Showing posts with label East Antarctica. Show all posts

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Joe Romm: Coastal studies experts: “For coastal management purposes, a [sea level] rise of 7 feet (2 meters) should be utilized for planning major infrastructure.” Front-page New York Times piece on sea level rise gets it mostly right


Coastal studies experts: “For coastal management purposes, a [sea level] rise of 7 feet (2 meters) should be utilized for planning major infrastructure”

Front-page NY Times piece on sea level rise gets it mostly right


by Joseph Romm, Climate Progress, November 14, 2010

The New York Times has a splashy front-page story on some of the latest research on sea level rise today.  The graphics above make clear the paper gets a big part of the story right — the latest science says we are facing 3-6 feet of sea level rise this century.

Kudos to the NYT for featuring such an important story.  Given that serious federal climate action is unlikely for years if not a decade or more, it is more incumbent on the media than ever to explain to the public what’s coming.

The story has its flaws, though.  For some reason the media — and many scientists — seem constitutionally incapable of explaining that inaction makes things much worse, that inaction greatly increases the chances of the worst impacts.  The NYT has usefully cited the work of Rahmstorf, but somewhat simplified and hence sanitized his graph:

SLR PNAS pic
Our current do-nothing or do-little path currently matches the A1F1 scenario (see “U.S. media largely ignores latest warning from climate scientists: “Recent observations confirm … the worst-case IPCC scenario trajectories (or even worse) are being realised” — 1000 ppm“), where the midpoint SLR projection is nearly 5 feet.  That’s no surprise since the unrestricted emissions scenario can leads to a staggering warming where the ice is located (see M.I.T. doubles its 2095 warming projection to 10 °F — with 866 ppm and Arctic warming of 20 °F).

So it is a tad frustrating that the NYT buries this crucial point in the final two paragraphs of this long article:
Climate scientists note that while the science of studying ice may be progressing slowly, the world’s emissions of heat-trapping gases are not. They worry that the way things are going, extensive melting of land ice may become inevitable before political leaders find a way to limit the gases, and before scientists even realize such a point of no return has been passed. 
“The past clearly shows that sea-level rise is getting faster and faster the warmer it gets,” Dr. Rahmstorf said. “Why should that process stop? If it gets warmer, ice will melt faster.”
The key point is that we are woefully prepared for what is likely to come:
“I think we need immediately to begin thinking about our coastal cities — how are we going to protect them?” said John A. Church, an Australian scientist who is a leading expert on sea level. “We can’t afford to protect everything. We will have to abandon some areas.”
Duh.  Triage.  It’s coming.

This NYT article give the answer to the question I posed Friday – AGU Climate Q&A Service won’t answer this Q: “Is current U.S. infrastructure adequate for sea level rise?” Is that prudent — or lame?

Key West and Galveston and probably New Orleans appear unsavable on our current emissions path, but what about Miami and Houston?  I’ll do a post on that subject later.

What should people plan for?  Obviously, it makes no sense to plan for the best case.  Most people are highly risk averse and spend a considerable amount of money planning for worst-case scenarios — that’s why they buy fire insurance and catastrophic health insurance.  Military and epidemiological planners routinely focus vast amounts of time and money around the worst-case scenarios.

Even if seas only rise, say 4 feet by 2100, then sea levels are likely to be rising 6 inches a decade or more at that point, probably for centuries, so again it makes little sense to plan for, say 2-3 feet of SLR, particularly when making big investments like, say, a new sewage treatment plant (or a major upgrade to an old one), which is going to last a very long time and not going to be easy to move.

As an aside, a 2009 study in Geophysical Research Letters found that “If Greenland’s ice melts at moderate to high rates, ocean circulation by 2100 may shift and cause sea levels off the northeast coast of North America to rise by about 12-20 inches (about 30-50 cm) more than in other coastal areas” (see here).
The NYT article notes:
One of the deans of American coastal studies, Orrin H. Pilkey of Duke University, is advising coastal communities to plan for a rise of at least five feet by 2100.
Since the NYT didn’t include a direct link to that claim or a direct quote, I went looking on Google, which turned up this op-ed piece from last November by Pilkey, “Rising sea levels: a strategy for N.C.“:
DURHAM — Western Carolina University’s Rob Young and I have argued that seas will rise at least 3 feet in this century and that, for coastal management purposes, a rise of 7 feet (2 meters) should be utilized for planning major infrastructure.
I have emailed Pilkey to find out the source of that discrepancy, but for now, I’m going with this as the headline quote.

I have three more issues with the article.  First, while the gratuitous quotes from the anti-science disinformers were kept to a minimum, the NYT should at least try to quote disinformers with relevant expertise:
Global warming skeptics, on the other hand, contend that any changes occurring in the ice sheets are probably due to natural climate variability, not to greenhouse gases released by humans… 
John R. Christy, a climatologist at the University of Alabama in Huntsville who is often critical of mainstream climate science, said he suspected that the changes in Greenland were linked to this natural variability, and added that he doubted that the pace would accelerate as much as his colleagues feared. 
For high predictions of sea-level rise to be correct, “some big chunks of the Greenland ice sheet are going to have to melt, and they’re just not melting that way right now,” Dr. Christy said.
As the link the NYT provides makes clear, Christy has no publications in this area.  His ‘expertise’  is in temperature trends and satellite measurements, but even there, how many times one has to be wrong before the media stops quoting you? (see “Should you believe anything John Christy and Roy Spencer say?“).

Second, the NYT asserts:
Certain measurements are so spotty for Antarctica that scientists have not been able to figure out whether the continent is losing or gaining ice.
In fact, while all such measurements have uncertainty, the literature is pretty clear that Antarctica has been losing mass in the past decade — at an accelerating rate, as Skeptical Science explains:
Figure 2 shows the ice mass changes in Antarctica for the period April 2002 to February 2009 (Velicogna 2009) . The blue line/crosses show the unfiltered, monthly values. The red crosses have seasonal variability removed. The green line is the best fitting trend.


Figure 2. Ice mass changes for the Antarctic ice sheet from April 2002 to February 2009. Unfiltered data are blue crosses. Data filtered for the seasonal dependence are red crosses. The best-fitting quadratic trend is shown as the green line (Velicogna 2009). 
With the longer time series, a statistically significant trend now emerges. Not only is Antarctica losing land ice, the ice loss is accelerating at a rate of 26 Gigatonnes/yr2 (in other words, every year, the rate of ice loss is increasing by 26 Gigatonnes per year). It turns out that since 2006, East Antarctica has no longer been in mass balance but is in fact, losing ice mass (Chen 2009). This is a surprising result as East Antarctica has been considered stable because the region is so cold. This indicates the East Antarctic ice sheet is more dynamic than previously thought. 
This is significant because East Antarctica contains much more ice than West Antarctica. East Antarctica contains enough ice to raise global sea levels by 50-60 metres while West Antarctica would contribute around 6-7 metres. The Antarctic ice sheet plays an important role in the total contribution to sea level. That contribution is continuously and rapidly growing.
I wrote about the Chen paper here (see Satellite data stunner: “Our data suggest that EAST Antarctica is losing mass…. Antarctica may soon be contributing significantly more to global sea-level rise”).  The study begins, “Accurate quantification of Antarctic ice-sheet mass balance and its contribution to global sea-level rise remains challenging, because in situ measurements over both space and time are sparse,” and it concludes:
Our results suggest that over the WAIS [West Antarctic ice sheet] (especially the ASE [Amundsen Sea Embayment]) there is accelerated ice loss since around 2005 and/or 2006, with the EAIS showing correlated changes of the same sign in this period, attributed to increased ice loss over EAIS coastal regions in recent years. Using a simple linear projection for the period 2006–2009, Antarctic ice loss rate can be as large as -220plusminus89 Gt yr-1. These new GRACE estimates, on average, are consistent with recent InSAR fluxes but, in contrast to previous estimates, they indicate that as a whole, Antarctica may soon be contributing significantly more to global sea-level rise.
Yes, a recent paper has questioned the full magnitude of some of the GRACE ice losses, but many leading experts have in turn questioned that work.  I suppose I will have to do a post on that.

