RealClimate logo


Technical Note: Sorry for the recent unanticipated down-time, we had to perform some necessary updates. Please let us know if you have any problems.

Ice Shelf Instability

Filed under: — group @ 12 June 2008

Guest contribution from Mauri S. Pelto

Ice shelves are floating platforms of ice fed by mountain glaciers and ice sheets flowing from the land onto the ocean. The ice flows from the grounding line where it becomes floating to the seaward front, where icebergs calve. For a typical glacier when the climate warms the glacier merely retreats, reducing its low elevation, high melting area by increasing its mean elevation. An ice shelf is nearly flat and cannot retreat in this fashion. Ice shelves cannot persist unless the entire ice shelf is an accumulation zone, where snowpack does not completely melt even in the summer.



Ice shelves have long been recognized as keys in buttressing Antarctic Ice Sheets. In turn ice shelves rely on pinning points for buttressing. The pinning point are where the floating ice shelf meets solid ground, either at lateral margins or a subglacial rise meets the bottom of the ice shelf causing an ice rise on the shelf surface.

The recent collapse of Wordie Ice Shelf, Mueller Ice Shelf, Jones Ice Shelf, Larsen-A and Larsen-B Ice Shelf on the Antarctic Peninsula has made us aware of how dynamic ice shelve systems are. After their loss the reduced buttressing of feeder glaciers has allowed the expected speed-up of inland ice masses after shelf ice break-up. (Rignot and others, 2004).

Several recent papers examine the causes of breakup of both Larsen B and Wilkins Ice Shelf, which prompts a closer look at the role of surface melting, structural weakness development and ice shelf thinning in this process.

In 1995 a substantial section of the northern Larsen Ice Shelf broke up in a few days. This was the first glimpse at a rapid ice shelf collapse. The breakup followed a period of warming and ice shelf front retreat, prompting (Rott and others, 1996) to observe that “after an ice shelf retreats beyond a critical limit, it may collapse rapidly as a result of perturbated mass balance”.

During the austral summer of 2001/02, melting at the surface of Larsen Ice Shelf in the Antarctic Peninsula was three times in excess of the mean. This exceptional melt event was followed by the collapse of Larsen B Ice Shelf, during which 3,200 km2 of ice shelf surface was lost. That meltwater was playing a key role in collapse was underscored by the unusual number of melt ponds that existed that summer and that the new ice front after collapse close to the limit of surface meltponds seen in images leading up to the March event (Scambos and others, 2003).

The ice shelves actually collapse via rapid calving, and the physics connecting meltwater to calving is its ability to enhance crevasse propagation. When filled 90% or more with meltwater a sufficiently deep crevasse can overcome the overburden pressure that tends to close the crevasse at depth (Scambos and others, 2000). Days before the final Larsen break-up, it is evident that the crevasses cut through the entire ice shelf. It also appeared that large meltponds contracted indicating that they were beginning to drain though the crevasses to the sea (Scambos and others, 2003).

As scientists it would have been easy to close the book on the issue after identifying the meltwater process. However, detailed examinations have continued identifying other key elements in the tale of collapse. The decade prior to collapse the Larsen-B Ice Shelf had thinned primarily by melting of the ice shelf bottom by 18 m (Shepard and others, 2003). This preconditions the ice shelf to failure by weakening its connection to pinning points as the shelf becomes more buoyant. This goes back to the critical limit mentioned by Rott (1996).

Glasser and Scambos (2008) reexamined the Larsen Ice Shelf breakup for structural weaknesses and observed the following. They noted that the rifting and crevasses parallel to the ice front crosscut the meltwater channels and ponds, hence, post dating them. The number and length of the rifts increased markedly in the year before collapse. Substantial rifts also existed between tributary glaciers feeding the ice shelf as far as 40 km behind the ice front. Enlargement of and development of new rifts in these regions occurred in the year prior to collapse. Downstream of the tributary glacier junction there are no evidence of relict rifts, illustrating that these rifts are a feature of the last 20 years. After ice shelf collapse the ice front receded to the pre-existing rifts, and the pre-existing rifts defined the area of collapse. In this case the structural weaknesses preconditioned the ice to rapid breakup. Rift formation occurred in areas of velocity differences and natural weaknesses Velocity differences are largest between tributaries and near the ice front.

The latest example of a collapsing ice shelf is Wilkins Ice Shelf (WIS), which lost 425 km2 in late February and early March 2008. The dynamic nature of the WIS is examined by Braun, Humbert and Moll (2008), their findings are summarized below. WIS is buttressed by Alexander, Latady, Charcot and Rothschild Island and by numerous small ice rises, indicating subglacial contact. Recent history indicates that WIS experiences no continuous ordinary calving, but single break-up events of various magnitudes. They further show that drainage of melt ponds into crevasses were of no relevance for the break-up at WIS. On WIS the evolution of failure zones is associated with ice rises. Analysis of rifting indicated that in 1990 the central area of WIS did not have any substantial rifts. In 1993/94, rift formation started to expand at the northern ice front. Today, the central part of WIS is intersected by long rifts that formed in and around ice rises. The rifts can cover tens of kilometers. The evolution and coalescing of the rifts are followed by break-up events at the ice front. Hence, the connection of rift systems seems to be the trigger for collapse. The recent break-up has left a narrow 6 km wide; already fractured connection to Charcot Island in a sensitive area that is stabilizing the northern part of the ice shelf. A new rift connection formed between already existing fractures, crosses almost the entire northern shelf, which makes WIS even more fragile and vulnerable. This area of interconnected rifts is 2100 km2. An additional 3000 km2 of the 13 000km2 of WIS, is at risk if this connection to Charcot Island is lost as rifts around the Petrie Ice Rise indicate an area of weakness. The conclusion for WIS is pre-conditioning of the ice shelf by failure zones occurring at ice rises and triggered by break-up events are leading to a sequence cascade of failure.

Below you can see the evident rifts near Charcot Island in this March MODIS image and the narrow connection of the ice shelf to this pinning point. The lack of sea ice on the north facing ice front is also noteworthy.

It appears that ice shelf thinning is the key pre-conditioning factor for collapse. The mechanisms for ice shelf thinning include basal melting, meltwater production and rift development. These are interrelated mechanisms that pre-condition the ice shelves to collapse. This will be a key area of continued investigation to understand this critical process for the Antarctic Ice Sheet. At the moment it seems that the key process to rapid calving events is the rift development. Rift development is observed to begin at points of natural weakness. For both ice shelves prior to collapse an expansion of the area where rifts exists has been observed. In both cases this seems to result from pre-conditioning via thinning due to basal melt and surface melt. Rifts development is accentuated by water filling crevasses. A new study will be looking at the impact of reduced sea ice at the front as well (Scambos and Massom, 2008). It is obvious that the glaciologic community will be watching the Wilkins Ice Shelf next Austral summer.

References:

Rignot, E., Casassa, G., Gogineni, P., Krabill, W., Rivera, A., and Thomas, R. (2004). Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B Ice Shelf. Geophysical Research Letters 31: L18401, doi:10.1029/2004GL020697.
Scambos, T., Hulbe, C., Fahnestock, M. and Bohlander, J. (2000). The link between climate warming and break-up of ice shelves in the Antarctic Peninsula. Journal of Glaciology 46: 516–530.
Scambos, T., C. Hulbe, and M. Fahnestock (2003). Climate-induced ice shelf disintegration in the Antarctic Peninsula. In: Domack, E., Leventer, A. Burnett, A., R. Bindschadler, R., P.
Vaughan, D. G., Marshall, G. J., Connolley, W.M., Parkinson, C., Mulvaney, R., D., Hodgson, D.A., King, J.C., Pudsey, C.J. and Turner, J. (2003). Recent rapid regional climate warming on the Antarctic Peninsula. Climate Change 60: 243-274, 2003.


