Climate & Climate Change

A new paper has been published which examines the factors involved in the 2002 collapse of the Larsen B ice shelf in Antarctica.

The lead author, Professor Neil Glasser of Aberystwyth University (Wales, UK) was interviewed about the findings in the Western Mail on 7th February:

‘Antarctic ice shelf did not just melt away’

Excerpt: Prof Glasser told the Western Mail, “Climate change may have been the last straw, but it was not the only straw.”

“Ice shelf collapse is not as simple as we first thought,” said Prof Glasser, lead author of the paper.”

“Because large amounts of meltwater appeared on the ice shelf just before it collapsed, we had always assumed that air temperature increases were to blame.”

“But our new study shows that ice-shelf break-up is not controlled simply by climate. A number of other atmospheric, oceanic and glaciological factors are involved.”

“The location and spacing of fractures on the ice shelf such as crevasses and rifts are very important too, because they determine how strong or weak the ice shelf is.”

Prof Glasser pointed out that he is not a climate change sceptic.

The full paper entitled, ‘A structural glaciological analysis of the 2002 Larsen B ice shelf collapse’ is currently available for free download from the Journal of Glaciology.

The Abstract reads:

This study provides a detailed structural glaciological analysis of changes in surface structures on the Larsen B ice shelf on the Antarctic Peninsula prior to its collapse in February–March 2002. Mapped features include the ice-shelf front, rifts, crevasses, longitudinal linear surface structures and meltwater features. We define domains on the ice shelf related to glacier source areas and demonstrate that, prior to collapse, the central Larsen B ice shelf consisted of four sutured flow units fed by Crane, Jorum, Punchbowl and Hektoria/Green/Evans glaciers. Between these flow units were ‘suture zones’ of thinner ice where the feeder glaciers merged. Prior to collapse, large open-rift systems were present offshore of Foyn Point and Cape Disappointment. These rifts became more pronounced in the years preceding break-up, and ice blocks in the rifts rotated because of the strong lateral shear in this zone. Velocity mapping of the suture zones indicates that the major rifts were not present more than about 20 years ago. We suggest that the ice shelf was preconditioned to collapse by partial rupturing of the sutures between flow units. This, we believe, was the result of ice-shelf front retreat during 1998–2000, reducing the lateral resistive stress on the upstream parts of the shelf and glacier flow units, ice-shelf thinning and pre-shelf-break-up glacier acceleration.

While we are on the subject of the Larsen B (and A) ice shelf, I am reminded of a paper from 2006, published in QUATERNARY SCIENCE REVIEWS, entitled: ‘Ice shelf history from petrographic and foraminiferal evidence, Northeast Antarctic Peninsula’

This paper suggests that there was “widespread ice shelf breakup in the mid-Holocene.” This finding is harmonious with the earlier finding of Pudsey and Evans (2001) that the adjacent Prince Gustav Channel ice shelf also retreated in mid-Holocene time, but that subsequent colder conditions, in their words, “allowed the ice shelf to reform.” It is also in harmony with the finding of Vaughan et al. (2001) that from 6000 to 1900 years ago the Prince Gustav Channel ice shelf, as they describe it, “was absent and climate was as warm as it has been recently.” Consequently, and most recently, Pudsey et al. concluded that “the maximum ice shelf limit may date only from the Little Ice Age,” which they report is “widely recognized” to have held sway in that part of the world between 700 and 150 years ago.

A large body of data makes it pretty clear that the greatest extent of the Larsen ice shelf during the current interglacial likely occurred only a few hundred years ago, and that the portions of it that recently disintegrated (Larsen-A and Larsen-B) were probably created about that same time. In addition, it would appear that some 2000 years ago the Larsen-A and B ice shelves likely were altogether absent, and that temperatures of that time were likely as warm as, or even warmer than, they have been recently. Furthermore, there was approximately 100 ppm less CO2 in the air of that time than there is in the air of today; and this fact suggests that something other than anthropogenic CO2 emissions was the cause of the earlier “balmy” conditions of northeast Antarctica, which implies that that same something else, or something different yet, could well be responsible for the current warmth of the region.
(CO2Science.org, December 2006)

The Abstract reads:

A detailed record of late Pleistocene deglaciation followed by mid-Holocene ice shelf breakup and late Holocene re-growth is contained in continental shelf sediments in the northern Larsen area, northeast Antarctic Peninsula. The zero age of core tops is confirmed by new and published 210Pb profiles, and 70 accelerator mass spectrometer (AMS) 14C dates on bulk organic carbon define sedimentation rates of 7.6–92 cm/ka. The varied geology in the local ice drainage basins facilitates the use of ice-rafted debris (IRD) provenance in determining the presence or absence of ice shelves. All inshore cores contain an interval of non-local IRD in the post-glacial section, demonstrating widespread ice shelf breakup in the mid-Holocene. Both breakup and re-growth may have taken centuries and there are no widespread debris layers associated with breakup. Cores beyond and up to 30 km inside the historical ice shelf limit exhibit a varied IRD provenance throughout the Holocene, suggesting the maximum ice shelf limit may date only from the Little Ice Age. Benthic foraminiferal assemblages are related to water masses and position on the continental shelf and have been modified by taphonomic processes. Nevertheless we discern a deglaciation signal in Prince Gustav Channel of a calcareous spike in predominantly agglutinated assemblages, and this is repeated at the time of mid-Holocene ice shelf breakup. The inferred mid-Holocene warm period occurred later in the northern Larsen area than on the west coast of the Antarctic Peninsula.

