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Is Antarctic climate changing?

Filed under: — eric @ 25 August 2006

Is the Antarctic ice sheet getting bigger or smaller? Is it warming or cooling?

As we’ve reported in earlier posts (here and here), getting accurate answers to these questions is non-trivial, because the available instrumental data remain sparse and generally date back only a few decades, at best. While modern satellite-based techniques such as laser altimetery and gravity anomaly measurements provide important information on very recent changes, to get at the longer term we must rely on less direct methods. In the last 5 years or so, an effort has been under way, much of it under the banner “International Trans Antarctic Scientific Expedition” (ITASE), to do this by collecting many dozens of ice cores from across the Antarctic continent. Two papers out this month represent the first major compilations of results from these efforts. The first, in Science on August 11th, provides a new estimates of Antarctic snowfall changes over the last 50 years. The second, in Geophysical Research Letters (August 30th) provides the first statistical reconstruction of Antarctic temperature change, extending about 200 years into the past.

In the Science paper, Monaghan and others show that there has been no significant change in Antarctic snowfall in the last ~50 years. This is a potentially important result because most calculations suggest that as the globe warms, polar snowfall should increase, somewhat mitigating the sea level rise that is expected to result as the margins of the ice sheets melt and thin. The new results differ from those of Davis and others, who used data from the European Remote-Sensing Satellite (ERS-1) and ERS-2 satellite altimeters to estimate that the Antarctic ice sheet had gained enough mass between 1992 and 2003 to slow sea level rise at a rate of about 1 cm/century. The two sets of results are not necessarily in conflict, but do suggest that the intepretation of Davis et al. that the observed change is due to snow accumulation increases may need revision. [See also our earlier post on the use of gravity measurements to determine mass changes in the Antarctic, here. There are also some new results on mass change in Greenland, reported by Chen et al., out last week in Science Express (here), based on measurements from the GRACE satellites, essentially confirming earlier results of major changes on the Greenland ice sheet.]

Monaghan et al.’s estimates are based on a clever combination of ice core measurements of annual snow layer thickness, and model determinations from the ERA-40 climate model Reanalyses. The reason for using both observed and model data is that, while the sixteen ice cores they use come from all over the Antarctic continent, they nevertheless remain only point sources of information. To obtain useful averages over broad geographic regions, it is necessary to interpolate between the different ice core records. Monaghan et al. use the model results to guide this interpolation. The technique is not dissimilar to other climate field reconstruction methods that we’ve discussed frequently on RealClimate. The chief difference is that Monaghan use the output of a climate model, rather than direct observations, to determine the patterns of covariance in the climate field (in this case, snow accumulation rate). This technique allows Monaghan et al. to extrapolate the model results (which are realiable only for the period 1985-2004) back in time as far as the last International Geophysical Year (IGY), 1957, with a great deal of confidence.

Extrapolated to the future, a possible interpretation of Monaghan et al.’s results is that sea level rise in the future would be even greater than otherwise expected. However, we caution that such extrapolation is probably not warranted. After all, the relationship between temperature and snowfall is based on physical arguments and atmospheric dynamics calculations, not only on data; just because we cannot yet detect an increase in snow accumulation does not mean that it will not happen in the future. Furthermore, while Southern Hemisphere temperature have increased, on average, along with the rest of the globe during the last century, the data are rather sparse at the higher latitudes. And although there is evidence for warming in the mid troposphere over Antarctica from radiosonde data over the last 30 years, it is also clear from satellite data that surface temperatures decreased during the years 1982 through 2002. In fact, one can make the case that the timing of accumulation changes agree rather well with the observed timing of surface temperature change in the Antarctic. Monaghan et al.’s results shows that while there has been no net change, snow accumulation actually increased from IGY until the mid-1980s, and decreased thereafter. Similarly, a simple average of the weather station data show the same pattern for temperature — average warming prior to the mid 1980, and average cooling thereafter. [And as we have reported previously, the recent cooling is quite well understood and not expected to continue over the long term.] It is thus premature to conclude (as the paper does) that we may need to revisit GCM assessments that show increased precipitation over Antarctica in conjunction with projected warming in the future.