177 Responses to “Ice Shelf Instability”

  1. 101
    Timo Hämeranta says:

    Re 97-99, please see

    Thomas, Elisabeth R., Gareth J. Marshall, and Joseph R. McConnell, 2008. A doubling in snow accumulation in the western Antarctic Peninsula since 1850. Geophys. Res. Lett., 35, L01706, doi:10.1029/2007GL032529, January 12, 2008

    Abstract

    We present results from a new medium depth (136 metres) ice core drilled in a high accumulation site (73.59°S, 70.36°W) on the south-western Antarctic Peninsula during 2007. The Gomez record reveals a doubling of accumulation since the 1850s, from a decadal average of 0.49 mweq y−1 in 1855–1864 to 1.10 mweq y−1 in 1997–2006, with acceleration in recent decades. Comparison with published accumulation records indicates that this rapid increase is the largest observed across the region. Evaluation of the relationships between Gomez accumulation and the primary modes of atmospheric circulation variability reveals a strong, temporally stable and positive relationship with the Southern Annular Mode (SAM). Furthermore, the SAM is demonstrated to be a primary factor in governing decadal variability of accumulation at the core site (r = 0.66). The association between Gomez accumulation and ENSO is complex: while sometimes statistically significant, the relationship is not temporally stable. Thus, at decadal scales we can utilise the Gomez accumulation as a suitable proxy for SAM variability but not for ENSO.

    Further, the IPCC estimates “Current global model studies project that the Antarctic ice sheet will remain too cold for widespread surface melting and is expected to gain in mass due to increased snowfall.”

  2. 102

    Re: #100

    Thank you, Chris!

    Re: #101

    The paragraph from the IPCC is rather cold comfort as the latest research shows a negative mass balance primarily from losses at WAIS, does it not?

  3. 103
    Timo Hämeranta says:

    Re # 102, Tenney, please see

    Helsen, Michiel M., Michiel R. van den Broeke, Roderik S. W. van de Wal, Willem Jan van de Berg, Erik van Meijgaard, Curt H. Davis, Yonghong Li, and Ian Goodwin, 2008. Elevation Changes in Antarctica Mainly Determined by Accumulation Variability. Science, published online before print May 29 2008

    Abstract

    Antarctic ice sheet elevation changes, which are used to estimate changes in the mass of the interior regions, are caused by variations in the depth of the firn layer. Here we quantify the effects of temperature and accumulation variability on firn layer thickness, by simulating the 1980–2004 Antarctic firn depth variability. We demonstrate that, for most of Antarctica, firn depth changes are of comparable magnitude as observed ice sheet elevation changes. The current satellite observational period (~15 years) is too short to neglect these fluctuations in firn depth when computing recent ice sheet mass changes. The amount of surface lowering in the Amundsen Sea Embayment revealed by satellite radar altimetry (1995–2003) is increased by including firn depth fluctuations, while a large area of the East Antarctic ice sheet slowly grew due to increased accumulation.

  4. 104
    Timo Hämeranta says:

    Further Re 102 Tenney,

    you refer to the study

    Rignot, Eric, Jonathan L. Bamber, Michiel R. van den Broeke, Curt Davis, Yonghong Li, Willem Jan van de Berg, and Erik van Meijgaard, 2008. Recent Antarctic ice mass loss from radar interferometry and regional climate modelling. Nature Geoscience Vol. 1, No 2, pp. 106-110, February 2008, online http://www.nature.com/ngeo/journal/v1/n2/pdf/ngeo102.pdf

    “Observed estimates of ice losses in Antarctica combined with regional modelling of ice accumulation in the interior suggest that East Antarctica is close to a balanced mass budget, but large losses of ice occur in the narrow outlet channels of West Antarctic glaciers and at the northern tip of the Antarctic peninsula.”

    Please notice Andrew Shepherd’s comment in Nature News Jan 13, 2008:

    “Shepherd cautions that Rignot’s three-point trend shouldn’t be projected decades into the future, because there’s reason to believe that the increasing amount of cold meltwater near the coast might slow further losses.”

    Finally please see also:

    Zhang, Jinlun, 2007. Increasing Antarctic Sea Ice under Warming Atmospheric and Oceanic Conditions. Journal of Climate Vol. 20, No 11, pp. 2515–2529, June 2007

    Abstract

    Estimates of sea ice extent based on satellite observations show an increasing Antarctic sea ice cover from 1979 to 2004 even though in situ observations show a prevailing warming trend in both the atmosphere and the ocean. This riddle is explored here using a global multicategory thickness and enthalpy distribution sea ice model coupled to an ocean model. Forced by the NCEP–NCAR reanalysis data, the model simulates an increase of 0.20 × 1012 m3 yr−1 (1.0% yr−1) in total Antarctic sea ice volume and 0.084 × 1012 m2 yr−1 (0.6% yr−1) in sea ice extent from 1979 to 2004 when the satellite observations show an increase of 0.027 × 1012 m2 yr−1 (0.2% yr−1) in sea ice extent during the same period. The model shows that an increase in surface air temperature and downward longwave radiation results in an increase in the upper-ocean temperature and a decrease in sea ice growth, leading to a decrease in salt rejection from ice, in the upper-ocean salinity, and in the upper-ocean density. The reduced salt rejection and upper-ocean density and the enhanced thermohaline stratification tend to suppress convective overturning, leading to a decrease in the upward ocean heat transport and the ocean heat flux available to melt sea ice. The ice melting from ocean heat flux decreases faster than the ice growth does in the weakly stratified Southern Ocean, leading to an increase in the net ice production and hence an increase in ice mass. This mechanism is the main reason why the Antarctic sea ice has increased in spite of warming conditions both above and below during the period 1979–2004 and the extended period 1948–2004.

  5. 105
    Hank Roberts says:

    “Fair and Balanced” wrote:

    > Ice floating on seawater (by definition
    > above the melting point of ice)

    What’s your source for this belief?
    Why do you believe it? Have you looked it up?

    http://www.google.com/search?q=water+temperature+below+sea+ice

  6. 106
    sidd says:

    Timo Hämeranta wrote in comment #104 at 17 June 2008 at 1108:

    Zhang, Jinlun, 2007. Increasing Antarctic Sea Ice under Warming Atmospheric and Oceanic Conditions. Journal of Climate Vol. 20, No 11, pp. 2515–2529, June 2007

    Thank you for directing me to this paper. If I read it correctly, Mr. Zhang has a model where increased Southern sea ice occurs together with increasing air and ocean temperatures, increased stratification and decreased upper layer salinity. I was hoping that the paper might contain some observational data on stratification and salinity, but I did not see any. Would you (or any one else) by any chance be aware of work in that area ?

    sidd

  7. 107
    Richard Wakefield says:

    NASA Mission Poised to Help Us Gauge Our Rising Seas
    http://www.nasa.gov/mission_pages/ostm/news/ostm-20080616.html

    “We know the basics of sea level rise very well,” said JPL oceanographer and climate scientist Josh Willis. But several critical elements still need to be resolved, he stressed. “Everything doesn’t quite add up yet.”

    For example, in a recent study, Willis, Chambers and their colleague Steven Nerem of the Colorado Center for Astrodynamics Research in Boulder, compared the amount of ocean warming during 2003 to 2007 observed by the Argo buoys with the amount of warming calculated by combining Grace and Jason-1 altimeter data. While the two measurements closely matched with regard to seasonal ups and downs, they didn’t agree at all on the total amount of warming. In fact, the Argo data showed no warming at all, while the combined Jason and Grace data did.

