Why East Antarctica is warming more slowly than West Antarctica

[sinimod]

The following is a rather long post in which, if you have a pretty clear understanding of climate trends in Antarctica, I attempt to muddy the waters. If I have accomplished this, please let me down gently. Much of this comes from a short essay I wrote about a year ago on why parts of Antarctica has undergone some cooling. Since it is long, by necessity I must break it up into shorter posts as it causes an error to try to post the whole essay in one post.

Why are temperatures in East Antarctica warming slower than West Antarctica and the Antarctic Peninsula, or even cooling in places? The map below shows the trend in surface temperatures over the last couple of decades.

http://earthobservatory.nasa.gov/images/imagerecords/8000/8239/antarctica_avhrr_81-07.jpg

Map showing Antarctic Skin Temperature Trends between 1981 and 2007. Skin temperature is roughly the top one millimeter of land, sea, snow, or ice. Across most of the Antarctic the temperature increased, in some areas warming approaching 2 degrees Celsius during the period. The map is based on thermal infrared (heat) observations made by a series of National Oceanic and Atmospheric Administration satellite sensors. None of the sensors were in orbit at the same time, so scientists could not compare simultaneous observations from different sensors to make sure each was recording temperatures exactly the same. Instead, the team checked the satellite records against ground-based weather station data to inter-calibrate them and make the 26-year satellite record. The level of uncertainty is between 2 and 3 degrees Celsius. The most dramatic changes are the red areas associated with iceberg calving and the collapse of the Larsen B ice shelf. In these cases, the satellites saw a change from cold ice to relatively warm open water.

[sinimod]

West Antarctica is clearly warming at a faster rate than East Antarcica, which has been shown by some workers to have experienced cooling at some climate data stations. Doran et al. (2002; http://www.uic.edu/classes/geol/eaes102/Doran.pdf) point out that during the 20th Century global temperature warmed on average about 0.06°C per decade, but averaged about 0.19°C increase per decade from 1979 to 1998. Despite the increased rate of global warming during that time, they report that spatial analysis of Antarctic meteorological data demonstrates a net cooling on the Antarctic continent from 1966 to 2000, particularly during summer and autumn. The McMurdo Dry Valleys cooled 0.07°C per year between 1986 and 2000, with similar pronounced seasonal trends. Kwok and Comiso (2002; http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/8598/1/02-1151.pdf) point out that there has also been cooling recorded at the South Pole of 0.05°C per year from 1980 to 1999. At the Faraday Station on the Antarctic Peninsula, however, there has been a warming trend of 0.09°C per year from 1980 to 1999.

[sinimod]

Cooling in the interior of East Antarctica has been attributed to the increased tendency for the Southern Annular Mode (SAM) to exhibit a positive phase. In the positive phase of the SAM, the Southern Ocean westerlies, which make up the circumpolar vortex, strengthen, and weaken during the negative phase (Marshall, 2003; http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175/1520-0442(2003)016%3C4134:TITSAM%3E2.0.CO;2). Gillett et al. (2006; http://www.agu.org/pubs/crossref/2006/2006GL027721.shtml) gathered data from weather stations throughout the Southern Hemisphere (SH) and found that the positive phase of the SAM is associated with significant cooling over Antarctica… During the positive, or high index phase of the SAM, the circumpolar vortex produces a more effective blocking pattern which favors cooler tropospheric temperatures, particularly in East Antarctica according to Thompson and Solomon (2002; http://www.sciencemag.org/cgi/content/full/296/5569/895). They suggest that the loss of ozone over Antarctica, the ozone hole, has created a positive bias in the SAM, which has for decades, created the cooling tendency described above.

And the abstract of Gillett and Thompson (2003; http://www.sciencemag.org/cgi/content/abstract/302/5643/273 ):

Recent observations indicate that climate change over the high latitudes of the Southern Hemisphere is dominated by a strengthening of the circumpolar westerly flow that extends from the surface to the stratosphere. Here we demonstrate that the seasonality, structure, and amplitude of the observed climate trends are simulated in a state-of-the-art atmospheric model run with high vertical resolution that is forced solely by prescribed stratospheric ozone depletion. The results provide evidence that anthropogenic emissions of ozone-depleting gases have had a distinct impact on climate not only at stratospheric levels but at Earth's surface as well.