The results of the Geophysical Research Letters paper by Schneider and others — on which I am second author — are relevant here. We’ll report on this at greater length once the paper is published. As Monaghan et al. did, we used ITASE ice core records. In this case, our goal was to determine temperature, rather than snow accumulation history, and we used the available Antarctic weather station data (much more complete for temperature than for accumulation) rather than model results. We found that the stable isotope composition of the ice cores mimics the observed temperature pattern — warming between the 1960 and 1980s, cooling since then. Using the stable isotope records to extrapolate farther into the past, we find that Antarctica has warmed, on average, in the last century, along with the rest of the globe. Once the accumulation records have been extended, it will be possible to revisit the relationship between temperature and accumulation trends. I suspect that there will not be any surprises here.


73 Responses to “Is Antarctic climate changing?”

  1. 51
    Jeff Weffer says:

    For anyone interested, here is a link to two visible satellite pictures of the sea ice in the Beafort Sea on July 25, 2006 and 2005. The sea ice is still right up to the coast and Barrow Alaska is still ice-locked (only one month to go in the melt season.) The 2006 sea ice extent is larger at this particular location than 2005 for example.

    http://earthobservatory.nasa.gov/NaturalHazards/shownh.php3?img_id=13738

  2. 52
    Steffen Christensen says:

    Hello, Gerd (#50). Many thanks for the comments! I have to humbly apologize to you, in that my comment (#15) appears to have been misinterpreted.
    First, using data accumulated since your paper in argument is a little unjust, as your paper has no opportunity to respond. It’s new data after all. Some theories don’t work out. Some do. It’s still worth writing a paper about them, based on what you know so far – that’s how science advances. Through strawmen.
    Second, my comment about the mean temperature in Alaska was directed at Bryan’s comment (#3) where he said, “there has also been a slight average cooling trend in Alaska.” That sounded to me like a comment about the average temperature in Alaska, which you didn’t discuss in your paper. As you know, the trends are different for different regions of Alaska – on the Arctic Shore of Alaska (Barrow) the trend is strongly upwards; in Nome, Anchorage and Kodiak, the trend is more curvilinear; and Fairbanks and Juneau are more linear, but modest in slope. Different warming regimes seem to be involved, which is mentioned in your paper. Of course, it’s early days yet. Indeed, the curvilinear trends suggest that more warming is going on in the most recent period. One way to read the Alaska story might be “warm temperatures from 1977-86; cooling in 1987-2000; warming again in 2001-2010″. Only time will tell.
    Third, my choice of time windows for demonstrating warming in Alaska had two purposes – first, to show that by choosing some of the free parameters in climate appropriately, you can make whatever story you like seem true. Second, to compare against the more recent climate (2001-2006) considers only data used since the last date of your paper, as a quasi-independent test of whether the analysis holds up to the more recent data. I chose 1977-1987 as a starting point so that it would be reflective of the conditions at the start of the “cooling period” mentioned by Bryan.
    Finally, I thank you for your intellectual honesty in admitting that the recent temperatures in Alaska have been quite high. That fact makes my chart of #15 possible.

    By the way, do you know why several of the climatological stations in Alaska are being retired? The data center at NASA/GISS ( http://data.giss.nasa.gov/gistemp/station_data/ ) reports that the stations at Nome and Kodiak have stopped getting new data as of 2004, and many other smaller stations since 2001. I find this an extremely distressing trend, since the ability of the climate researcher community to understand the climate is imperiled by less data. We need more data now, not less!

    Finally, to the moderators – my apologies for talking about Alaska again! I, for one, would love to read an article about the PDO and how it relates to global climate change. Alaska is a topical subject as well, since the North Shore is the bit of the U.S. that is warming the most strongly, hence the most relevant window into climate change for many Americans – most of whom do not own a passport. I know that here in Canada, our public didn’t start to get the picture until many documentaries on and interviews by the CBC in the High North. Now understanding is more-or-less universal outside of the Oil Patch and regions West.

  3. 53
    John L. McCormick says:

    RE #51

    Jeff, your link shows the Barrow coast on July 25 (date photo acquired).

    You do not know today’s condition of the Barrow shore line until you look at images (ca) August 29, 2006.

    [and Barrow Alaska is still ice-locked (only one month to go in the melt season.]

    And, such images are available today.

  4. 54

    Re #51 & 53 – Bob Grumbine of NOAA produces sea ice maps daily for both the Arctic and Antarctic. He has been archiving them since 1st July 1998, not long, and I have produced a couple of web pages where any three days of the maps can be compared.