    This is a mystery to the scientists, which they hope to resolve soon. Willis added there is no observing system yet for the deep ocean, and it could hold some real surprises.

    The record of sea-surface height begun by Topex/Poseidon is now 16 years old. As the record grows longer with the continued health of Jason-1 and the launch of OSTM/Jason-2, some uncertainties about sea level rise are much closer to resolution.

    “We are getting a better understanding of our measurement systems and just how much we can trust our numbers,” said Fu. “We know that sea level is not rising everywhere at the same pace, and we are learning more every year about the natural variability in the ocean over short and long periods. We are learning more about the exchange of heat between the ocean and the atmosphere, the driving force of our climate.”

    So will we have disastrous sea-level rise? If so, when?

    We don’t know yet, said Fu, but he does not rule out finding the answer.

  8. 108
    Timo Hämeranta says:

    Re # 106 sidd,

    hope this one helps, a bit at least:

    Sigman, Daniel M., Samuel L. Jaccard and Gerald H. Haug, 2004. Polar ocean stratification in a cold climate. Nature Vol. 428, No 6978, pp. 59-63, March 4, 2004, online http://www.soest.hawaii.edu/GG/FACULTY/POPP/Sigman%20et%20al.%202004%20Nature.pdf

    Re 107 Richard,

    additionally please see the studies

    1) Wöppelmann, Guy, B. Martin Miguez, M.-N. Bouin, and Z. Altamimi, 2007. Geocentric sea-level trend estimates from GPS analyses at relevant tide gauges world-wide. Global and Planetary Change Vol. 57, No 3-4, pp. 396-406, June 2007, online http://ff.org/centers/csspp/library/co2weekly/20070809/20070809_06.pdf

    “5. Conclusions

    Munk (2002) stressed that the sum of climate-related
    contributions to sea-level change was low (0.7 mm/yr)
    compared to the observations over the last 50–100 years
    (1.8 mm/yr) by referring to this factor 2 difference as the
    ‘enigma’ of sea-level change. Since then, the more
    recent results now indicate a 1 mm/yr contribution from
    the melting of global land ice reservoirs (Mitrovica
    et al., 2006), as well as a 0.4 mm/yr contribution from
    the thermal expansion of the world ocean (Antonov
    et al., 2005). We show here an exercise of combining
    GPS and tide gauge results that reduces the global average
    sea-level rise to 1.3 mm/yr. This appears to
    resolve the sea-level enigma….”

    The important contribution of Wöppelmann et al. is the inclusion of land motions (e.g. postglacial rebound) to the sea level calculations and widening the observational area also to two additional regions, namely ‘Northern Europe’ and ‘NW North America’. All those together reduces the mean rise from 1,8 mm/yr to 1,31 ± 0.30 mm/yr in the last 100 years.

    2) Johnson, Gregory C., Sabine Mecking, Bernadette M. Sloyan, and Susan E. Wijffels, 2007. Recent Bottom Water Warming in the Pacific Ocean. Journal of Climate Vol. 20, No 21, pp. 5365-5375, November 2007, online http://www.pmel.noaa.gov/people/gjohnson/gcj_3m.pdf

    “… Rough estimates of the change in ocean heat content suggest that the abyssal warming may amount to a significant fraction of upper World Ocean heat gain over the past few decades.”

    Yes, “we are learning more every year about the natural variability in the ocean over short and long periods…”

  9. 109

    Sorry to use news media as sources, but I note acceleration in the year predicted for an ice free Arctic Summer.

    Today it is: “Arctic Ocean expected to be ice free this September. For the first time in 100,000 years.”

    In 2005, the prediction was 100 years – then in 2006 it was 35 years, and now 2008 for an ice free Arctic.

    Is there a source for tracking the changes in models? Or links to model updates? It seems like we need rapid updates.

    ===URL snips:=== this summer 2008 ========
    Researchers predict ice-free North Pole this year
    Nunatsiaq News | May 23, 2008 | JANE GEORGE
    Here’s the good news: this summer’s Arctic ice melt means an early start to the Hudson Bay shipping season.
    Forecasts show Coast Guard icebreakers will no longer be necessary for shipping to Churchill after July 16.
    That’s 15 days earlier than the average ice-free shipping date of July 31, which means re-supply barges should able to reach communities in Nunavut’s Kivalliq and Kitikmeot regions that much earlier.
    But the down side to the retreat of the Arctic’s thin ice cover is a 50-50 chance that the North Pole will become ice-free this September – for the first time in more than 100,000 years…
    http://www.freerepublic.com/focus/f-news/2021152/posts

    ======= 2006 ===========
    Abrupt Ice Retreat Could Produce Ice-Free Arctic Summers by 2040
    December 11, 2006
    BOULDER—The recent retreat of Arctic sea ice is likely to accelerate so rapidly that the Arctic Ocean could become nearly devoid of ice during summertime as early as 2040, according to new research published in the December 12 issue of Geophysical Research Letters…
    http://www.ucar.edu/news/releases/2006/arctic.shtml

    ======== 2005 =================
    Arctic Ocean Could Be Ice-free In Summer Within 100 Years, Scientists Say
    ScienceDaily (Aug. 24, 2005) — The current warming trends in the Arctic may shove the Arctic system into a seasonally ice-free state not seen for more than one million years, according to a new report. The melting is accelerating, and a team of researchers were unable to identify any natural processes that might slow the de-icing of the Arctic…

    http://www.sciencedaily.com/releases/2005/08/050824081334.htm

    ==========================

    Uh oh, I feel a graph coming on.

  10. 110

    Re #109

    Here is a link to Richard Pauli’s news story Researchers predict ice-free North Pole this year.

    Note that Mark Serreze is only implying that there may be no ice between the North Pole and the North Atlantic, not an ice free Arctic. He say that “… only 2.22 million sq km of ice – less than the size of Nunavut – will remain in the Arctic Ocean this September. This would be much less than the record low of 4.28 million sq km set in 2007.”

    There is another report on the Arctic ice from the BBC: Arctic sea ice melt ‘even faster’. But it may be a little premature. It seems to be based on this chart of Arctic Sea Ice extent, which does show a steeper decline in sea ice extent during April and early May, but for the last month the rate of decline recorded last year and this year have been virtually the same.

    The question is what will happen when the ice reaches the tipping point at the end of June and the retreat steepens?

    Cheers, Alastair.

  11. 111
    Cobblyworlds says:

    Alastair,

    That’s not a bad article, but Stroeve’s considerations are much more complex than just that chart. It’s worth reading the expert outlook submissions from Arcus, available as one pdf from here:
    http://www.arcus.org/search/seaiceoutlook/report_may.php

  12. 112
    D Price says:

    Reading the NASA-GISS website it seems that apart from the West Antatctic peninsula all the above average temperatures in the Antartic seem to happen in winter. In the SH summers it seems either normal or colder. Has anybody else noticed this?

  13. 113

    Re #83 Richard Wakefield

    You state:

    “Re 70: Ray, you have no clue who I am or what I understand, but instead of dealing with the evidence, you instead fall back on the default position of anyone who has their dogma questioned”.

    You seem to be stating your bias in a Freudian sense, that you are more interested in dogma than reason. Your problem may lie in the fact that your idea of evidence is to narrowly limited or narrowly scoped. Biased views are common, though not always contributive until weighed in the aggregate of understanding.

    Ray merely pointed out apparent gaps in your reasoning as stated.

    It is pretty easy to oversimplify any argument in discussing AGW due to the mass of data and developing understanding.

    As to your “Models are imperfect attempts to represent what is known and used to make predictions. All the hype about the alarmist future…”

    You are missing some points. Models are developed to help understand observations as understood. Models are then refined and confirmed to the greatest degree possible. Models are never perfect, because they are intrinsically models and a useful tool for understanding. Without models modern development would be more slow and we would likely live in a less technologically advanced world.

