon stores melt would produce sufficient heat to maintain the process: “once active layer deepening in response to atmospheric warming is enough to trigger deep-soil respiration, and soil microorganisms are activated to produce enough heat, the mobilization of soil carbon can be very strong and self-sustainable.”

A sharp scientific debate has started on the stability of large methane clathrate stores just below the ocean floor on the shallow East Siberian Sea, following the publication in July 2013 of research by Whiteman, Hope and Wadhams which said that the release of a single giant “pulse” of methane from thawing Arctic permafrost beneath the East Siberian Sea could come with a $60 trillion global price tag. Wadhams says “the loss of sea ice leads to seabed warming, which leads to offshore permafrost melt, which leads to methane release, which leads to enhanced warming, which leads to even more rapid uncovering of seabed,” and this is not “a low probability event.”

Multiple targets reduce allowable warming

Steinacher, Joos et al. explore the interaction of targets in emissions reductions, focusing on the 2 ºC temperature goal. They find that when multiple climate targets are set (such as food production capacity, ocean acidity, atmospheric temperature), “allowable cumulative emissions are greatly reduced from those inferred from the temperature target alone.” In fact, “When we consider all targets jointly, CO2 emissions have to be cut twice as much as if we only want to meet the 2 ºC target.”

Lessons from climate history

Another fruitful line of inquiry on whether climate change is already “dangerous” is to look at the paleo-climate (climate history) record for circumstances analogous to present conditions to learn what planetary and climate conditions were like at that time.  With current CO2 levels at 400 ppm, a useful comparison is the Pliocene (3–5 million years ago).  The research body is large and growing in this area, but here are some examples:

Sea-levels

Rohling, Grant et al.  find that during the mid-Pliocene, when greenhouse gases were similar to today, sea levels were more than 20 metres higher than today “we estimate sea level for the Middle Pliocene epoch (3.0–3.5 Myr ago) – a period with near-modern CO2 levels – at 25 ±5 metres above present, which is validated by independent sea-level data.” Likewise Hansen, Sato et al. find that “during the middle-Pliocene… we find sea level fluctuations of 20–40 metres associated with global temperature variations between today’s temperature and +3 °C.”

Speed of sea-level rise

The speed of sea-level rise may far exceed the current, rather reticent estimates that are used for policy purposes.  Blancon, Eisenhauer et al. examined the paleo-climate record and showed a sea-level rises of 3 metres in 50 years due to the rapid melting of ice sheets 123,000 years ago in the Eemian, when the energy imbalance in the climate system was less than at present. 

Polar feedbacks

Hansen, Sato et al. find that current temperatures are at least as high as the Holocene Maximum (i.e., as high as they have been over the last 10,000 years).  They sum up: 

Earth at peak Holocene temperature is poised such that additional warming instigates large amplifying high-latitude feedbacks.  Mechanisms on the verge of being instigated include loss of Arctic sea ice, shrinkage of the Greenland ice sheet, loss of Antarctic ice shelves, and shrinkage of the Antarctic ice sheets.  These are not runaway feedbacks, but together they strongly amplify the impacts in polar regions of a positive (warming) climate forcing…  Augmentation of peak Holocene temperature by even +1 ºC would be sufficient to trigger powerful amplifying polar feedbacks, leading to a planet at least as warm as in the Eemian and Holsteinian periods, making ice sheet disintegration and large sea level rise inevitable.

[It is relevant here to note that warming in the pipeline due to thermal inertia, plus warming associated with the loss of aerosols, is greater than +1ºC.]

And during the Pliocene, with atmospheric greenhouse levels similar to today, the northern hemisphere was free of glaciers and ice sheets and beech trees grew in the Transantarctic Mountains. There are also strong indications that permanent El Nino conditions prevailed.

4d. Arctic carbon stores

As discussed above, scientists using radiometric dating techniques on Russian cave formations to measure historic melting rates going back 500,000 years conclude that a +1.5 ºC global rise in temperature compared to pre-industrial is enough to initiate widespread permafrost melt.  

In May this year, Brigham-Grette, Melles et al. published evidence from Lake El’gygytgyn, in north-east Arctic Russia, showing that 3.6–3.4 million years ago, summer mid-Pliocene temperatures locally were ~8 °C warmer than today, when CO2 was ~400 ppm.  This is highly significant because researchers including Celia Bitz and Philippe Ciais have previously found that the tipping point for the large-scale loss of permafrost carbon is around +8 ºC  to 10 ºC regional temperature increase.  Caias told the March 2009 Copenhagen climate science conference that: “A global average increase in air temperatures of +2 ºC and a few unusually hot years could see permafrost soil temperatures reach the +8 ºC threshold for releasing billions of tonnes of carbon dioxide and methane.” So, if the current level of greenhouse gases is enough to produce Arctic regional warming of ~+8 °C and that is a likely tipping point for large-scale permafrost loss, we have reached a disturbing milestone.

Even more disturbing is new research from Ballantyne, Axford et al. which says that during the Pliocene epoch, when CO2 levels were ~400 ppm, Arctic surface temperatures were 15–20 °C warmer than today’s surface temperatures. They suggest that much of the surface warming likely was due to ice-free conditions in the Arctic. Compared to the estimated tipping point for the large-scale loss of permafrost carbon of +8 ºC to 10 ºC regional warming, this research confirms both that the current level of greenhouse gases is sufficient to create both a sea-ice-free Arctic and Arctic warming more than sufficient to trigger large-scale loss of permafrost carbon.

Next post: Climate safety and the emissions reduction challenge 

http://www.climatecodered.org/2013/09/is-climate-change-already-dangerous-3.html