Notwithstanding the NYT, the best science says that Antarctica is losing ice, and the ice loss is accelerating.

Third, one of the most puzzling statements in the entire piece is this:
The information problems are even more severe in Antarctica. Much of that continent is colder than Greenland, and its ice sheet is believed to be more stable, over all. But in recent years, parts of the ice sheet have started to flow rapidly, raising the possibility that it will destabilize in the same way that much of the world’s other ice has.
Notwithstanding the phrase “over all,” the WAIS has long been known it to be unstable, as the West Antarctic Ice Sheet Initiative explains at length here. As I wrote in the “high water” part of my book:
Perhaps the most important, and worrisome, fact about the WAIS is that it is fundamentally far less stable than the Greenland ice sheet because most of it is grounded far below sea level. The WAIS rests on bedrock as deep as two kilometers underwater. One 2004 NASA-led study found that most of the glaciers they were studying “flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates, providing exit routes for ice from further inland if ice-sheet collapse is under way.” A 2002 study in Science examined the underwater grounding lines–the points where the ice starts floating. Using satellites, the researchers determined that “bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed.” And that melt rate is positively correlated with ocean temperature. 
The warmer it gets, the more unstable WAIS outlet glaciers will become. Since so much of the ice sheet is grounded underwater, rising sea levels may have the effect of lifting the sheets, allowing more-and increasingly warmer-water underneath it, leading to further bottom melting, more ice shelf disintegration, accelerated glacial flow, and further sea level rise, and so on and on, another vicious cycle. The combination of global warming and accelerating sea level rise from Greenland could be the trigger for catastrophic collapse in the WAIS.
And the WAIS Initiative notes:
A final, disturbing extension of West Antarctic collapse is that a substantial portion of the much-larger East Antarctic ice sheet would likely drain through the gap in the Transantarctic Mountains now occupied by the West Antarctic ice sheet. This would only increase the eventual magnitude of the change in sea level, further exacerbating the calamity.
So we have a cascading effect from Greenland to WAIS to EAIS.

For the record, a 2009 study in Science found that sea level rise from a collapse of the WAIS would likely be 25% higher for North America than previously estimated:
The catastrophic increase in sea level, already projected to average between 16 and 17 feet around the world, would be almost 21 feet in such places as Washington, D.C., scientists say, putting it largely underwater. Many coastal areas would be devastated. Much of Southern Florida would disappear.
And the WAIS is already in danger now:
So, yes, we can all hope that humanity somehow quickly becomes smart enough to stay at or below 450 ppm, and then returns to 350 ppm as quickly as possible, keeping overall sea level rise to below 3 feet this century.  But prudent planners should plan on 5-7 feet of SLR over the next 100 years.

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Western Australia drought is possibly the worst for the past 750 years

WA drought 'could be worst for 750 years'

by CHALPAT SONT, Western Australia Today, February 9, 2010
Scientists have made a surprising link between climate patterns in Australia and Antarctica. Scientists have made a surprising link between climate patterns in Australia and Antarctica.

If you thought the drought affecting south-west WA since the 1970s was extreme, you were right.
But just how extreme has been a matter of contention.

Now, scientists believe it could be the worst of its kind in 750 years, after making an unexpected discovery.
Researchers from the Australian Antarctic Division and Antarctic Climate and Ecosystems Co-operative Research Centre have identified a link between the drought, which began in the early 1970s, and snowfall at a site in East Antarctica over the same period.

In research published in Nature Geoscience, they say the relationship is inverse:  high snowfalls at the Law Dome site correlate with low rain in the South-West.

This is a result of the atmospheric circulation pattern that brings dry, cool air to Australia, while sending warm, moist air to East Antarctica.

However, the high snowfall at Law Dome was unlike any other in the past 750 years, and led the researchers to believe the drought was similarly unusual.

Since the 1970s, there has been a decline of up to 20% in winter rainfall in the South-West and, though the cause of the drought remains unclear, others have pointed to land-use changes, ocean temperatures, air circulation changes and natural variability.

But its severity has been hard to calculate, with weather records going back only about 100 years, and the oldest tree-ring record, 350 years, from a site that has not been affected by the drought.

The researchers found that the snowfall was of a severity expected only once in every 38,000 years.

Adjusting their analysis of ice cores, it still should happen only about every 5400 years.

"It also suggests ... that if the mix of factors that influence [South-West] rainfall over the past century reflects that of the longer term, then the recent drought ... may be similarly unusual," the researchers say.

Lead researcher Tas van Ommen said the results of the study were unexpected.

"We were surprised at first, given the complexity of climate processes, to find such a direct connection between our ice core and the climate of Western Australia," he said.

"By identifying new processes that influence regional Australian climate, this work offers the possibility to improve understanding and reduce uncertainty in future projections of climate change.

"This work underscores the need for long-term records of past climate from sources like ice cores and it illustrates the important role that Antarctic climate processes play globally."

It suggested human influence was likely to have played a role in the drought, Dr van Ommen said.

University of NSW professor Andy Pitman said the study was a "good and bad news story."

"It is good for those policy makers in WA who invested in alternative sources of water based on earlier research by CSIRO and Bureau of Meteorology," he said.

"This new science suggests they made a wise decision. It is, of course, less good news for the future of water dependent industries in WA and reinforces the urgent need for global cuts in greenhouse gas emissions."

Monash University professor Neville Nicholls said the researchers may even have underestimated the severity of the drought.

"Since about 1990, snowfall at their site in Antarctica appears to have decreased, but the South-West rainfall has not rebounded as we might have expected from this," he said.

"This indicates that some additional mechanism is affecting either snowfall or the drought. This is not surprising in a time of strong global warming. But we do need to work out these mechanisms."

Link:  http://www.watoday.com.au/environment/climate-change/wa-drought-could-be-worst-for-750-years-20100205-niee.html

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A. K. Tripati, C. D. Roberts & R. A. Eagle, Science 326 (2009), Coupling of CO2 and ice sheet stability over major climate transitions of the last 20 million years

Science, (4 December 2009) Vol. 326, No. 5958, pp. 1394-1397; DOI: 10.1126/science.1178296

Coupling of CO2 and ice sheet stability over major climate transitions of the last 20 million years

Aradhna K. Tripati* (Departments of Earth and Space Sciences and Atmospheric and Oceanic Sciences, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, U.S.A.;  Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, U.K.), Christopher D. Roberts (Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, U.K.), and Robert A. Eagle (Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, U.S.A.)

Abstract

The carbon dioxide (CO2) content of the atmosphere has varied cyclically between ~180 and ~280 parts per million by volume over the past 800,000 years, closely coupled with temperature and sea level. For earlier periods in Earth’s history, the partial pressure of CO2 (pCO2) is much less certain, and the relation between pCO2 and climate remains poorly constrained. We use boron/calcium ratios in foraminifera to estimate pCO2 during major climate transitions of the past 20 million years. During the Middle Miocene, when temperatures were ~3° to 6°C warmer and sea level was 25 to 40 meters higher than at present, pCO2 appears to have been similar to modern levels. Decreases in pCO2 were apparently synchronous with major episodes of glacial expansion during the Middle Miocene (~14 to 10 million years ago) and Late Pliocene (~3.3 to 2.4 million years ago).