[sinimod]

Gillett and Thompson go on to say that the results in this study add to an increasing body of both observational (Thompson et al., 2004; Baldwin et al., 1999) and modeling (Boville, 1984; Polvani et al., 2001) evidence that suggests stratospheric processes play an important role in driving climate variability at the surface of the earth on a range of time scales, particularly at high latitudes. Observations reported in Thompson and Solomon (2002; http://www.sciencemag.org/cgi/content/abstract/296/5569/895) and Gillett and Thompson (2003; http://www.sciencemag.org/cgi/content/abstract/302/5643/273) strongly suggest that human emissions of ozone-depleting gases have demonstrably affected surface climate over the past few decades.

Shindell and Schmidt (2004; http://pubs.giss.nasa.gov/abstracts/2004/Shindell_Schmidt.html) have further found depleted ozone levels and greenhouse gases are contributing to cooler South Pole temperatures. They found that low ozone levels in the stratosphere and increasing greenhouse gases promote a positive phase of SAM. A positive SAM isolates colder air in the Antarctic interior. The study found higher ozone levels might have a reverse impact on the SAM, promoting a warming, negative phase. In this way, the effects of ozone and greenhouse gases on the SAM may cancel each other out in the future. This could nullify the SAM's affects and cause Antarctica to warm.

Arblaster and Meehl (2005, http://www.cgd.ucar.edu/ccr/publications/arblaster_meehl_sam.pdf) found that ozone changes are the biggest contributor to the observed summertime intensification of the southern polar vortex in the second half of the twentieth century. However, even as stratospheric ozone losses are expected to stabilize and eventually recover to preindustrial levels over the course of the twenty-first century, their results show that increasing greenhouse gases will continue to intensify the circumpolar vortex throughout the twenty-first century.

[sinimod]

However, Steig et al., (2009; http://www.nature.com/nature/journal/v457/n7228/full/nature07669.html),
using statistical climate-field-reconstruction techniques combined with independent data and satellite data for about the last couple of decades, suggest that the spatial and seasonal patterns of the observed temperature trends indicate that higher-order modes of atmospheric circulation, associated with regional sea-ice changes and radiative forcings have had a larger role in West Antarctica. Skeptics have complained that this applies only to surface temperatures and Steig et al. provide no tropospheric temperature data. However, However, Turner et al. (2006; http://www.sciencemag.org/cgi/content/abstract/311/5769/1914) offer evidence of mid tropospheric warming at a statistically significant rate of 0.5° to 0.7°Celsius per decade over the past 30 years. This has been confirmed by Bromwich et al. (2009; http://ams.confex.com/ams/10POLAR/techprogram/paper_152840.htm. Steig et al suggest that:Mean surface temperature trends in both West and East Antarctica are positive for 1957–2006, and the mean continental warming is comparable to that for the Southern Hemisphere as a whole..

It is certainly clear that warming on the Antarctic Peninsula has spread to the West Antarctica Ice Sheet at least as far as the Pine Island Bay-Thwaites Glacier region as described in earlier posts in Tony’s Antarctic Ice thread (Shepard et al., 2001, http://www.sciencemag.org/cgi/conten...t/291/5505/862; Rignot 2008, http://www.agu.org/pubs/crossref/200...GL033365.shtml; and Wingham et al. 2009, http://www.agu.org/pubs/crossref/200...GL039126.shtml).

[sinimod]

In addition, Turner (2004; http://www.scar.org/articles/elnino/El_Nino.pdf) has shown that the El Niño/La Niña cycle plays a significant role in shaping climate in Antarctica. El Niño Southern Oscillation (ENSO) signals are most likely transferred through the Rossby wave train (jet stream), which gives positive (negative) height anomalies over the Amundsen-Bellingshausen Sea during El Nino (La Nina) events.

The following are other potential teleconnections, all of which are highly variable and inconsistent, between ENSO and Antarctic climate (from Bromwich and Parrish, 1998; Turner, 2004). All of these teleconnections assume El Nino conditions, with La Nina conditions opposite these.

During El Nino events, surface winds are increased and surface temperatures are colder. Circumpolar westerlies are weaker and geopotential heights are higher. There are a diminished number of cyclones in the Circumpolar Trough (CPT, which is the same as the Circumpolar Vortex and the SAM), although amplified seasonal cycles create more meso-cyclones. The locations of these meso-cyclones invariably shift in location.

Mean sea level pressure (MSLP) anomalies change from positive to negative across the Southern Oscillation Index (SOI; the SOI is derived from the normalized difference in monthly atmospheric pressure between Tahiti and Darwin, Australia).

During El Nino, precipitation is generally lower, although the impacts are irregular and inconsistent and are generally strongest in West Antarctica. SSTs are higher in the Ross Sea and the sea ice area on the Ross Sea is typically reduced.