    The other part that seems to be missing in your argument is that the observations are becoming more revealing than the models. There is a lot of confirmation going on in the manifestation based on what was expected from the models.

    If you approach this from relevant holistic reasoning, you might actually see the potentials not only in the future but what is actually happening on the planet right now. There are a lot of pieces to this puzzle and it seems you are not examining enough pieces to make claims, which is the basic problem with your argument.

    Your last statement “the AGW community had to scramble to adjust their models because of the current no-warming trend since 1998″ indicates a fundamental misunderstanding of the short and long term implications of climate forcing, not to mention your negation of the fact that we are at the bottom of the 11.1 year solar cycle and were in La Nina last year. Less forcing would be expected to reduce the temperature positive forcing. And of course you need to recognize that the 1998 El Nino event was unusually strong which set up the short term trend line.

    Fundamentally, you need to understand that climate is not weather and that short term views to not imply long term trends.

    Here is what you can likely expect based on the observed trends and expectations. The solar cycle will go back up in positive phase adding .3 W/m2 to the forcing and we will have another El Nino event. Expect some records to be broken in the GMT over the next 3 to 7 years and the Arctic Ice to reach at or near zero ice in that period as well during the minimum ice phase of the melt cycle.

    Your final statement “Thus I ask again, what will it take the planet to do to falsefy AGW theory?” indicates a rather complete misunderstanding of this particular global warming event and its drivers outside of the natural cycles.

    There are a multitude of problems with the question.

    First: and most obvious, the planet can not falsify the AGW theory. Although I sort of understand what you are trying to say it’s kind of a weird question.

    Second: Since the observations and the models are in agreement on a wide array of assessment perspectives “the planet” can’t prove the AGW theory wrong.

    Third: It is fairly obvious you are merely barking up the wrong tree or you have not checked out enough trees in the forest of climate science. If you examine only a few trees in the forest rather that a relevant sampling of the trees in the forest, you not only will not see the forest through the trees, you can’t see the forest through the tree, so to speak… It is fairly obvious, based on the arguments you have presented that the forest is bigger than you think.

  14. 114

    Re #111 where Cobblyworlds Says:

    Alastair,

    That’s not a bad article, but Stroeve’s considerations are much more complex than just that chart. It’s worth reading the expert outlook submissions from Arcus, available as one pdf from here:
    http://www.arcus.org/search/seaiceoutlook/report_may.php

    Cobblyworlds,

    Thnks for the link to the full article. It is very interesting but the point I was trying to make was not about the imminent disappearance of the Arctic sea ice permanently. I was really trying to say that just as the Antarctic ice shelves collapse suddenly, so does the Arctic sea ice. Around about the end of Jult, the meltwater which has been forming pools, eats its way through the ice and the ice begins to retreat more quickly. The accelerating melt can be seen clearly last year on the chart I linked to.

    Annual acceleration is not so obvious because it has been averaged away, but it can still be detected. I wonder whether the Antarctic ice experts are aware of this common feature.

    Cheers, Alastair.

  15. 115

    Re: comments #102 and #103

    Dear Timo,

    First, thank you for supplying those leads. I would have thanked you sooner but I have been a bit under the weather (or climate, as the case may be).

    Second, I would like to call upon you, raypierre, Chris, and Hank to come over to Dot Earth where we are being besieged by the industry-paid denialists due to Andy’s recent hammering on the realities of climate change and then of course Dr. Hansen’s speech, today, not to mention that Andy raised the point of whether or not the oil and coal executives should be considered criminals against nature.

    Please help at:

    http://dotearth.blogs.nytimes.com/2008/06/19/seas-rising-and-warming-faster-than-realized/

    and the 3 or 4 other threads since that one.

    Thank you.

  16. 116
    Hank Roberts says:

    Tenny, if the NYT wanted a fact checker involved they’d provide one as a fair witness. Good science reference desk help isn’t hard to find. Whatever their business model is over there, education isn’t in it.

  17. 117

    Re: comment #116

    Dear Hank,

    Fact checking is not the point. We know that there are industry-paid bloggers whose purpose is to delay any action on reducing CO2 emissions. It is our responsibility to present the truth and combat their efforts, efforts that have been exceedingly successful for the past 20 years, as you may have noticed.

    We are not talking about a business model here. We are talking about the sad fact that public opinion has been so manipulated that most people have no idea that global warming is a matter of the utmost urgency for all of us.

    There are plenty of readers of Dot Earth who are newbies to this issue and don’t know what to read or believe or where to even start.

    I am not a trained scientist — I have to teach myself all of this from scratch, while many bloggers here at realclimate are immersed in this subject and have all the correct arguments at hand. Therefore, it is not that much of a burden for realclimate bloggers to help out, in my not so humble opinion.

    And, what, after all, is the purpose of the realclimate blog?

    If I can spend 10 hours a day trying to help these readers, then real scientists from realclimate could spend 30 minutes of their time, surely.

  18. 118

    Re: #117 Tenny

    You stated:

    “And, what, after all, is the purpose of the realclimate blog? If I can spend 10 hours a day trying to help these readers, then real scientists from realclimate could spend 30 minutes of their time, surely.”

    I’d be willing to bet the scientists are doing more than 10 hours a day on climate. So to ask them for another 30 minutes is more than you may think. Because it’s not just 30 minutes you are asking for. For them to review and track the issues in your blog would likely take much more than 30 minutes a day because to review arguments you have to review all the arguments.

    The scientists are busy doing what they need to do and have committed tremendous time and effort to getting it right. They are doing their best and generally I think their time is best spent on doing the science rather than chasing down every single blog argument.

    I can speak for myself and maybe others would agree. We can help by bringing the relevant arguments to the people in our sphere of influence such as your blog.

    Read, study, learn and go back and do your best to answer the questions or better yet, point them to the RC articles that deal with the question at hand. I think it is unfair to pose such a challenge to those that are already working so hard. Asking for 30 minutes a day is a lot.

    I tell everyone I talk to to go to realclimate.org. RC is the best climate science one stop you can find.

  19. 119

    Let me be a little more blunt here. I am self-employed. Since I gave myself the task of fighting the EXXON-financed denialists, 8 months ago, I have not worked for myself. This is my choice, of course.

    Don’t imagine that I am a johnny-come-lately to science. I started out in science but ended up with two master’s degrees in business, instead.

    It is not that difficult to come over to Dot Earth once in a while.

    You guys can carry on your polite genteel discussions here, although we all know that almost all of the denialist arguments have been completely debunked and now we are just getting into some of the finer points.

    Dot Earth is not my blog. It belongs to the New York Times. Apparently, EXXON considers it important enough to send over scads of people to confuse the issue in the public’s mind.

    Dr. Hansen issued a clarion call 20 years ago — since then the public has become even more confused.

    The onus is on all scientists to help. Time is short.

    The Wall Street Journal also has chat pages — this is one more venue that should be used.

    btw, it is Tenney, with two e’s

  20. 120
    Mauri Pelto says:

    Tenny I appreciate your tenacity in blogging. As a glaciologist it is my job to educate the public. I find this is not possible by blogging at Dot Earth, where the noise to signal ratio is just too high, it was not several months ago. Climateprogress.org may get there, but for now the signal is higher than the noise. For the post here on ice shelves, it took about 30 hours of scrutiny of the key articles, after twenty five years of work in the topic area, to put together this piece. This is time well spent I feel, but does not earn a scientist any professional points. I do spend 30 minutes a day reading the material at these sites to remain educated in the realms that are not my specialty. It is amazing how informative at least the links are provided by the blogging public.