    The Arctic sea ice maps are at http://www.abmcdonald.freeserve.co.uk/north.htm and you can see that today’s shows that the ice is still close to the shore of north Alaska, but this is unusual for this time of year. You can check this by clicking the back year button. However, it is just about obvious that the complete area of the Arctic pack of ice is less than it has been on this day of the year for any year since and including 1997. By comparing three ice maps equally widely spaced in time, the trend is fairly obvious.

    In contrast, today’s Antarctic sea ice maps show no observable trend. See http://www.abmcdonald.freeserve.co.uk/south.htm . One reason is that the Arctic ice is close to its seasonal minimum, whereas the Antarctic ice is close to it seasonal maximum. The maximum seems to remain fixed, even when the minimum decreases, although the Arctic maximum is now starting to show a small retreat. See http://nsidc.org/cgi-bin/wist/seaice_index.pl?hemis=N&img=plot&mo=03&scale=100& which shows the trend in Arctic ice for the month of March, close to the seasonal maximum.

    What is really interesting is that although the Arctic minimum (September) is decreasing strongly; see http://nsidc.org/cgi-bin/wist/seaice_index.pl?hemis=N&img=plot&mo=09&scale=100& Neither the Antactic maximum (September) http://nsidc.org/cgi-bin/wist/seaice_index.pl?hemis=S&img=plot&mo=09&scale=100& nor the minimum (March) http://nsidc.org/cgi-bin/wist/seaice_index.pl?hemis=S&img=plot&mo=03&scale=100& shows any sign of retreat.

    This sort of ties in with the message that the Antarctic snow is not changing, and nor is the Antarctic climate.

  5. 55
    John L. McCormick says:

    RE #54

    Alastair, thank you for the links.

    I use Dr. William Chapman’s CRYOSPHERE TODAY archive at:

    http://arctic.atmos.uiuc.edu/cryosphere/archive.html

    to view satellite images of Arctic ice extent. Scrolling down to Aug 29, 2006, I get a very clear impression that ice is quite a distance from the Barrow shore.

  6. 56
    Jeff Weffer says:

    The sea ice has left Barrow now but the point is that on July 25th, which is more-or-less the heighth of the summer, there is still pack ice at Barrow. Melting will occur and Barrow will be ice-free through August but then it will start freezing back in September.

    The point is, that Barrow is only ice-free for 1 and half months throughout the year. Media reports make it seem as though the entire polar ice cap is melting.

    Here is a live webcam of the Barrow coast (I didn’t link to it in my first post because it was still night-time.) Today in the light of day, there is still small pieces of ice floating out on the ocean.

    http://www.gi.alaska.edu/snowice/sea-lake-ice/barrow_webcam.html

  7. 57
    John L. McCormick says:

    Jeff, thanks for that great link to the Barrow shore line. I bookmarked it.

    I disagree with your opinion of the media reports. Nothing I have seen or read indicates the entire polar ice cap is melting. Rather, we know it is melting everywhere along the margins and interior. And, scientists having many years of observation-time logged, project a possible complete meltback by mid-century. I guess you have to be there to have that view.

  8. 58
    Lynn Vincentnathan says:

    I don’t know if this has any relevancy, but in the film IS IT HOT ENOUGH FOR YOU? (1989) a Banglore climate scientist explained that the ocean completes with the land for precipitation, and if the ocean warms (e.g., due to global warming), it could draw the monsoon rains (needed for agri) out over the oceans & precipitate there, causing droughts in India.

    Could the same happen re Antarctica? I know it’s a huge continent, bigger than the S. Asian subcontinent, so that might make a difference….as well as the typical wind patterns there, etc.

    In other words, even if we do get more precip (snow) with warming in Antarctica, could a large portion precip over the surrounding oceans, rather than land…

  9. 59
    ike solem says:

    After looking over the two papers, it certainly appears that Monoghan et. al have more comprehensive data coverage than Davis et. al; the regional variations in the East Antarctic seem more detailed in Monoghan et. al. See comment #1. It also seems that there is general agreement that the West Antarctic Ice Sheet is thinning; see the Perspective by David Vaughan on Davis et. al: http://www.sciencemag.org/cgi/content/full/sci;308/5730/1877

    So, the absorption of heat by the Southern Ocean on one hand would be expected to increase local atmospheric moisture, but the question is: Does that moisture makes its way into the East Antarctic Interior? Again, see comment #1 on the warmer=wetter? issue, and the need for atmospheric-ocean modelling.