It is likely that ENSO variability can influence the SAM in the Southern Hemisphere summer (L'Heureux and Thompson, 2006; http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175/JCLI3617.1). Clearly ENSO is a major influence on the intensity of SAM and the climate of Antarctica.

[sinimod]

In summary, according to some authors, the SAM (CPV or CPT) has had major effects on Antarctic climate, particularly East Antarctica. The reduction in ozone and the creation of the ozone hole over Antarctica has strengthened the positive phase of the SAM, which these authors say have caused temperatures to cool over much of Antarctica. However, Steig et al suggest that the continent has warmed overall, particularly in West Antarctica, but including East Antarctica, and that the major influences have been regional changes in atmospheric circulation and associated changes in sea surface temperature and sea ice extent. ENSO plays a major role in Antarctic climate.

[sinimod]

As usual, I welcome any comments, corrections, and/or additions.

I guess I should have put a question mark at the end of my thread title.

[776281]

http://www.guardian.co.uk/environment/2009/nov/22/east-antarctic-ice-sheet-nasa

World's largest ice sheet melting faster than expected

The world's largest ice sheet has started to melt along its coastal fringes, raising fears that global sea levels will rise faster than scientists expected.

The East Antarctic ice sheet, which makes up three-quarters of the continent's 14,000 sq km, is losing around 57bn tonnes of ice a year into surrounding waters, according to a satellite survey of the region.

Satellite data from the whole of Antarctica show the region is now losing around 190bn tonnes of ice a year. Uncertainties in the measurements mean the true ice loss could be between 113bn and 267bn tonnes.

"If the current trend continues or gets worse, Antarctica could become the largest contributor to sea level rises in the world. It could start to lose more ice than Greenland within a few years," said Jianli Chen, of the University of Texas at Austin.

Donald Trump will be glad he kept the penthouse. Just because we do not know how high the wall of manure is, that is coming our way, does not mean that the wall of manure does not exist.

Science does not yet have all the answers, nor ever will, but we do know enough to know that we are in a lot of trouble.

Now to start reading some of sinimod's links

[sinimod]

As Tony has pointed out, the West Antarctic Ice Sheet could cause dramatic problems this century.

http://geology.com/research/images/antarctic-ice-instability-250.jpg

Concerns about stability. The ice sheet covering West Antarctica is the last great marine ice sheet. Its bed lies below sea level and slopes down inland from the coast. This profile is based on Thwaites Glacier, West Antarctica. In the top panel, the ice sheet is in equilibrium; influx from snowfall (q) is balanced by outflow. A small retreat (lower panel) will provoke changes in both the influx and the outflow. If these changes act to promote further retreat, the ice margin is unstable.

The West Antarctic Links to Sea-Level Estimation (WALSE) Workshop held in Austin, Texas in 2007(http://www.jsg.utexas.edu/walse/statement.html) had some stern warnings:

Satellite observations show that both the grounded ice sheet and the floating ice shelves of the Amundsen Sea Embayment have thinned over the last decades.

Ongoing thinning in the grounded ice sheet is already contributing to sea-level rise.

The thinning of the ice has occurred because melting beneath the ice shelves has increased, reducing the friction holding back the grounded ice sheet and causing faster flow.

Oceanic changes have caused the increased ice-shelf melting. The observed average warming of the global ocean has not yet notably affected the waters reaching the base of the ice shelves. However, recent changes in winds around Antarctica caused by human influence and/or natural variability may be changing ocean currents, moving warmer waters under the ice shelves.

Our understanding of ice-sheet flow suggests the possibility that too much melting beneath ice shelves will lead to “runaway” thinning of the grounded ice sheet. Current understanding is too limited to know whether, when, or how rapidly this might happen, but discussions at the meeting included the possibility of several feet of sea-level rise over a few centuries from changes in this region.

At the WALSE Workshop, a new hypothesis for the cause of rapid melting in the Amundsen Sea Embayment (http://geology.com/research/west-antarctic-ice-sheet.shtml)

The surface of Antarctica is so cold and the ice so thick that raising the region's air temperature a few degrees is not enough to cause significant melting. Instead, scientists have long suspected that warm water in the Amundsen Sea is flowing up under ice shelves—platforms of floating ice attached to the grounded ice sheet—and melting them from below. This increased melting speeds the flow of grounded ice sheet into the water.