  21. 121

    Tenney,

    One top scientist is speaking out, but not on blogs that are only read by at most a few hundred people. James Hansen has now woken up to the problem. See Warming Scientist: ‘Last Chance’ where he says:

    “We’re toast if we don’t get on a very different path,” Hansen, director of the Goddard Institute of Space Sciences who is sometimes called the godfather of global warming science, told The Associated Press. “This is the LAST chance.” [My emphasis]

    The problem is that most climate scientist do not see the dangers. They are wrapped up in their own little specialty and don’t feel qualified to speak outside their field. And those who post here just cannot bring themselves to believe that the situation is as critical as it is. For instance, David wrote in James Lovelock’s Gloomy Vision

    “No one, not Lovelock or anyone else, has proposed a specific, quantitative scenario for a climate-driven, all out, blow the doors off, civilization ending catastrophe. …I think in general the consensus gut feeling among small-minded working scientists like me is that the odds of such a catastrophe are low.”

    Yet Lovelock had written that we could be heading for a minor mass extinction similar to that which happened during the Paleo-Eocene Thermal Maximum, with the few human survivors living on along the Arctic coast.

    Good luck with you mission, but I doubt you will get much help from the scientists until they too see the dangers. And of course, their doubts undermine your advocacy as they add to support to the skeptical argument that the science is still undecided :-(

    Cheers, Alastair.

  22. 122
    Ray Ladbury says:

    Tenney, as a scientist who has tilted at my share of windmills of scientific ignorance, I sympathize. The problem is that on a source like dot Earth, posters are anonymous, so claims of expertise cannot be assesses. Moreover, the average reader in such forums is incapable of assessing who is really an expert. I do post there, but I’m afraid it’s a bit of a scientific cesspit.

  23. 123
    Ray Ladbury says:

    Alastair, I don’t think the problem is that scientists are unaware of the risk. Rather, they simply despair of making a difference in forums where any jackass can claim to be a frigging Nobel Laureate and where the average reader is scientifically illiterate. That is why sites like Realclimate and ClimateProgress serve as refuges for those who are serious.
    Science has never worked as an evangelical enterprise. Since it requires work for people to understand scientific truth, they need to have the commitment of seeking it out rather than having it broadcast to them.

  24. 124

    Re: #120 Mauri

    I appreciate your signal to noise analogy, and your work on a vary informative article :)

    I believe that the noise level is precisely what has kept the argument confused for the past 20 years.

    Increasing signal strength is happening on an individual basis but prescience is not the forte of a society inundated with noise. On an individual basis the signal is getting through. Reason and relevance and context are the keys I find work but one must be able to answer the questions and provide sources.

    Re: #119 Tenney

    I hear you. In fact I empathize with you. I also think that this is a great place for you to blog but if I were you, and I’m not, I would advise another tactic in your responses.

    Many people of their own initiative are dedicating time and energy to the issue of awareness. And time is short, but reasonable polite argument can go a long way.

    It’s a simple matter of continuing to answer the questions and thereby continually raising awareness of the issues at hand. Impolite arguments tend to put up walls and cause people to solidify their beliefs in a non-scientific position. I encourage you to be polite and address the arguments with the truth of what is known. I’m still learning too, it’s not like this ever ends.

    I read some of your posts on Dot Earth. You seem to be addressing issues with the politic rather than the science. In one post you say two people “are seen for the jokes that they are ” and in another you chastise someone saying “Do we need that type of remark here, really?” I think the old you can catch more flies with honey thing could help here. Always address a concern with the relevant answer and instead of fighting more people will have the opportunity to learn.

    You have a great opportunity. When someone says something, respond, but go to RC first and look up relevant articles and post the links. That would help lead people to review the argument themselves. Remember, it’s not just the people you are talking to but those that read the posts as well. When you respond, use the opportunity to reach more people with good information. I apologize if I sound to instructive but that has been part of my career. I only mean to encourage you and all to refine the argument in order to achieve relevant understanding.

    Re #121 Alastair

    You have made a good point. Scientists typically don’t speak outside their field (part of the training I believe).

    The dangers are reasonably obvious regarding expected trends when viewed through aggregate reasoning of relevant spheres of influence of the climate forcing.

    I continue to believe that individual awareness will drive the policy. More people need to understand the ramifications and as human history has pointed out, we are typically not prescient as a general rule.

    General awareness, in my opinion will lead to policy shifts. Unfortunately, waiting for this to occur only exacerbates the problem through additional climate forcing i.e. future warming due to forcing levels and oceanic thermal lag time and latent inertia.

    I have noticed even amongst my more conservative friends that it does sink in if one argues with real science and addresses the political arguments and the disinformation simultaneously; it just doesn’t go very fast due to the nature of beliefs v. lack of awareness of relevant knowledge in context.

  25. 125
    Abbe Mac says:

    John,

    You wrote “it just doesn’t go very fast …” but that is the problem. We have now run out of time!

    As Margaret Beckett said on the BBC’s Newsnight programme tonight everyone thinks that it is a problem for our children and grndchildren to solve, but it is we who are going to suffer.

    Taking a centrist attitude may be correct when making political decisions, but not if there is a catastrophe is looming.

    Cheers, Alastair.

  26. 126

    Re: #125

    Alastair,

    I fully agree with you.

    So I am working on some new strategies to get the relevant understanding out. I hope to be able to share that with you soon. The disinformation campaign has been very successful in America, Norway and Great Britain; and moderately successful elsewhere.

    This is a ‘Right Now’ problem!

    But if I yell at people that don’t agree with the relevant science, they will say I am an alarmist, close their minds a little more, and tell their friends John has gone off the deep end.

    Since those that are adamant about it not being human caused are the target for the relevant understanding, then the onus of responsibility is upon us to communicate in the most effective, therefore the most expedient manner to achieve the goal of understanding of the relevant science.

    But that is just my opinion.

    Best, John

  27. 127

    Re: 124

    Dear John,

    The Dot Earth blog is getting more than 200,000 hits per month now.

    My responses on Dot Earth tend to be related entirely to whether the person I am talking at has already posted 30 comments of BS in two days, whether I can detect that the person is a paid denialist (not difficult to figure out), whether the person is a newbee, and whether I am tired and out of sorts and/or just plain exhausted from repeating myself. The paid denialists will not be convinced by anything I write because they are not there for that. Yes, sometimes, I get pretty sharp with people, but only the paid denialists.

    I will tell you something else — the fact that I have come out very strongly has given other commenters the courage to come out and take a stand in their own way, albeit in a somewhat milder manner.

    I maintain a blog (just click on my name to see the reference blog) with relevant scientific data, graphs, abstracts, articles, sites, etc., and in my comments I often refer to the links in it or to the skepticalscience.com site. It is getting about 2000 hits per month now, which is nothing compared to realclimate, of course, but volume is growing rapidly.

    I am constantly perusing sites on the net in order to keep up to date on the research.

    I do not send people to realclimate because it is generally over their heads.

    I do, however, often send people to Tamino’s blog since he posts the best graphs of the data.

    We have only 6 months to try to get the truth out to the public and have them understand the absolute seriousness of the problem before the next president takes office because the next president needs to act during his “honeymoon” period.

    Even a new president is not going to do anything on climate change if the public is badly informed and against it.

    Dr. Hansen has really stuck his neck out and basically is hanging in the wind right now. Is the scientific community going to just leave him there?

    You would not even have to argue with any of the comments, all you have to do is post a comment saying that you are who you are and that you think that the time has come to get on with reducing emissions or we are all going to end up toast or whatever.

    That wouldn’t even take 30 minutes, it might take only 10.

    I think that any tenured professor who has ever taught an intro course should be able to make simple comments on Dot Earth that refute the paid denialists.