The above papers suggest that the collapse of the Larsen B ice shelf in 2002 wasn’t simple or unprecedented.

A new paper published in Climate Dynamics claims a temperature trend of -0.3°C over the last 1,500 years in an Arctic location. The paper by Håkan Grudd is entitled: ‘Torneträsk tree-ring width and density ad 500–2004: a test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers’

The Abstract states:

This paper presents updated tree-ring width (TRW) and maximum density (MXD) from Torneträsk in northern Sweden, now covering the period ad 500–2004. By including data from relatively young trees for the most recent period, a previously noted decline in recent MXD is eliminated. Non-climatological growth trends in the data are removed using Regional Curve Standardization (RCS), thus producing TRW and MXD chronologies with preserved low-frequency variability. The chronologies are calibrated using local and regional instrumental climate records. A bootstrapped response function analysis using regional climate data shows that tree growth is forced by April–August temperatures and that the regression weights for MXD are much stronger than for TRW. The robustness of the reconstruction equation is verified by independent temperature data and shows that 63–64% of the instrumental inter-annual variation is captured by the tree-ring data. This is a significant improvement compared to previously published reconstructions based on tree-ring data from Torneträsk. A divergence phenomenon around ad 1800, expressed as an increase in TRW that is not paralleled by temperature and MXD, is most likely an effect of major changes in the density of the pine population at this northern tree-line site. The bias introduced by this TRW phenomenon is assessed by producing a summer temperature reconstruction based on MXD exclusively. The new data show generally higher temperature estimates than previous reconstructions based on Torneträsk tree-ring data. The late-twentieth century, however, is not exceptionally warm in the new record: On decadal-to-centennial timescales, periods around ad 750, 1000, 1400, and 1750 were equally warm, or warmer. The 200-year long warm period centered on ad 1000 was significantly warmer than the late-twentieth century (p < 0.05) and is supported by other local and regional paleoclimate data. The new tree-ring evidence from Torneträsk suggests that this “Medieval Warm Period” in northern Fennoscandia was much warmer than previously recognized. The paper concludes: The Tornetra¨sk records of MXD and TRW are updated to AD 2004. By including MXD data from relatively young trees in the most recent period, a previously noted apparent loss of sensitivity to temperature is eliminated. These new data enable a much improved reconstruction of summer temperature for the last 1,500 years in northern Fennoscandia. Previous climate reconstructions based on tree-ring data from Tornetra¨sk were biased by a divergence phenomenon in TRW around AD 1800 and therefore show erroneously low temperature estimates in the earlier part of the records. Tornetra¨sk MXD does not show this ‘‘divergence problem’’ and hence produces robust estimates of summer temperature variation on annual to multi-century timescales. The late-twentieth century is not exceptionally warm in the new Tornetra¨sk record: On decadal-to-century timescales, periods around AD 750, 1000, 1400, and 1750 were all equally warm, or warmer. The warmest summers in this new reconstruction occur in a 200-year period centred on AD 1000. A ‘‘Medieval Warm Period’’ is supported by other paleoclimate evidence from northern Fennoscandia, although the new tree-ring evidence from Tornetra¨sk suggests that this period was much warmer than previously recognised. The paper is available under 'Open Access.' See also World Climate Report: ‘1500 Years of Cooling in the Arctic’

I have previously blogged about the record low (since satellite measurements began) for Arctic sea ice in 2007, and some of the contributory factors, here, here and here. The record high for sea ice coverage in the Antarctic received little or no media attention.

So what is the current situation? NASA’s earth observatory has an Arctic sea ice update here:

“After record retreat in September 2007, Arctic sea ice had been making a slow winter recovery. Mean sea ice extent remained at record-low levels in October 2007, but beginning in late October, sea ice grew by more than 150,000 square kilometers (about 58,000 square miles) per day for about 10 days—the fastest regrowth observed in the satellite record. Despite this rapid growth, sea ice extent remained below normal for November, though it was not a record low.”

According to the University of Illinois website The Cryosphere Today, sea ice coverage for January 31 2008 is about 900,000 square kilometers below average for the Arctic and about 500,000 square kilometers above average for the Antarctic. Compare past Arctic sea ice coverage from 1980 onwards with the present at the same time of the year here.

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Roger Pielke, Jr. is a believer in man-made global warming. Pielke Jr. directs the University of Colorado’s Center for Science and Technology Policy Research and also is an associate professor of environmental studies. So the article below is a very significant slam against Andrew Dessler, Eli Rabett and Raymond Pierrehumbert.