But it's unlikely these warmer waters result directly from recent climate change. By measuring oxygen content, oceanographers have discovered that the warm water welling up below the glaciers has not been near the sea surface in the past few centuries. In oceanographer's terms, the water is “old.” It is part of a mass known as Circumpolar Deep Water connected to the North Atlantic through the globetrotting ocean conveyor belt. This water has been at depth for too long, scientists believe, for its temperature to reflect recent global warming.

Adrian Jenkins, a polar researcher from the British Antarctic Survey and WALSE participant, developed a computer model that showed a possible solution.

Antarctica is encircled by atmospheric currents that largely insulate it from the rest of Earth's climate and keep it colder than it otherwise would be. Jenkins' model showed that these circumpolar currents, sometimes called “Westerlies,” “the Screaming 50s,” or “the Roaring 40s,” actually push surface waters out away from the continent. This results from the Coriolis Force, the byproduct of Earth's rotation that causes cyclonic systems to turn counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. As surface water is pushed away, warm deep water rises to replace it.

If the atmospheric currents speed up, more water is pulled up. Indeed, observations indicate these atmospheric currents have sped up in recent decades in response to global warming. So increased upwelling seems likely.

The question is, what can be done about it?

[sinimod]

Here is another attempt at showing the image I wanted to show in the last post. It is a cartoon cross section of the West Antarctic Ice Sheet showing how it is below sea level and how that could be a mechanism for its instability. Here is my second attempt at the image:

http://geology.com/research/images/antarctic-ice-instability-250.jpg

Caption:
Concerns about stability. The ice sheet covering West Antarctica is the last great marine ice sheet. Its bed lies below sea level and slopes down inland from the coast. This profile is based on Thwaites Glacier, West Antarctica. In the top panel, the ice sheet is in equilibrium; influx from snowfall (q) is balanced by outflow. A small retreat (lower panel) will provoke changes in both the influx and the outflow. If these changes act to promote further retreat, the ice margin is unstable.

(Well, it works on the Preview Post.)

[sinimod]

Crap! Just go to the article: http://geology.com/research/west-antarctic-ice-sheet.shtml

[sinimod]

That's weird, the image I posted in the next to last and 3rd to last posts didn't show up earlier, but now it does. Anyway, I am glad the image shows up now. It shows an unsettling diagram of how unstable the WAIS could be, as the grounding line is below sea level. With warmer water coming in contact with the ice, melting it from below, it will begin to seep below the ice sheet, creating more instability and possibly dramatically increased ice flow.

[sinimod]

Another factor that affects the climate change of East and West Antarctica differently has to do with their differing topography. Nicolas and Bromwich (2009; http://ams.confex.com/ams/10POLAR/techprogram/paper_152819.htm) state:

In East Antarctica, high interior elevations and steep coastal slopes usually confine ocean air masses to the immediate coastal regions. With relatively lower elevations, West Antarctica (WA) exhibits a more ocean-influenced climate as offshore air masses more easily penetrate inland.

As evidenced by the distribution of mean annual and seasonal precipitation and potential temperature, ocean influence is constrained by the major topographic divides of WA, with the Amundsen/Bellingshausen Sea (ABS) sector being most affected. Advection of heat and moisture across WA does occur frequently and is associated with depressions moving over the ABS. This transport is found to be greatest in wintertime, at the peak of cyclonic activity over the Southern Ocean, and shifts in longitude with the location of depressions.

The map below shows the location of the Amundsen/Bellingshausen Sea sector:

http://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/AmundsenSea.jpg/800px-AmundsenSea.jpg

I suspect the Transantarctic Mountains, being the largest topographic divide on the continent, provide a barrier to the circulation of these air masses into East Antarctica from the west. As can be clearly seen on the surface temperature trend map of Antarctica, the amount of temperature change is significantly different on the west and east sides of the Transantarctic Mountains, with more warming occurring on the west side than on the east.

http://upload.wikimedia.org/wikipedia/commons/9/99/Antarctic_Temperature_Trend_1981-2007.jpg

[sinimod]

NASA has a short piece on Antarctica melting. In this piece there is a brief description of, among other things, the differences between East and West Antarctica.

http://www.nasa.gov/topics/earth/features/20100108_Is_Antarctica_Melting.html

Two-thirds of Antarctica is a high, cold desert. Known as East Antarctica, this section has an average altitude of about 2 kilometer (1.2 miles)...

West Antarctica is very different. Instead of a single continent, it is a series of islands covered by ice

...much of the West Antarctic Ice Sheet (WAIS, in the jargon) is actually sitting on the floor of the Southern Ocean, not on dry land. Parts of it are more than 1.7 kilometer (1 mile) below sea level.