*Correspondence e-mail: ripple@zephyr.ess.ucla.edu

Link to abstract:  http://www.sciencemag.org/cgi/content/abstract/326/5958/1394

Excerpt:

These results provide some constraints on pCO2 thresholds for the advance and retreat of continental ice sheets in the past, which is also relevant in the context of anthropogenic climate change because it is uncertain how continental ice sheets will respond over the coming centuries to increased levels of pCO2 (1). By comparing our reconstruction to the published data sets described above, we are able to estimate past thresholds for the buildup of ice in different regions. When pCO2 levels were last similar to modern values (that is, greater than 350 to 400 ppmv), there was little glacial ice on land or sea ice in the Arctic, and a marine-based ice mass on Antarctica was not viable. A sea ice cap on the Arctic Ocean and a large permanent ice sheet were maintained on East Antarctica when pCO2 values fell below this threshold. Lower levels were necessary for the growth of large ice masses on West Antarctica (~250 to 300 ppmv) and Greenland (~220 to 260 ppmv). These values are lower than those indicated by a recent modeling study, which suggested that the threshold on East Antarctica may have been three times greater than in the Northern Hemisphere (35).

This work may support a relatively high climate sensitivity to pCO2. pCO2 values associated with major climate transitions of the past 20 Ma are similar to modern levels. During the Mid-Miocene, when pCO2 was apparently grossly similar to modern levels, global surface temperatures were, on average, 3-6 °C warmer than in the present (2, 25). We suggest that the Mid-Miocene may be a useful interval to study to understand what effect sustained high pCO2 levels (i.e., a climate in equilibrium with near-modern pCO2 values) may have on climate.

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Richard Black of the BBC: East Antarctic ice sheet may be losing mass

East Antarctic ice sheet may be losing mass

by Richard Black, Environment correspondent, BBC News website, November 22, 2009

Antarctic coast
The mass loss is probably driven by processes occurring on the coast

The East Antarctic ice sheet has been losing mass for the last three years, according to an analysis of data from a gravity-measuring satellite mission.

The scientists involved say they are "surprised" by the finding, because the giant East Antarctic sheet, unlike the west, has been thought to be stable.

Other scientists say ice loss could not yet be pinned on climate change, and uncertainties in the data are large.
The US-based team reports its findings in the journal Nature Geoscience.

The data comes from NASA's Gravity Recovery and Climate Experiment (GRACE) mission.
It energises me as a scientist, but I'm not convinced that as yet it should energise anyone else
Professor Richard Alley
GRACE has previously shown that the smaller West Antarctic and Greenland ice sheets are losing mass.

These two bodies of ice contain enough water to raise sea levels by about 6-7 m (20 ft.) each if they melted completely.

Melting the East Antarctic sheet would raise sea levels by much more -- about 50-60 m.

But scientists have generally discounted the possibility of it happening because the region is so cold.

The GRACE measurements suggest there was no net ice loss between 2002 and 2006.
Antarctica (BBC)

But since then, East Antarctica has been losing 57 billion tonnes (Gt) per year.

"We felt surprised to see this change in East Antarctica," study leader Jianli Chen from the Centre for Space Research at the University of Texas in Austin told BBC News.

The loss still looks small by contrast with West Antarctica, which is losing 132 Gt per year, and with Greenland, where a recent analysis combining GRACE data with other measurements indicated an annual figure of 273 Gt.

Previous GRACE analyses -- and those from other satellites -- had given an inconclusive picture for the giant ice body.

The twin GRACE satellites fly in close formation, detecting minute changes in the Earth's gravity through the marginal changes this causes in their relative positions.

Eastern energy
Measuring Antarctic ice loss is a tricky issue because the continent itself is rising and deforming.
East Antarctic ice - graphic
Its ice cover was significantly thicker during the last Ice Age; as the ice melted, the weight pressing down on the rock abated, and the rock is "isostatically rebounding."

Readings from satellite missions have to be adjusted to allow for this rebound -- and that is one source of uncertainty when trying to assess the significance of the new research, according to Richard Alley, one of the world's leading glaciologists.

"The first thing is that lots of this is dependent on the isostatic [rebound] model, and (recent work has) cast some doubt on the istostatic models that people are using," commented the Penn State University researcher (who was not involved in the paper).

"And then you get into the age-old question of 'is it climate or is it weather?"

"So it energises me as a scientist, but I'm not convinced that as yet it should energise anyone else."

Rising potential
The GRACE data gives a picture of where ice is being lost across the continent; and these areas are mainly on the coast.

It is not clear what physical processes could be driving any loss of mass here, although it is not simply melting due to high air temperatures, because temperatures are well below zero.

One clue could lie in research published last year by Leigh Stearns and colleagues, showing that lakes under the ice sheet can periodically overflow, with the liquid water then acting as a lubricant to speed glaciers on their way towards the sea.
Artist's impression of Grace satellite in orbit
The Grace satellites provide a twin eye on gravity at the Earth's surface

Commenting on the new research, Dr Stearns told BBC News: "In these coastal regions the ice loss could be driven by some interaction with the oceans or some weather patterns, or it could be a sub-glacial lake that drained and caused some thinning -- so it might not be climate-related.

"It's easy to jump to the conclusion that it's exceptional because it's the first time we've recorded it, but we do need a baseline of how things have been in the past so we do need to be cautious," said the University of Kansas researcher.

"Nevertheless, it awakens us to the fact that the East Antarctic sheet is more dynamic than we thought, and we do need to pay attention to it because its potential for sea level rise is so much greater than in West Antarctica or Greenland."

Dr Chen said that one of his team was currently conducting airborne surveys of one of the regions where mass loss had been detected, hoping to shed some light on the mechanisms involved.

Link:  http://news.bbc.co.uk/2/hi/science/nature/8371773.stm

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J. L. Chen, C. R. Wilson, D. Blankenship & B. D. Tapley, Nature Geosci., Accelerated Antarctic ice loss from satellite gravity measurements

Nature Geoscience, published online 22 November 2009; doi: 10.1038/ngeo694 

Accelerated Antarctic ice loss from satellite gravity measurements

J. L. Chen* (Center for Space Research, University of Texas at Austin, Austin, TX 78759, U.S.A.), C. R. Wilson (Center for Space Research, University of Texas at Austin, Austin, TX 78759; Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712, U.S.A.), D. Blankenship (Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712, U.S.A.) and B. D. Tapley (Center for Space Research, University of Texas at Austin, Austin, TX 78759, U.S.A.)

Abstract

Accurate quantification of Antarctic ice-sheet mass balance and its contribution to global sea-level rise remains challenging, because in situ measurements over both space and time are sparse. Satellite remote-sensing data of ice elevations and ice motion show significant ice loss in the range of -31 to -196 Gt yr-1 in West Antarctica in recent years1, 2, 3, 4, whereas East Antarctica seems to remain in balance or slightly gain mass1, 2, 4, with estimated rates of mass change in the range of -4 to 22 Gt yr-1. The Gravity Recovery and Climate Experiment5 (GRACE) offers the opportunity of quantifying polar ice-sheet mass balance from a different perspective6, 7. Here we use an extended record of GRACE data spanning the period April 2002 to January 2009 to quantify the rates of Antarctic ice loss. In agreement with an independent earlier assessment4, we estimate a total loss of 190plusminus77 Gt yr-1, with 132plusminus26 Gt yr-1 coming from West Antarctica. However, in contrast with previous GRACE estimates, our data suggest that East Antarctica is losing mass, mostly in coastal regions, at a rate of -57plusminus52 Gt yr-1, apparently caused by increased ice loss since the year 2006.