Pielke JR (not SR) Takes on Critics of Senate 400 ‘Consensus Busters’ Scientist Report!

Pielke Jr. Slams ‘Attack Dog climate scientists’ engaging in ‘Character Assassination’ of Scientists on Senate Report

Excerpt: And this leads to the repugnant behavior of the attack dog climate scientists who otherwise would like to be taken seriously. By engaging in the character assassination of people who happen to find themselves on Senator Inhofe’s list they reinforce the absurd notion that scientific claims can be adjudicated solely by head counts and a narrow view of professional qualifications. They can’t. (See this enlightening and amusing discussion by Dan Sarewitz of leading experts arguing over who is qualified to comment on climate issues.) But by suggesting that knowledge claims can be judged by credentials the attack dog scientists reinforce an anti-democratic authoritarian streak found in the activist wing of the climate science community. Of course, from the perspective of the activist scientists such attacks may be effective if they dissuade other challenges to orthodoxy, but surely climate scientists deserving of the designation should be encouraging challenges to knowledge claims, rather than excoriating anyone who dares to challenge their beliefs. […]The climate science community – or at least its most publicly visible activist wing – seems to be working as hard as possible to undercut the legitimacy and the precarious trust than society provides in support of activities of the broader scientific community. Senator Inhofe is a politician, and plays politics. If activist climate scientists wish to play the Senator’s game, then don’t be surprised to see common wisdom viewing these activists more as political players than trustworthy experts. If this is correct then maybe the Senator is a bit more astute than given credit for.

http://sciencepolicy.colorado.edu/prometheus/archives/science_politics/001338witanagemot_justice_.html

A new paper published in the journal Geology suggests that it may be possible to seed carbon-rich environments with bacteria to create natural gas reservoirs. The study may also help explain high levels of methane in the atmosphere that occurred between ice ages, a trend recorded in ice cores taken from Greenland and Antarctica.

Read more in ScienceDaily: ‘Natural Gas Formation By Bacteria Linked To Climate Change And Renewable Energy’

The original paper is here:

Geology
Article: pp. 139–142 Volume 36, Issue 2 (February 2008)

Abstract

A new model linking atmospheric methane sources to Pleistocene glaciation via methanogenesis in sedimentary basins

M.J. Formolo1, J.M. Salacup1, S.T. Petsch1, A.M. Martini2, and K. Nüsslein3

1. Department of Geosciences, University of Massachusetts–Amherst, Amherst, Massachusetts 01003, USA, 2. Department of Geology, Amherst College, Amherst, Massachusetts 01002, USA, 3. Department of Microbiology, University of Massachusetts–Amherst, Amherst, Massachusetts 01003, USA

Methane (CH4) is an important greenhouse gas and amplifier of climate change. However, the causes of atmospheric CH4 variations over glacial-interglacial cycles remain unresolved. We propose that microbial methanogenesis along the shallow margins of sedimentary basins provides a source of atmospheric CH4 temporally connected with both advance and retreat of continental ice sheets. Extensive biodegradation of hydrocarbons in the Antrim Shale Formation, Michigan, United States, is associated with an active subsurface consortium of fermentative and methanogenic microorganisms. This activity was initially stimulated when saline formation waters were diluted by meltwater derived from overriding Pleistocene ice sheets. During glaciation, CH4 produced by this community accumulated in the shale at a rate of 1 Tg CH4 per 1000 yr as a result of ice coverage and increased hydrostatic pressure. We estimate that at present the Antrim Shale contains only 12%–25% of the cumulative mass of CH4 generated in the shale over the Pleistocene, indicating that CH4 that had accumulated during glaciation was subsequently released following ice-sheet retreat. While release from the Antrim Shale represents only a small part of the global CH4 budget, when extended to other glaciated sedimentary basins, subsurface methanogenesis may generate a substantial, previously unrecognized source of atmospheric CH4 during deglaciation.

Keywords: methane, biogeochemistry, black shale, glaciation

The UK’s CRU has updated its HadCRUT3v temperatures. Global average anomalies for November and December 2007 are now present but are provisional for a few months in case late data arrives.

No wonder newspaper reports haven’t mentioned it – November’s global temperature anomaly of 0.258 was the lowest since October 2000’s 0.201 and December 2007 was 0.221. The annual global average anomaly for 2007 is currently shown as 0.398, or the coolest since year 2000.

The annual average for the Southern Hemisphere in 2007 was the lowest since 1996. November and December temperatures were the coolest since 1992.

The annual average for the Northern Hemisphere remained at the 2002-2006 level. A very warm start to the year offset the cooling late in the year.

Global data at http://www.cru.uea.ac.uk/cru/data/temperature/hadcrut3vgl.txt.

Other data available via
http://www.cru.uea.ac.uk/cru/data/temperature/

(under “HadCRUT3v” in table about 50% down the page).

John McLean