    If real scientists are content to sit back and let the fossil-fuel industry win this struggle, then there is not much hope for the rest of us.

  28. 128

    Dear John,

    The “Do we need that type of remark here, really?” was my way of nudging Steve Bolger who is an old-timer on Dot Earth, like myself — he made a comment that implied that more people would be committing suicide as a result of the hopeless of the situation — that type of comment is generally considered to be very bad form on Dot Earth and I was merely reminding him. I am reasonably sure that he knew exactly what I meant and took it to heart.

    I am certainly very rude to the denialists — they are not there to listen to anyone or to be persuaded. No doubt this puts off some readers while encouraging others. Usually, I back up what I say with data or sites or cites, but not always, depending on how much time I have.

    There are obvious skeptics who lack the knowledge and who are willing to become more informed. Some of them are even coming around or have completely come around. I treat them with kid gloves (well, generally). I invite them to take it offline and we discuss by e-mail.

    Long-term genuine, sincere skeptics who will not be convinced I leave entirely alone.

    Thus, my focus is on the paid denialists and the skeptics who are willing to learn.

    What is now required is a strong signal rising above the noise — one person cannot do it alone.

    But the time is now, and the time is ripe.

    If I did not believe this, I would not be here making this request.

  29. 129

    Re: #127

    Tenney,

    I think your on the general right track as far as getting the message out. I’m curious, do you actually have proof that there are paid denialists? I think maybe there are but I would not accuse anyone without proof. I just present the relevant data in context so people can see a better perspective.

    I’ve got a good track record. I can typically turn someone around in 5 to 15 minutes of Q&A. I know being rude does not work with anyone from my experience and what I have seen. I understand you are only rude to certain people.

    Maybe, rather than being rude though, you present the science in context for the argument at hand. It is always easy to have a spitting match of conjectures, but facts are pretty hard to refute.

    Mostly they present air-balls that can go nowhere anyway. So when they do, I just lay some concrete at their feet and let them decide if its solid or not. All I can say is that I have noticed that I make a lot of progress that way. You can do the same.

    I don’t know if I agree that Dr. Hansen has stuck his head out or not, maybe in some ways? but I know he is sitting on a mountain of data that supports his context in the argument and I don’t think it is possible for anyone to legitimately refute the claims. He is diplomatic and strong in his assertions and his perspective, as far as I can tell, has no holes in his statement. Personally, I think he is standing on very solid ground in the debate.

    The relevant scientists are not, in my opinion, content to sit back and let the fossil-fuel industry win this struggle. There is a good method occurring here and it is getting stronger every day. I predict that before November, we will see a sea change in understanding. That will be due to a multitude of reasons in my opinion but we are all here to help people understand so the political motivation is strong come next January.

    Keep bringing reason to the table and there will be little room for ignorance. I don’t think the battle will be lost just because relevant scientists did not blog on Dot Earth. It will only be lost if we give up reason itself. That’s not to say some scientists don’t blog there already as is noted above by Ray Ladbury mentioned in comment #122.

    Keep up the relevant arguments.

    best,
    John

  30. 130

    Dear John,

    It is well documented that Exxon is paying certain organizations, just google: marshall institute tobacco climate

    The paid deniers all use the same fallacious arguments — they are quite consistent about it. You can politely show them the error of their thoughts with complete cites and graphs and whatever, but they come back like bad pennies over and over again with the same stuff — one of their favorites is: “It’s the sun!” Another is: “the planet is cooling — no temperature increases since 1998″ or “It was hotter in 1934″ (for a complete list and their refutations, go to skepticalscience.com).

    It is also well known that certain right-wing strategists have been using psychological tactics to influence public opinion. These same tactics are being used by the fossil-fuel industry. Essentially, these involve inspiring fear in the reader — examples are: the economy will be destroyed by being forced to switch to new energy sources, and environmentalists want to effect a transfer of wealth.

    Then, there are the more subtle insinuations, e.g., we should all wait and remain calm until the science is settled, or we should wait because technological improvements over the next 20 years will doubtless solve the problem for us.

    Even more subtle are the ones who start out thusly: “I am a scientist and I think we should reduce CO2, but the science is not settled yet and we should be cautious — just look at the disaster of renewables from corn…” However, it soon becomes clear from the rest of the comment that the writer is no kind of scientist.

    Trust me — after 8 months of this, I have seen them all.

    Let me tell you something about Joe Q Public. It is not necessary to teach him the science. He just needs to see that people he can respect and look up to have come out in agreement and they speak louder than the denialists. Joe Q Public will remain ignorant. That’s OK.

    But he needs to see scientists taking a public stand.

  31. 131

    Re: 122

    Dear Ray,

    I have seen your posts, and believe me, I certainly appreciate seeing them.

    It is always clear to me that you know what you are talking about.

    That is a quality that somehow always comes through to the reader when the writer is confident of what he/she writes and has a certain ease of writing the science — however briefly.

    This quality cannot be imitated by someone like me.

    But there is one quality that comes through in my writing — and that is my sincerity.

    I hope you will continue.

  32. 132

    Re: #120

    Dear Dr. Pelto,

    Please forgive me for having usurped your post here. I arrived at your post because I am terribly interested in the subject you are presenting.

    I am sure you did take enormous care and time in writing this post. For one thing, you have explained a great deal, and for another, everything you write may be scrutinized by other scientists in your field (that could make anyone take an extreme measure of care).

    As a former technical editor for Elsevier Science Publishers, I know that it is sometimes difficult for authors of academic papers to write down their conclusions. Authors must go a bit beyond the quantitative results. Further, the main conclusion should be included in the abstract, for all to see. It is a bit risky. Scientific reticence can come into play.

    An academic career often requires care and patience and a certain reticence. The tenure-track system can mean 7 years of treading carefully.

    But, in the better departments, a spirit of cooperation is encouraged because it benefits everyone.

    So, I am here asking for help in encouraging the public to realize that there is a broad consensus, and that we must all put our shoulders together in a spirit of cooperation to bring about the necessary changes.

    – lest there be no one left in the future to hit those pubs…

  33. 133
    Mauri Pelto says:

    The latest collapse on May 30 and 31st of the Wilkins Ice Shelf represents the reduction in the width of the ice shelf connection between Latady and Charcot Island from 6 km to 2.7 km. That the connection is being reduced in winter, lends to betting on how long it will take for this connection to be lost and Charcot Island to be surrounded by open water for the first time in a long time. Once again it is the warming of the Antarctic Peninsula area that has led to ice shelf thinning, which primed the pump for structural weaknesses to propogate and the ice shelf to partially fail.