*Correspondence e-mail: chen@csr.utexas.edu

Link to abstract:  http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo694.html

Hat tip: Paolo Morelli

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Tim Naish: Evidence for anthropogenic climate change is unassailable

Unassailable Evidence

Published by RedLogix on July 8, 2009 at 6:00 am in climate change.100 Comments
Tim Naish

Tim Naish

Inaugural Lectures are very traditional university events, held these days to permit outstanding researchers to present an overview of their work to the wider academic community and public. Last night Prof. Tim Naish delivered a clear and decisive verdict about human-induced climate change: the evidence is unassailable.

Held in the very formal surrounds of the Hunter Building Council Chambers, the room was full to what I would guess its capacity of 400-500 people. His presentation wove together threads of the science, his own career, acknowlegements to those who went before him and the numerous mentors and colleagues whom all modern researchers depend on. Modern science is a very complex business; while the rare lone genius occasionally contributes ground-breaking insights, the vast bulk of progress these days is made by teams of people supporting each other, and all standing on the shoulders of those who went before them.

Starting with the Scottish mathemetician James Croll (1870), who was the first to deduce and calculate what are now more popularly known as the Milankovitch (1930s) cycles, Naish gave a brief introduction to the naturally occurring Ice Ages and sea-level changes that accompany them. The next major figure referenced was Sir Nicholas Shackleton (1937-2006), a pioneer in the use of mass spectrometry to determine changes in climate as recorded in the oxygen isotope composition of calcareous microfossils. Using ocean sediment cores, his team convincingly demonstrated that oscillations in climate over the past few million years could be correlated with variations in the orbital and positional relationship between the Earth and the Sun. However, even late in his life, Shackleton realised that the underpinning ideas of his work were only theoretical, that corroborating physical evidence was still required.

Tim Naish’s PhD work (1980s) studying sedimentary sequences in the Wanganui basin provided that evidence. The Wangaui basin is a 5-km-deep depression in the earth’s crust that has been filled over millions of years with erosion material from the continuously uplifting Southern Alps, material that is driven north up the West Coast by part of the Great Oceanic conveyor currents to form layer upon layer of beach material in the basin. Within that record is embedded clear evidence of numerous, dramatic sea-level changes, often in the order of 50-100 m, that exactly correlate with Shackleton’s records. Subsequent work has detailed a precise and robust sequence of almost 100 such oscillations, going back millions of years.

After working for Bob Carter for a number of years, Naish joined GNS (Geologic and Nuclear Sciences CRI based in Seaview Lower Hutt and closely attached to Victoria University), initially as a petroleum geologist. Very quickly he became involved in various Antarctic drilling programs, the first at Cape Roberts. This last summer, he was the Science Team leader for the ANDRILL project, an ambitious and successful core drill sited on the Ross Sea Ice shelf. Essentially, the drill penetrated 80 m of floating ice, 800 m to the sea bed, and then another 1000 m into the sedimetary layers beneath. (This alone was a remarkable technical tour-de-force and currently a world record.)

Most such core drills only recover about 40% of the potential record, but a specialist New Zealand company has pioneered innovative techniques allowing them to recover 98% of the material, greatly enhancing the quality of the data that can be derived from them. In the 2007-2008 season, the team’s sedimentologists identified 60 cycles when ice sheets or glaciers advanced and retreated across McMurdo Sound, dating back at least 5 million years.

Now for the takeaway message.

Over the last 3 million years, the Earth’s climate has undergone at least 60 naturally driven Ice Age cycles, each accompanied by major changes in sea level. As the temperature changes, so does the CO2 level. Over very long time scales, it is apparent that the Earth is gradually cooling, but the amplitude of the cycle changes is of the same order, i.e., the peak warm periods are almost as warm as they were million years ago, before gradually sinking back into the next Ice Age. Critically, it is vital to understand that the warm peaks of this natural glacial cycle always coincide with a peak CO2 level of not more than 300 ppm. [Blogger's note: we are pretty much at 390 ppm, now.]

Normally, these changes take place over many tens of thousands of years. Humans, however, have taken CO2 from about 280 ppm pre-Industrial to almost 400 ppm in around 100 years. In geological/climatic terms, this time scale is less than an eye-blink; it is a massive, virtually instantaneous, shock to the system. The last time the Earth’s climate had this much CO2 in it was about 3 million years ago when the climate was 5-6 °C warmer, there was no ice at either pole, and sea level was about 100 m higher than present. The major reason why this has not already happened is that the oceans represent a monstrous thermal mass, and the time lag for them to respond will be in the order of many hundreds of years, but respond they inevitably will. And it is the warming oceans that melt the Antarctic Ice shelves.

The ANDRILL sediments clearly show that during the warm periods the Antarctic oceans were full of algae blooms and the sea temperature was at least 5 °C. No ice existed in Antarctica during these warm inter-glacial periods. None at all.

There are two Antarctic ice shelves. The Eastern Ice shelf (EAIS) is by far the larger, grounded mostly above sea level and considered relatively stable for the foreseeable future. The West Antarctic Ice Shelf (WAIS) is totally different. Much of it is grounded at depths of 1-2 km below sea level. Therefore, it is peculiarly exposed to the effects of warming oceans in a potentially unstable and difficult to predict fashion.

The current IPCC’s mainstream predictions are of a 0.5 m sea-level rise by 2100, and exclude melting of the Greenland ice sheet and WAIS because at the time of publishing the IPCC considered the science around them too uncertain. The ANDRILL work has greatly reduced one aspect of that uncertainty. Alone, the linearly projected melting of the WAIS will add another 0.5 m of sea-level rise to the IPCC figure. A total of 1-m rise by 2100 is now considered a mainstream prediction in the community.

Worse still, Naish and his colleagues are now faced with clear evidence that the WAIS does not necessarily melt in a linear fashion, rather it is prone to highly unstable events that could lead to massive breakups, potentially adding up to 3.2 m of average sea-level rise in quite short periods of time. And, due to the way the earth’s gravitational field works, that average rise would not be distributed evenly over the earth’s surface; in some places like North America the rise could be up to 4.0 m… within our, or our children’s, lifetimes.

In the longer run, CO2 over 400 ppm commits the climate to a complete loss of the WAIS, the Greenland ice sheet and EAIS, totalling a sea-level rise of about 100 m. The evidence is now unassailable; a firm commitment to Copenhagen later this year is our last chance to act. Failure will bring only our grandchildren’s condemnation.

(And yes I took the train into town.)

Link to article: http://www.thestandard.org.nz/unassailable-evidence/

Written by fatih al-farahat in , , , , ,


Ted Scambos, Eric Steig, Tom Neumann, IPY, U.S.-Norwegian South Pole Traverse

ANTARCTICA NEWS ARCHIVES

Photo credit:Lou Albershardt

IPY Traverse


Posted: May 6, 2009

Courtesy: Antarctic Sun

by Peter Rejcek

The 12 scientists and support staff who made a slow crawl across a vast, blank stretch of East Antarctica this past austral summer for three months to study how regional climate variability relates to global climate change expected to encounter brutally cold storms and other challenges on the high polar plateau.

They didn’t expect to come across other travelers in the relatively unexplored area known as Queen Maud Land. But they did — three times in one day.

“We were astonished because we were supposed to be all alone,” said Ted Scambos , a member of the Norwegian-U.S. science team that crossed a large slice of the Antarctic continent using tracked vehicles pulling sleds. “I don’t know where you can go in order to be on the edge of the Earth anymore.”

The encounters, all involving people taking part in a commercial race to the South Pole, occurred near a fuel depot in an area where the ice sheet was more than 3,000 meters thick, hiding at least four distinct subglacial bodies of water called the Recovery Lakes.