This summer, a British group revisited the Pine Island Glacier finding and found that its rate of retreat had quadrupled between 1995 and 2006.

it took just three weeks to crumble a 12,000-year old ice shelf. (about the crumbling of the Larsen B ice shelf. It's just another striking bit of evidence that things are not normal - a 12,000 year old ice shelf breaking up. It certainly didn't break up during the Medieval Climate Anomaly.)

Michael Schodlok, a JPL scientist who models the way ice shelves and the ocean interact, says melting of the underside of the shelf is a pre-requisite to these collapses. (pretty clear evidence of the warming of southern ocean water)

[sinimod]

Earlier it was discussed how significant portions of the subglacial topography of West Antarctica is actually below sea level and that in East Antarctica “high interior elevations and steep coastal slopes usually confine ocean air masses to the immediate coastal regions.” (from Nicholas and Bromwich, 2009). However, recent work by a multinational survey called ICECAP (includes the British Antarctic Survey, Australian Antarctic Division, and the University of Texas; ICECAP is an acronym meaning ‘Investigating the Cryospheric Evolution of the Central Antarctic Plate’), which uses ice-penetrating radar and other sensors flown on aircraft to map the subglacial topography, has discovered that the subglacial topography of East Antarctica’s Wilkes Basin is far lower than previously thought, with two long troughs plunging as far as 1,400 meters below sea level. (Fox, 2010, Science Magazine, v. 328, p. 1630-1631 (”http://www.sciencemag.org/cgi/content/short/328/5986/1630”) [just 1st paragraph of news article in Science Magazine]).

In addition, findings show that the much larger Aurora Basin, which includes the Totten Glacier (which is apparently losing 1.9 meters of thickness per year), is connected to the ocean by troughs that sit 500 to 1000 meters below sea level. These troughs deepen as they head inland, to as low as 2000 meters below sea level in one spot. This produces the possibility of the classic scenario where melting causes the grounding line of the ice sheet to deepen, making it more susceptible to further retreat. Bottom line here, this area is potentially much more susceptible to climate change than had been previously thought.

The figure below is a 2008 version of the subglacial topography of Antarctica. Note that the much of the Aurora and Wilkes Basins (located in the SE Quadrant of this map just east of the lower portion of the Transantarctic Mountains) are below sea level. Some areas in the Wilkes Basin will be deepened with the addition of the ICECAP data.

http://upload.wikimedia.org/wikipedia/commons/thumb/b/b7/AntarcticBedrock.jpg/600px-AntarcticBedrock.jpg

Patterns of thinning in the Totten Glacier suggest that its movement may have accelerated near the ice front. This thinning may also be the case for nearby Vanderford Glacier, causing the glaciers to stretch. A study (http://www.nature.com/ngeo/journal/v2/n12/full/ngeo694.html) by gravity-sensing GRACE satellites along the East Antarctic coast found that two areas are losing 13 km^3 per year. However, it must be noted that ice loss from these areas is still far less than the 150 km^3 being lost from West Antarctica each year. But the currently unanswered question is: if there are deep basins around the edges of the continent that models haven’t considered, then are scientists underestimating the potential for retreat?

In the article by Fox, the scientists at ICECAP ask the big question: with the expected concentrations of atmospheric CO2 in 2100, could ice loss, in the coming centuries, cause sea level rise to reach levels experienced in the Middle Pliocene when sea levels are thought to have been as much as 35 meters higher than today? Scientists think it is possible for CO2 levels to reach that experienced in the Middle Pliocene by 2100.

[sinimod]

Here (http://www.sciencemag.org/cgi/content/summary/328/5986/1630) is another attempt to link to the Fox abstract in Science Magazine.

[sinimod]

New Map Reveals Giant Fjords Beneath East Antarctic Ice Sheet (http://www.nsf.gov/news/news_summ.jsp?cntn_id=119718&org=NSF&from=news)

Scientists from the United States, United Kingdom and Australia have used ice-penetrating radar to create the first high-resolution topographic map of one of the last uncharted regions of Earth, the Aurora Subglacial Basin, an immense ice-buried lowland larger than Texas in East Antarctica.

The map reveals some of the largest fjords or ice cut channels on Earth, providing important insights into the history of ice in Antarctica.

Data from the study will help computer modelers improve their simulations of the Antarctic ice sheet and its potential impact on global sea level.

Because the basin lies kilometers below sea level, seawater could penetrate beneath the ice, causing portions of the ice sheet to collapse and float off to sea. Indeed, this work shows that the ice sheet has been significantly smaller in the past.