  34. 134
    Karsten J says:

    One issue I have so far never seen discussed is that ice core data and seabed-core data suggests that during the last interglacial – the so-called Eemian interglacial – the temperatures over the Greenland icecover were about 3-6 degrees C higher than now (according to a fresh study by Dahl-Jensen et al. which I heard about on the danish radio), the global mean temperatures probably about 2 degrees higher than now, and the global sea-level about 3-6 meters higher than now (fx. the scandinavian peninsula was an island, the Arctic ocean connected via Arkhangelsk-Ladoga to the Baltic sea to the west of St. Petersburg).

    http://www.nature.com/nature/journal/v404/n6778/abs/404591a0.html;jsessionid=E5A21CD4C92D94619D0C25D50B6C96F3

    But at the same time, the atmospheric CO2-level was only around 290 ppm, so the explanation for the then warmer earth can’t be greenhouse warming?

    http://en.wikipedia.org/wiki/Image:Vostok_420ky_4curves_insolation.jpg

    I haven’t found any other explanations, but I suppose the Milankovitch cycles, somewhat differing positions of the continents and a somewhat lower Himalaya fx. could be candidates, but still it remains a puzzle “Stage 5 problem
    The stage 5 problem refers to the timing of the penultimate interglacial (in marine isotopic stage 5) which appears to have begun 10 thousand years in advance of the solar forcing hypothesized to have been causing it. This is also referred to as the causality problem.”

    http://en.wikipedia.org/wiki/Milankovitch_cycles#Stage_5_problem

    I think the answers to this must be very important in our understanding of the natural climate processes. And still: the polar bears (or their immediate ancestors) seem to have survived this warmer earth, as they survived even the climatic optimum around 9-5000 years B.P. How much sea ice was in the Arctic ocean during the Eem and during the climatic optimum? In Norway, there were pine forests growing 200-400 meters above the present upper limit for forests.

    http://en.wikipedia.org/wiki/Holocene_climatic_optimum

    http://geology.geoscienceworld.org/cgi/content/abstract/36/5/359

    http://www.sciencemag.org/cgi/content/abstract/317/5834/111

    http://www.co2science.org/articles/V11/N19/C3.php

  35. 135

    Re: #130

    Tenney,

    You’re preaching to the choir. Trust me, after nearly 35 years of awareness of the issue and nearly 15 years of examining the issue and the last 6 years of dedication to learning the details, I am aware of their arguments. I decided, like you to become involved in helping people understand the argument so we can all make progress.

    If you want to know more about how to deal with the arguments, you might want to read some of my own posts on the matter.

    http://www.uscentrist.org/news/2008/global-warming-twenty-years-later-tipping-points-near/
    http://www.uscentrist.org/news/2008/target-atmospheric-co2-350ppm
    http://www.uscentrist.org/news/2007/nasa-arctic-ice-melting-faster
    http://www.uscentrist.org/news/2007/nasa-climate-approaching-dangerous-point
    http://www.uscentrist.org/news/2008/the-age-of-consequences
    http://www.uscentrist.org/news/2007/hot-air-in-media

    “Let me tell you something about Joe Q Public.” It is, in my opinion, absolutely necessary that they understand the science, it is necessary for ‘you’ to understand the science.

    If you want to ‘sincerely’ participate in bringing awareness on this issue your success will only increase when you become more aware of the actual arguments and the science that refutes those arguments. Otherwise you will stay in a fight where both sides are throwing air-balls at each other and now learning or awareness is occurring.

    Please learn the science and share it and you will see greater success. Even Kim will eventually start listening to you. It will be obvious to all soon enough.

    I have posted two comments on the Dot Earth blog in the latest article on Hansen. Please stop begging to a crowd that is fully dedicated to the science and the argument. They are doing what they need to do. You need to study the science and get the word out and stop asking others to do work you can do. Sincerity only goes so far.

    There are two arguments: one is political and full of hot air; and one is science and full of observations, facts and modeling. Stick to the science. The more you participate in throwing air-balls the slower awareness happens. You are merely helping the opposition in my opinion.

    Please don’t get me wrong, I am not saying don’t participate. I am saying participate in a more informed fashion. That will help a lot. Don’t be lazy. You can learn this too. It’s not that hard and this is the best site to learn on. You have a lot of passion and yes, sincerity. That can go a long way, but not all the way. Everything you need is right here.

    Best,
    John

  36. 136

    Re #134 Karsten

    I thought the same thing at one point. My thoughts are that it has more to do with the amount of time spent at a particular forcing level. i.e. the longer the system spends at the forcing result of 290ppm the more sea level rise you get. But I am probably oversimplifying.

    Since we are at 1.9 W/m2 now and Co2 has a long atmospheric lifetime, we can expect continued warming and continued sea level rise for quite some time.

    In a complex interaction of systems, it is far to easy to say it “can’t be greenhouse warming” The picture needs to be examined from multiple angles to get a good idea of the drivers and their effects.

    Hopefully, someone more knowledgeable than myself may add to this.

  37. 137
    Hank Roberts says:

    Karsten J Says:
    26 June 2008 at 11:23 AM

    > One issue I have so far never seen discussed is
    > … the so-called Eemian interglacial …

    Karsten, this may help you see those prior discussions:

    Put the word “Eemian” into the Search box at the top of the page, and you’ll be shown all mentions; from that list or by doing more focused searches you’ll find discussion of most if not all of your questions here in prior threads.

  38. 138
    Karsten J says:

    Re# 136: Yes, it’s far more complicated than that, I think. Even if the warm Eem earth wasn’t a result of an enhanced greenhouse effect, that doesn’t mean that our present fast global warming isn’t a result of enhanced greenhouse effect either. As I said, the positions of the continents were somewhat different from now, maybe leading to at different regime for the ocean currents (ex. land-bridge between Asia and Australia? Further distance between South America and Antarctica? Small differences can lead to big consequences, when the system passes a threshold). Or (and) maybe the collapse of the Elsterian Ice sheets, which were far bigger than the Weichselian, created a different response involving positive feedbacks leading to the disappearance of the southernmost part of the Greenland ice-sheet and thus a higher sea-level, again propagating higher temperatures in some places, fx. because of the sea around Scandinavia meaning a lesser continental climate there.

    “The warmest millennia of at least the past 250,000 years occurred during the Last Interglaciation, when global ice volumes were similar to or smaller than today and systematic variations in Earth’s orbital parameters aligned to produce a strong positive summer insolation anomaly throughout the Northern Hemisphere. The average insolation during the key summer months (M, J, J) was ca 11% above present across the Northern Hemisphere between 130,000 and 127,000 years ago, with a slightly greater anomaly, 13%, over the Arctic.
    Greater summer insolation, early penultimate deglaciation, and intensification of the North Atlantic Drift, combined to reduce Arctic Ocean sea ice, allow expansion of boreal forest to the Arctic Ocean shore across vast regions, reduce permafrost, and melt almost all glaciers in the Northern Hemisphere. Insolation, amplified by key boundary condition feedbacks, collectively produced Last Interglacial summer temperature anomalies 4–5 1C above present over most Arctic lands, significantly above the average Northern Hemisphere anomaly. The Last Interglaciation demonstrates the strength of positive feedbacks on Arctic warming and provides a potentially conservative analogue for anticipated future greenhouse warming.”

    (“Last Interglacial arctic warmth confirms polar amplification
    of climate change” by Cape Last Interglacial Project Members, january 2006, Quaternary Science Reviews…)

  39. 139
    Chris Colose says:

    The high northern latitudes clearly warmer in mid-Holocene a few thousand years ago and during the last interglacial (Eemian) than recently, for orbital reasons (more summer sunshine). Globally averaged harder to call-—still a lot of uncertainties in southern reconstructions. Dahl-Jensen probably cites Cuffey et al. 1995 as some of the first really reliable borehole thermometry for that. The Greenland response to the warmer conditions in summer was retreat behind modern position, poorly constrained (hard to look back under the modern ice sheet to see where it went in the past!), and sea levels 4 to 6 m higher… During the Mid-Holocene, at least one published estimate of perhaps 0.5 m of sea-level equivalent lost from Greenland (given changes occurring in Antarctica and the last remnants of the Laurentide, hard to look at the global sea-level record and see that amount) and perhaps kilometers to tens of kilometers retreat beyond modern position. If you get this much with a bit warmer Greenland, and you’re talking about futures that involve several C to perhaps up towards 10 C for the Greenland vicinity, and with the general physical relation that the warmer it is, the more influential temperature becomes (if you have no melting on top, the ice at the shelf edge, then a bit of warming may do nothing; if you have the ice almost too warm, and warming causes a bit of thinning that lowers the surface and warms more, there is a threshold beyond which the ice sheet cannot survive, so in general the effect of a 1C warming is expected to be larger if the temperature before the warming is higher), you can see why there is concern. Arctic sea ice is also retreating rapidly, with 2007 hitting the record low.