“Fuel depots in Antarctica are kind of the equivalent of watering holes in Africa,” mused Scambos, lead scientist at the Boulder, Colo.-based National Snow and Ice Data Center. “Everybody has to come to the fuel depot, and you see all kinds of people, all kinds of groups, gathered at the fuel depot.”

But for most of the roundtrip journey between Norway’s Troll research station on the coast and the U.S. Antarctic Program’s South Pole Station , the scientists and crew were on their own. They took measurements of the snow and ice in areas that virtually no one had visited since the late 1960s, when the United States primarily used tractor trains to conduct deep-field science work.

Living and working out of bright red, boxed buildings mounted on sleds, the team collected ice cores at various depths and locations, used radar to map the ice sheet layers and dug snow pits — all in an effort to understand the climate in this area for the last thousand years and how it may be changing today. The project was part of the International Polar Year , a 60-nation effort to better understand the Antarctic and Arctic, which officially ended last month.

“It’s really been a blank spot on the map — on both the literal map as well as the metaphoric map of climate change in Antarctica,” said Tom Neumann , leader of the traverse team during the second leg of the two-year project that began in 2007-08 and covered nearly 7,000 kilometers including a few side trips. “[The traverse] should help fill in the picture of how Antarctica overall is changing.”

Scientists had believed that Antarctica was largely bucking the global warming trend. While West Antarctica was undoubtedly heating up — particularly the outstretched tip of the Antarctic Peninsula where ice shelves are disappearing at historic rates — studies of the much larger East Antarctic Ice Sheet suggested a cooling trend.

Some researchers have suggested the depletion of stratospheric ozone over Antarctica — the ozone hole that appears each austral spring — is affecting atmospheric circulation and westerly winds around the continent, effectively shielding it from global warming. But a paper in the journal Nature earlier this year said warming in West Antarctica is greater than whatever cooling may be occurring on the rest of the ice-covered continent.

“Simple explanations don’t capture the complexity of climate,” explained Eric Steig , lead author of the Nature paper and a professor at the University of Washington , in a statement back in January.

“The thing you hear all the time is that Antarctica is cooling, and that’s not the case,” added Steig, a collaborator on the IPY traverse project. “If anything it’s the reverse, but it’s more complex than that. Antarctica isn’t warming at the same rate everywhere, and while some areas have been cooling for a long time, the evidence shows the continent as a whole is getting warmer.”

Antarctica is roughly the size of the United States and Mexico: Snow in Denver doesn’t mean a blizzard stretches all the way down to Mexico City. “Antarctica is a huge place, and I would be surprised if it was all doing the same thing,” said Neumann, a scientist now with NASA Goddard Space Flight Center .

Yet there’s even a hint that East Antarctica — well, at least one spot on that incomplete map — may be warming based on one initial experiment by the traverse team. Scambos deployed strings of highly sensitive “thermometers” called thermistors into two of the deeper ice core holes.

The temperature on the ice sheet surface changes with the weather, but the temperature deeper down changes very slowly as the climate changes. Neumann likens it to throwing a frozen turkey into the oven — not the best way to cook a turkey, for sure, but eventually the center starts to thaw and cook based on the long-term outside temperature.

“It takes a while for the ice at 90 meters to notice how the surface temperature has changed,” Neumann explained. At that depth, the ice temperature is determined by the average temperature of the last 50 years or so. The instruments will operate for the next several years, allowing the scientists to determine how surface temperature changes through time.

“The initial results do say these areas are warming,” Neumann said, stressing that the measurements are in the hundredths of a degree per year and the data still raw.

Scambos: Recovery Lakes region was likely marine embayment in distant past
Most of the scientific analysis is yet to come. Neumann and others on the team will use the ice core samples to conduct stable isotopic measurements. By studying the isotopic ratios of oxygen 16 and oxygen 18, for instance, researchers can figure out what the climate was doing at a particular time because different ratios indicate different types of climate.

The chemistry will help the team calibrate the radar returns of the ice layers, a key step to nailing the snow accumulation rates in East Antarctica — one part of the equation to whether the ice sheet is overall losing or gaining mass. Loss of mass would indicate a rise in sea level.

“The chemistry from the core helps because it tells you the accumulation rate at a point,” Neumann explained. “For example, how deep is the fallout from the 1960s above-ground nuclear testing? That information helps to calibrate the radar layers that intersect the core site.

“If a radar layer is shallower, then it has had relatively less accumulation; a deep layer reflects relatively more accumulation. The information form the core lets you quantify the ‘relative’ statements above.”

The scientists also took the opportunity to explore the Recovery Lakes, an area of at least four lakes at the head of one of the largest ice streams draining East Antarctica. Ranging in size from 600 to 1,500 square kilometers, at depths well below sea level, the lakes were likely part of a deep marine embayment millions of years ago when the ice sheet was much smaller, according to Scambos.

“It was probably dynamic in the past,” he said. “In the distant future, if the Earth gets a great deal warmer, it would be dynamic again. I would prefer to think that we’ll stabilize climate change before we have to worry about this part of Antarctica disintegrating.”

There is still a lot of uncertainty about what the Antarctic ice sheets may do in the future because so little of it has been measured, particularly compared to Greenland, according to Neumann.

“The uncertainties in Greenland are getting quite a lot smaller as we get more and more data about ice velocity, ice thickness and accumulation rate. It’s certainly negative [mass balance] and we know roughly how negative it is in Greenland,” he said. “Antarctica is a bit of a different story, because it is so much larger and there’s places with so much less data, such as in East Antarctica.

“The physical insight is coming along and the model development is coming along, but I think it’s going to be a quite a while before we really have confidence in the large-scale predictive models of ice sheet change,” he added.

More ground-based studies like the traverse would help to continue filling in the blank spots of the climate change map, according to the scientists. “Most of that uncertainty [about Antarctica] can be beaten down with more and more measurements of accumulation rates,” Neumann said.

“The traverse system that the Norwegians have put together is fantastic, state-of-the-art. It’s the best in the world right now in terms of supporting a science crew over long distances,” Scambos said. “They essentially have a mobile, 12-person base that provides them relatively easy access to a large area. … [Queen Maud Land is] one of the least-explored areas of Antarctica, and I think that’s going to change, in part, thanks to this traverse system they’ve got.”

Link to this article:
http://antarcticsun.usap.gov/science/contenthandler.cfm?id=1758

Written by fatih al-farahat in , , , , ,


John Turner et al., By the end of the century we expect one third of Antarctic sea ice to disappear as ozone hole closes

BLOGGER'S NOTE: This is probably one of my most favorite subjects -- the vortices!

Why Antarctic ice is growing despite global warming

by Catherine Brahic, New Scientist, April 20, 2009

It's the southern ozone hole whatdunit. That's why Antarctic sea ice is growing while at the other pole, Arctic ice is shrinking at record rates. It seems CFCs and other ozone-depleting chemicals have given the South Pole respite from global warming.

Winds circle clockwise around Antarctica, whip off Victoria Land and create a vortex of cold storms (dark blue) off the Ross Sea, where sea ice is expanding. The vortex also draws in warm (red) air from South America, which warms the Antarctic Peninsula (Image: modified from Turner/AGU) -- Please click on the graphic to enlarge the details.

But only temporarily. According to John Turner of the British Antarctic Survey, the effect will last roughly another decade before Antarctic sea ice starts to decline as well.

Arctic sea ice is decreasing dramatically and reached a record low in 2007. But satellite images studied by Turner and his colleagues show that Antarctic sea ice is increasing in every month of the year except January. "By the end of the century we expect one third of Antarctic sea ice to disappear," says Turner. "So we're trying to understand why it's increasing now, at a time of global warming."

In a new study, Turner and colleagues show how the ozone hole has changed weather patterns around Antarctica. These changes have drawn in warm air over the Antarctic Peninsula in West Antarctica and cooled the air above East Antarctica.

The Southern Ocean is home to some of the strongest ocean winds on the planet. The region between 40° and 60° South is well-known to sailors who call it the "roaring forties" and "furious fifties."

Wind vortex

If the South Pole were smack in the middle of Antarctica, the winds would circle neatly around it in a clockwise direction. But in fact the continent is set slightly off-centre relative to the South Pole. As a result, the winds whip off Victoria Land and create a vortex over the Southern Ocean north of the Ross Sea (see blue area in figure). Turner compares this to the way wind going down a line of buildings will whip into a vortex when it comes to a corner.

The vortex generates a large area of storm activity. It also draws in warm air from South America over the Antarctic Peninsula, making this the warmest region of the continent.

By running an atmospheric computer model with and without the ozone hole, Turner and his colleagues found that the depletion of the ozone has intensified the winds of the roaring forties and furious fifties. The net result has been to draw more warm air in from Chile – which has warmed the Antarctic peninsula and caused the collapse of several ice shelves – and generate stronger cool-air storms around the Ross Sea.

Satellite data shows that sea ice has shrunk west of the Antarctic Peninsula and grown in the Ross Sea. Because the increase in sea ice extent has been greater than the reduction around the Antarctic peninsula, the net effect is that since the ozone hole appeared 30 years ago, Antarctic ice has grown. The researchers say their models suggest this is most likely a result of the ozone hole, although they cannot rule out the possibility that natural variations in sea ice extent have also played a role.

Ozone healing

"Over the next 50 to 100 years, the ozone hole will heal," says Turner. "At the same time, greenhouse gases will rise. In next decade or so we should see sea ice plateauing and then decreasing massively if greenhouse gases continue to increase."

Earlier this year, research led by Eric Steig of the University of Washington, Seattle, showed that although the Antarctic continent as a whole has warmed by 0.5 °C in the last 50 years – on a par with the global average – the figure hides strong regional differences. West Antarctica has warmed while temperatures over East Antarctica have dropped.

Accordingly, the disintegration of large ice shelves have all been in West Antarctica, the most famous example being the Larsen ice shelf. More recently, scientists have been anxiously expecting the Wilkins ice shelf to collapse as well.

Journal reference: Geophysical Research Letters (DOI: 10.1029/2009GL037524, in press).

Link to article: http://www.newscientist.com/article/dn16988-why-antarctic-ice-is-growing-despite-global-warming.html

Written by fatih al-farahat in , ,


Ted Scambos: East Antarctica is warming slightly


Environment ministers and other representatives from a dozen nations, on a fact-finding visit to Norway's Troll Research Station in Antarctica on Monday, Feb. 23, 2009, are shown here during a tour of the ice sheet below the Judulsessen massif of rock towers. Scientists reported in Geneva on Wednesday that, in a warming world, Antarctic glaciers are accelerating their dumping of ice into the sea, raising ocean levels. (AP Photo/Charles J. Hanley)

Ice in east Antarctica a bigger threat long term

by CHARLES J. HANLEY, AP, February 26, 2009

TROLL RESEARCH STATION, Antarctica (AP) — Antarctica's western ice sheet is pushing ever faster into the sea, but scientists know an even greater long-term threat lies here in the vast, little-explored whiteness of east Antarctica.

An "absolutely titanic" store of ice that sits atop the east Antarctic plateau should be more closely monitored by glaciologists, the world's thinly spread corps of ice specialists, says Ted Scambos, a leading U.S. expert whose team last weekend finished a two-month scientific expedition across the forbidding plateau.

Scambos and Tom Neumann, leader of that joint U.S.-Norwegian "traverse" from the South Pole to this Norwegian outpost, commented Wednesday after the release in Geneva of a report summarizing initial findings from the 2007–2009 International Polar Year (IPY), a program of intensified research in the polar regions.

That report said west Antarctica has been warming, ice shelves floating on the sea fringing the west coast are weakening, and the glaciers they hold back are pouring ice faster into the sea.

The report doesn't forecast immediate Antarctic disasters because of global warming. Scientists point out, however, that if the western ice sheet ever collapsed completely, it would add some 7 meters to sea levels worldwide.

East Antarctica's ice appears more stable than the west's — "I wouldn't say it's stable, but more stable," said Neumann — but it has the theoretical potential to add some 200 feet (60 meters) to sea levels in centuries to come, scientists say. Even a small, more immediate shift here could raise oceans significantly.

Concerned Norwegian researchers plan to investigate the state of the Fimbul Ice Shelf, a gigantic table of thick ice reaching 120 miles into the sea at the coast 100 miles north of this research station, which sits in a stony mountain valley hemmed in by glaciers rumbling in slow motion toward the far-off southern Atlantic.

Kim Holmen, research director for the Norwegian Polar Institute, which operates Troll, took note of the melting ice shelves of the west.

"This is something we think is happening to the ice shelves in Dronning Maud Land," he said, referring to this Norwegian-claimed sector of east Antarctica. "The water coming in under the shelves is 1 °C warmer" — almost 2 °F.

Scambos, lead scientist at the U.S. National Snow and Ice Data Center at the University of Colorado, pointed out that a recently published research paper in the journal Nature indicated that east Antarctica, contrary to earlier scientific belief, has been warming in recent decades.

"Our preliminary results support that," he said of the traverse expedition's research. "The temperature measurements we were able to make looks like there was a very slight warming."

The 12-member U.S.-Norwegian team drilled deep cores into the eastern ice sheet to assess recent and historical climate trends, checked ice thickness with radar, and made other measurements. They drove the 1,400 miles (2,300 km) in a caravan of snow tractors pulling research, kitchen and sleeping modules on giant skis.

The interior of east Antarctica is almost entirely unexplored. "The area we traveled through had not been visited by a scientific traverse since the 1960s," said NASA glaciologist Neumann.

"This part of Antarctica is approximately the same size as Greenland and we don't know very much about it," he said. "But I hope our data on the ground will allow us to make a much better assessment of how this area is changing."

That will take months of follow-up analysis. Meantime, Scambos said, Wednesday's IPY report "gives us an idea of what sort of trouble we are getting ourselves into if we don't begin to turn around the impact of greenhouse gases on climate."

Link to article: http://www.google.com/hostednews/ap/article/ALeqM5gCiXb1C_JnTZ19kwVF0k4Ld9b-FAD96J6H700

Written by fatih al-farahat in , , ,


From Earth Observatory -- more on the Antarctic Warming Trends

Antarctic Warming Trends

from NASA's Earth Observatory, January 23, 2009
Antarctic Warming Trends
Color bar for Antarctic Warming Trends
download large image (2 MB, JPEG) acquired 1957-2006

For a long time, it seemed that Antarctica was immune to global warming. Most of the icy southern continent, where temperatures can plummet to -80 °C (-112 °F), seemed to be holding steady or even cooling as the rest of the planet warmed. But a new analysis of satellite and weather station data has shown that Antarctica has warmed at a rate of about 0.12 °C (0.22 °F) per decade since 1957, for a total average temperature rise of 0.5 °C (1 °F).

This image, based on the analysis of weather station and satellite data, shows the continent-wide warming trend from 1957 through 2006. Dark red over West Antarctica reflects that the region warmed most per decade. Most of the rest of the continent is orange, indicating a smaller warming trend, or white, where no change was observed. The underlying land surface color is based on the Landsat Image Mosaic of Antarctica (LIMA) data set, while the topography is from a Radarsat-based digital elevation model. Sea ice extent in the Southern Ocean surrounding the continent is based on data from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) collected on May 14, 2008 (late fall in the Southern Hemisphere).