    The skeptics love to say “It was warmer in Greenland in the past” and it was. And the ice sheet responded. Greenland actually doesn’t care who makes it warm or why it is warm, warmer conditions make the ice smaller, and too warm makes the ice go away. If it comforts people to know that Greenland was warmer before and it retreated, and that sea levels were higher, then so be it…

  40. 140

    Re: #135

    Dear John,

    I think that you must have seen only a very small sample of my comments of Dot Earth because it is well known by the old timers that I almost always back up what I say with the science and links to the research.

    In fact, you can see this by the early comments on Andy’s latest post:

    http://dotearth.blogs.nytimes.com/2008/06/26/23005-comments-and-counting-your-five-favorites/

    Lately, because I also have a background in business, I have focused less on the science and more on pension fund managers because public opinion matters very much to them.

    You will be hard pressed to find anyone on Dot Earth, paid denialists included, who doubt my sincerity or my credibility. (N.B. kim is not there to be convinced of anything — kim is there to sow confusion.)

    Have a look at my blog, which I use as a reference since my memory is horrible. Just click on my name — there are over 200 posts of relevant scientific information, graphs, etc.

    I have studied science since I was young child. I have never stopped studying it. This has stood me in good stead as I continue to perform what I consider to be my moral duty.

    I am only one person, living in the middle of nowhere in a developing country, far from research libraries, with no access to online subscriptions to Nature or Science. I just do the best I can. I am not asking anyone to do my work for me, as you put it.

    I do also disagree with you on educating the public. In the last fifty years, we have actually gone backwards on science education — it is not reasonable to suppose that we now have time to educate the general public in climatology. But, we do still have a small window of opportunity during which we must inspire and lead the general public to the conclusion that urgent and strong action is necessary, else we are all lost.

    If scientists who are familiar with climatology do not see themselves as taking part in this process, then what has all the research been for?

    But, I think that I have imposed on the hospitality of realclimate for long enough with this very off-topic discussion. I do thank our hosts for their consideration, and I apologize to Dr. Pelto for going so far off topic.

    p.s. You don’t know me, so I will just let you know that just about everything tickles my funnybone, so I had to chuckle when I read your comment saying that I should not be lazy. Since I began this quest, I have been here at the PC, 7 days a week, from morning until 2 or 3 a.m., reading, writing, posting, learning, communicating, getting up to speed, all unpaid work, to the point that my right arm is fairly useless at the moment, and I have had to become ambidextrous. Somehow, in my mind, that gives me the right to ask people here at realclimate to spend 5 minutes giving a show of public support at Dot Earth.

  41. 141

    Dear Ray,

    I have seen your comments on Dot Earth and they are very important. The more the better.

    Part of my objective is to get the NYT off the fence. Recently, the NYT has shown itself to be quite sensitive to certain criticisms that have appeared in Dot Earth comments. The NYT is hugely influential and can move public opinion. And, we must move public opinion or politicians will not be able to move on the necessary actions to limit CO2 emissions. It is as simple as that, and now is the time, the only time we have left. (I am not a university professor, so I can say that out loud.)

  42. 142
    David B. Benson says:

    Karsten J (134, 138) — The Eem was only 125,000 years ago so the positions of all land masses and the height of major mountain chains were essentially the same as now. AFAIK, interglacial 4 was warmer than any of the following three, and of course interglacial 2, the Eem, was warmer than now.

    There is a reconstruction of the Greenland ice sheet during the Eem copied into one of the IPCC AR4 FAQs (I think). It didn’t all melt, just enough so that between GIS and WAIS, the sea highstand was about 5 meters higher than now.

    Despite the so-called 10,000 year problem, which may solely be the result of improper dating of ice cores, there is no reason to suspect anything but orbital forcing and a lot of time: I have a 5766 year segment of the Vostok ice core analysis by Petit et al. centered at the climatic optimum of the Eem. The CO2 concentration starts, in my segment, at 240.4 ppm, rises to 287.1 ppm 3390 years later and then declines to 267.1 ppm at the end of my segment.

    That’s over five millennia, almost six, when melt could have exceeded accumulation at GIS and WAIS. I don’t have any more details.

  43. 143

    Re: #138 Karsten

    Also, generally and as I’m sure you know, Co2 is typically not the primary climate driver in the natural cycle but a result of the warming in the cycle shift (Milankovitch cycles + plus other effects but likely, mainly the cycles mentioned).

    It is only in this current warming event that Co2 has become a primary driver due to the large scale imbalances imposed on the system of all industrial GHG’s. Co2 is namely a larger culprit due to atmospheric time scale.

    I would love to see the alignment of the eccentricity, obliquity and precession cycles for the last interglacial. That might paint a clearer picture of the extended warm period and associated sea level rise.

    On our current interglacial: with current forcing pushing 2 W/m2 v. the last interglacial which looks to have peaked around .7 W/m2 combined with oceanic thermal inertia lag time and the time scale it takes to absorb the additional forcing.

  44. 144
    Nick Barnes says:

    Anyone interested in Arctic sea ice, check out this MODIS image from today:
    http://rapidfire.sci.gsfc.nasa.gov/realtime/single.php?2008178/crefl1_721.A2008178050500-2008178051000.500m.jpg
    This is the Arctic Ocean, down into the northern parts of the East Siberian Sea and the Chukchi Sea. The pole is roughly on the left-hand edge of this image; the centre is at maybe 80N. All of this sea should be covered with solid ice.
    Look at the character of the ice around the centre of the image.
    Anyone want to bet this ice will still be there in a month?

  45. 145

    Karsten,

    The explanation for the 10,000 year lead may lie here:
    Southern Hemisphere and Deep-Sea Warming Led Deglacial Atmospheric CO2 Rise and Tropical Warming There is a 21,000 year Milankovitch cycle which lead to warmer NH then SH summers every 10,000 years. The warm SH starts the deglaciation when the Antartic sea ice retreats, and the Pacific warms giving off more CO2. When the NH warms the CO2 causes the ice sheets to retreat, which releases water vapour and together with more methane causes the ice sheet melting to accelerate. There is also an ice albedo effect. The trigger is the Milankovitch cycle, but CO2, CH4, and albedo all act as amplifiers.

    HTH,

    Cheers, Alastair.

  46. 146
    Phil. Felton says:

    Re #134 Karsten

    “But at the same time, the atmospheric CO2-level was only around 290 ppm, so the explanation for the then warmer earth can’t be greenhouse warming?

    http://en.wikipedia.org/wiki/Image:Vostok_420ky_4curves_insolation.jpg

    Your graph shows a rise in CO2 at the beginning of the interglacial from ~200 – 280 ppm that’s a bigger change in forcing (log(CO2)) than from pre-industrial to now. So yes GHE should be part of the explanation.

  47. 147

    Tenney,

    I admire what you’re doing, though I don’t understand how you’re supporting yourself while doing it — savings? A pension? A private income? None of my business and I don’t really care what the exact answer is, but I’m glad someone’s doing what you’re doing.

    I’ll try to take a look over there and see what I can add.

  48. 148
    sidd says:

    Does anyone have a link to the presentation referred to in the article
    http://www.abc.net.au/science/articles/2008/06/25/2283071.htm?site=science&topic=latest

    tanx
    sidd

  49. 149
    Ron Taylor says:

    Tenney, I want to ditto Barton’s appreciation for your efforts. I check your site every day and often find useful information.

  50. 150

    Re: #148

    That is a sort of “alarming” article.

    Can someone give us info on the state of the WAIS during the last interglacial when sea levels were much higher than they are now?

    Thanks


Switch to our mobile site