The image paints a different picture of temperature trends in Antarctica than scientists had previously observed. Limited weather station measurements had recorded a dramatic warming trend along the peninsula, which juts into warmer waters in the Southern Ocean, but the few stations that dotted the rest of the continent reported that temperatures there had not changed or had cooled. It has been difficult to get a clear picture of temperature trends throughout Antarctica because measurements are so scarce. Few weather stations exist, and most of these are near the coast where they are relatively accessible. These coastal locations left vast regions of the continent’s interior where the temperature has never been monitored routinely. Satellites can measure the ground temperature of the entire continent, but only on clear days, when clouds don't obscure the view. Since satellite measurements are always taken in the same sort of weather conditions, they can be skewed.

Eric J. Steig (University of Washington), David P. Schneider (National Center for Atmospheric Research), Scott D. Rutherford (Roger Williams University), Michael E. Mann (Pennsylvania State University), Josefino C. Comiso (NASA Goddard Space Flight Center), and Drew T. Shindell (NASA Goddard Institute for Space Studies and Columbia University) collaborated to combine the day-to-day accuracy of weather stations with the continental coverage of satellite measurements. Led by Steig, the team compared 26 years of temperature measurements from the Advanced Very High Resolution Radiometer (AVHRR), a satellite sensor run by the National Oceanic and Atmospheric Association, with simultaneous weather station measurements.

This allowed the group to map out the relationship between ground measurements and satellite measurements so that they knew roughly what the satellite temperature would be when the thermometer at a weather station registered -5 °C, for example. The team used this relationship to extrapolate what the satellite would have recorded over the whole continent had it been in orbit when the weather station record began in 1957. Once the group reached the period when the satellite was in orbit, they checked the extrapolated values against the actual measurements to confirm that the method was sound. In the end, they generated a 50-year record of temperatures across Antarctica. Their work was published in the January 22, 2009, issue of Nature.

  1. References

  2. Hansen, K. (2009, January 22). Satellites confirm half-century of West Antarctic warming. NASA. Accessed January 22, 2009.
  3. Steig, E., Schneider, D., Rutherford, S., Mann, M., Comiso, J., and Shindell, D. (2009, January 22). Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year. Nature, 457, 459-463. doi:10.1038/nature07669.
  4. Steig, E. (2009, January 21). State of Antarctica: red or blue? RealClimate. Accessed January 22, 2009.

Image courtesy Trent Schindler, NASA Goddard Space Flight Center Scientific Visualization Studio. Caption by Holli Riebeek.

Instrument:
NOAA-15 POES - AVHRR
Link to article: http://earthobservatory.nasa.gov/IOTD/view.php?id=36736

Written by fatih al-farahat in , ,


NASA GISS reports on Antarctic warming research by Eric Steig et al., Nature

Antarctic warming

This illustration depicts the warming that scientists have determined has occurred in West Antarctica during the last 50 years, with the dark red showing the area that has warmed the most.
Color bar for Antarctic Warming Trends

Red represents areas where temperatures have increased the most during the last 50 years, particularly in West Antarctica, while dark blue represents areas with a lesser degree of warming. Temperature changes are measured in degrees Celsius. Credit: Image courtesy Trent Schindler, NASA Goddard Space Flight Center Scientific Visualization Studio. Caption by Holli Riebeek.

Satellites Confirm Half-Century of West Antarctic Warming

[Blogger's note: Hank Roberts took the time and trouble to find two very useful links to information in the Nature article, which he posted in a comment on the RealClimate blog post -- thank you, Hank!]

See Figure 2 of the published article published in Nature with graphs of temperature trends for East and West Antarctica here:

http://lawprofessors.typepad.com/environmental_law/2009/01/antarctic-warmi.html

Link to the published article's supplementary information full of graphs and explanations:

http://www.nature.com/nature/journal/v457/n7228/extref/nature07669-s1.pdf


Jan. 21, 2009

The Antarctic Peninsula juts into the Southern Ocean, reaching farther north than any other part of the continent. The southernmost reach of global warming was believed to be limited to this narrow strip of land, while the rest of the continent was presumed to be cooling or stable.

Not so, according to a new analysis involving NASA data. In fact, the study has confirmed a trend suspected by some climate scientists.

"Everyone knows it has been warming on the Antarctic Peninsula, where there are lots of weather stations collecting data," said Eric Steig, a climate researcher at the University of Washington in Seattle, and lead author of the study. "Our analysis told us that it is also warming in West Antarctica."

The finding is the result of a novel combination of historical temperature data from ground-based weather stations and more recent data from satellites. Steig and colleagues used data from each record to fill in gaps in the other and to reconstruct a 50-year history of surface temperatures across Antarctica.

Over the years, climate research in northern latitudes led researchers to believe that the Arctic is where impacts of global climate change would be seen first. Less certain is how climate is affecting Antarctica where inland temperatures are known to plunge to -112°F, and ground-based weather stations have been sparse.

It's this sparse data collection — from ground-stations on the Antarctic Peninsula and previous reports that much of East Antarctica has experienced cooling since 1978 — that led the International Panel on Climate Change to conclude in its most recent report that Antarctica is the one continent where we have failed to detect human-caused temperature changes.

With funding from the National Science Foundation's Office of Polar Programs, Steig and colleagues set out to reconstruct Antarctica's recent past. Ground-based stations have recorded temperatures since 1957, but most of those readings come from the peninsula and areas on the edges of the continent. But at the same time, scientists such as study co-author Joey Comiso of NASA's Goddard Space Flight Center in Greenbelt, Md., have been gathering measurements from a series of Advanced Very High Resolution Radiometer (AVHRR) instruments deployed on satellites since 1981.

To construct the new 50-year temperature record, the team applied a statistical technique to estimate temperatures missing from ground-based observations. They calculated the relationship between overlapping satellite and ground-station measurements over the past 26 years. Next, they applied that correlation to ground measurements from 1957 to 1981 and calculated what the satellites would have observed.

The new analysis shows that Antarctic surface temperatures increased an average of 0.22°F (0.12°C) per decade between 1957 and 2006. That's a rise of more than 1°F (0.5°C) in the last half century. West Antarctica warmed at a higher rate, rising 0.31°F (0.17°C) per decade. The results, published Jan. 22 in Nature, confirm earlier findings based on limited weather station data and ice cores.

While some areas of East Antarctica have been cooling in recent decades, the longer 50-year trend depicts that, on average, temperatures are rising across the continent.

The northern section of the Larsen B ice shelf, a large floating ice mass on the eastern side of the Antarctic Peninsula, shattered and separated from the continent on March 5, 2002, and represents a major impact that climate warming can have on the region. Credit: NASA Earth Observatory.

West Antarctica is particularly vulnerable to climate changes because its ice sheet is grounded below sea level and surrounded by floating ice shelves. If the West Antarctic ice sheet completely melted, global sea level would rise by 16-20 feet (5-6 meters).

To identify causes of the warming, the team turned to Drew Shindell of NASA's Goddard Institute for Space Studies in New York, who has used computer models to identify mechanisms driving Antarctica's enigmatic temperature trends.

Previously, researchers focused on Antarctic ozone depletion, which influences large-scale atmospheric fluctuations around the continent — most notably, the Southern Annular Mode, which speeds up wind flow to isolate and cool the continent.

Shindell compared Steig's temperature data with results from a computer model that can simulate the response of the atmospheric system to changes in land surface, ice cover, sea surface temperatures, and atmospheric composition. He found the ozone-influenced Southern Annular Mode is not necessarily the primary influence on Antarctic climate. Instead, it appears that smaller-scale, regional changes in wind circulation are bringing warmer air and more moisture-laden storms to West Antarctica.

"We still believe ozone depletion can increase wind speeds around Antarctica, further isolating the interior," Shindell said. "But it's clear now that it's not such a dominant influence on temperature trends."

Reference

Steig, E.J., D.P. Schneider, S.D. Rutherford, M.E. Mann, J.C. Comiso, and D.T. Shindell, 2009: Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year. Nature, 457, 459-462, doi:10.1038/nature07669.

Media Contacts

Kathryn Hansen, 301-286-8955, NASA Goddard Space Flight Center, Greenbelt, Md.

Leslie McCarthy, 212-678-5507, NASA Goddard Institute for Space Studies, New York, N.Y.

This article is derived from a NASA "Looking at Earth" feature.

Link to this page at NASA GISS: http://www.giss.nasa.gov/research/news/20090121/

Written by fatih al-farahat in , , , , , ,


Latest research on Antarctic warming explained by Eric Steig on RealClimate

State of Antarctica: red or blue?

RealClimate, 21 January 2009

— eric @ 1:10 PM

A couple of us (Eric and Mike) are co-authors on a paper coming out in Nature this week (Jan. 22, 09). We have already seen misleading interpretations of our results in the popular press and the blogosphere, and so we thought we would nip such speculation in the bud.

The paper shows that Antarctica has been warming for the last 50 years, and that it has been warming especially in West Antarctica (see the figure). The results are based on a statistical blending of satellite data and temperature data from weather stations. The results don't depend on the statistics alone. They are backed up by independent data from automatic weather stations, as shown in our paper as well as in updated work by Bromwich, Monaghan and others (see their AGU abstract, here), whose earlier work in JGR was taken as contradicting ours. There is also a paper in press in Climate Dynamics (Goosse et al.) that uses a GCM with data assimilation (and without the satellite data we use) and gets the same result. Furthermore, speculation that our results somehow simply reflect changes in the near-surface inversion is ruled out by completely independent results showing that significant warming in West Antarctica extends well into the troposphere. And finally, our results have already been validated by borehole thermometery — a completely independent method — at at least one site in West Antarctica (Barrett et al. report the same rate of warming as we do, but going back to 1930 rather than 1957; see the paper in press in GRL).

Here are some important things the paper does NOT show:

1) Our results do not contradict earlier studies suggesting that some regions of Antarctica have cooled. Why? Because those studies were based on shorter records (20-30 years, not 50 years) and because the cooling is limited to the East Antarctic. Our results show this too, as is readily apparent by comparing our results for the full 50 years (1957-2006) with those for 1969-2000 (the dates used in various previous studies), below.

2) Our results do not necessarily contradict the generally-accepted interpretation of recent East Antarctic cooling put forth by David Thompson (Colorado State) and Susan Solomon (NOAA Aeronomy Lab). In an important paper in Science, they presented evidence that this cooling trend is linked to an increasing trend in the strength of the circumpolar westerlies, and that this can be traced to changes in the stratosphere, mostly due to photochemical ozone losses. Substantial ozone losses did not occur until the late 1970s, and it is only after this period that significant cooling begins in East Antarctica.

3) Our paper — by itself — does not address whether Antarctica's recent warming is part of a longer term trend. There is separate evidence from ice cores that Antarctica has been warming for most of the 20th century, but this is complicated by the strong influence of El Niño events in West Antarctica. In our own published work to date (Schneider and Steig, PNAS), we find that the 1940s [edit for clarity: the 1935-1945 decade] were the warmest decade of the 20th century in West Antarctica, due to an exceptionally large warming of the tropical Pacific at that time.

So what do our results show? Essentially, that the big picture of Antarctic climate change in the latter part of the 20th century has been largely overlooked. It is well known that it has been warming on the Antarctic Peninsula, probably for the last 100 years (measurements begin at the sub-Antarctic Island of Orcadas in 1901 and show a nearly monotonic warming trend). And yes, East Antarctica cooled over the 1980s and 1990s (though not, in our results, at a statistically significant rate). But West Antarctica, which no one really has paid much attention to (as far as temperature changes are concerned), has been warming rapidly for at least the last 50 years.

Why West Antarctica is warming is just beginning to be explored, but in our paper we argue that it basically has to do enhanced meridional flow — there is more warm air reaching West Antarctica from farther north (that is, from warmer, lower latitudes). In the parlance of statistical climatology, the "zonal wave 3 pattern" has increased (see Raphael, GRL 2004). Something that goes along with this change in atmospheric circulation is reduced sea ice in the region (while sea ice in Antarctica has been increasing on average, there have been significant declines off the West Antarctic coast for the last 25 years, and probably longer). And in fact this is self reinforcing (less sea ice, warmer water, rising air, lower pressure, enhanced storminess).

The obvious question, of course, is whether those changes in circulation are themselves simply "natural variability" or whether they are forced — that is, resulting from changes in greenhouse gases. There will no doubt be a flurry of papers that follow ours, to address that very question. A recent paper in Nature Geosciences by Gillet et al. examined trends in temperatures in the both Antarctic and the Arctic, and concluded that "temperature changes in both … regions can be attributed to human activity." Unfortunately our results weren't available in time to be made use of in that paper. But we suspect it will be straightforward to do an update of that work that does incorporate our results, and we look forward to seeing that happen.

Postscript
Some comment is warranted on whether our results have bearing on the various model projections of future climate change. As we discuss in the paper, fully-coupled ocean-atmosphere models don't tend to agree with one another very well in the Antarctic. They all show an overall warming trend, but they differ significantly in the spatial structure. As nicely summarized in a paper by Connolley and Bracegirdle in GRL, the models also vary greatly in their sea ice distributions, and this is clearly related to the temperature distributions. These differences aren't necessarily because there is anything wrong with the model physics (though schemes for handling sea ice do vary quite a bit model to model, and certainly are better in some models than in others), but rather because small differences in the wind fields between models results in quite large differences in the sea ice and air temperature patterns. That means that a sensible projection of future Antarctic temperature change — at anything smaller than the continental scale — can only be based on looking at the mean and variation of ensemble runs, and/or the averages of many models. As it happens, the average of the 19 models in AR4 is similar to our results — showing significant warming in West Antarctica over the last several decades (see Connolley & Bracegirdle's Figure 1).

A comment and response:

  1. Steve D. Says:
    22 January 2009 at 4:32 AM

    On many occasions on this site it’s been said that cooling in Antartica is consistent with AGW, as the models show etc…. Now it appears that a warming Antarctica is also consistent with AGW. I am curious to know, is there any kind of change in temperature down there which would invalidate the AGW thesis?

    [Response:Why do the critics think that everything is so simple and binary, for example that we can lump all anthropogenic forcings into a simple “AGW” forcing. Guess what, its not that simple. There are multiple anthropogenic forcings that have quite different impacts (e.g. anthropogenic greenhouse gas increases, aerosols, land-use changes and, yes, stratospheric ozone depletion). Anyone who follows the science is of course aware of this. The temperature trends in Antarctica depend on the time interval and season one looks at, because certain forcings, such as ozone depletion, are particularly important over restricted past time intervals and during particular seasons. The interval over which we expect cooling of the interior is when ozone depletion was accelerating (1960s through late 20th century) and this is precisely when we reproduce the cooling trend both in the reconstruction (primarily during the Austral fall season) and the model simulation experiments discussed in the paper. Over the longer-term, and in the annual mean, greenhouse warming wins out over the more temporary and seasonally-specific impacts of ozone depletion in our simulations, and apparently in the real world. Do you really think that all of the authors and reviewers would have overlooked a basic internal contradiction of logic of the sort you imply, if it actually existed? This is all discussed in detail in the paper. Why not go to your local library and read it and perhaps learn something? -mike]


Link to RealClimate blog post: http://www.realclimate.org/index.php/archives/2009/01/state-of-antarctica-red-or-blue/