    It is also worth referencing Michael Oppenheimer’s guest post on the topic of modelling ice sheets:
    http://www.realclimate.org/index.php/archives/2006/06/ice-sheets-and-sea-level-rise-model-failure-is-the-key-issue/

    “The limitations of ice sheet models were revealed starkly by the collapse of the northern sections of the Larson B ice shelf in 1998 and 2002. Glaciers bounded by the landward edge of the ice shelf accelerated toward the sea while glaciers bounded by the more southerly section of the ice shelf, which remained intact, didnâ��t. Apparently, backpressure on glaciers from the abutting ice shelf provides a significant portion of the restraining forces keeping land-based ice in place, at least in some instances. The recent behavior of glaciers farther south in West Antarctica, and in Greenland, points to a similar dynamical response to ice-shelf fragmentation.
    Many glaciologists regarded these observations as a clear test of the ability of ice sheet models to forecast dynamical changes in a warming ice sheet, a test the models failed.”

    To sum that up, there is limited data regarding what is going on in the Antarctic, and the ice sheet models haven’t predicted the recent dynamic changes. I can’t help but recall the rather vehement and derogatory statements that certain geoscientists were making about the prospects of rapid climate change some 5 yrs ago, based on the stability of the ice sheets. That’s all past history, yes? When the ice sheet dynamics are combined with the CO2 feed-forward effects of the melting permafrost and the increased wildfires in the Amazon and Noth America, it sure seems like rapid climate change is on the horizon. What will the end result of all this be?

    So, to expand the timeframe of this thread, which relates to recent climate change in the Antarctic: There are a few other recent reports that are helpful in understanding the dynamics of the West and East Antarctic Ice Sheet (WAIS and EAIS). The most recent cycle of global glaciation was initiated some 3 million years ago, when sea levels were higher (25m and 35 +/- 18m from coastal terraces and Pacific atolls, see Raymo et al below). The sum sea level equivalent stored in the Greenland and WAIS is 12-14m, so the EAIS must have been involved in sea levels in the mid-Pliocene, 3.3-3.0 million years ago, when temps were some 3 C higher then today. This period is of interest because that’s the temperature increase climate models predict, so future climate might look a lot like the mid-Pliocene. If this is the endpoint, how fast will we get there?

    The following papers address the issue of understanding why the 43,000 year glacial cycle (3-1 mya) transitioned to a 100,000 year cycle (1 mya-Holocene). Raymo et. al describes a transition from a terrestrial melting margin of the EAIS to a glaciomarine ice calving margin that coincides with the glacial cycle transition, while Huybers describes better methods of estimating Milankovitch-driven insolation effects (which relate primarily to the 3-1 mya period). Currently, >90% of Antarctic ice margins are marine; if sea level rise continues then the grounding margins will retreat, resulting in accelerated ice shelf disintegration, and eventual production of a terrestrial margin for the EAIS. Of course, the timescale of this is of great concern – 100 years? 1000 years? Eventually, the EAIS will start behaving like the Greenland Ice Sheet is today if warming trends continue as predicted. The EAIS is equivalent to 54-55m of sea level rise.

    What I’m reading in all this is that the last 5 years or so of data are indicating that the ice sheets are far more dynamic than anyone suspected, and the ice sheet models need to be adjusted to account for this in order to produce realistic climate predictions. The eventual predicted temp rise of 3C might be correct, but the response time of the climate system might be underestimated.

    Paillard:
    http://www.sciencemag.org/cgi/content/full/313/5786/455
    Raymo et. al:
    http://www.sciencemag.org/cgi/content/abstract/313/5786/492
    Huybers:
    http://www.sciencemag.org/cgi/content/full/313/5786/508

    Finally, what processes might set the upper bound on atmospheric CO2 in the warming world that we are entering? Here’s a guess: reduced thermohaline circulation due to less bottom water formation in the polar regions might set up an ocean system in which marine photosynthetically produced organic carbon is exported to the seabed instead of being recirculated back to atmospheric CO2. I suppose there would be evidence of this in seafloor sediment %organic carbon records from 3 Mya if this were true. This would prevent the ‘global runaway greenhouse’ and also links the climate system to biosphere activity – but that is assuming that all of the remaining fossil fuels in the ground are not converted to atmospheric CO2.

  10. 60
    Bryan Sralla says:

    Re #56, #57. Leffingwell and Mikkelsen surveyed the north slope by steam ship in 1907, stopping in Barrow, before sailing to Flaxman Island. I also believe that Alfred P. Brooks surveyed the coast by ship in 1904. It was common knowledge among these early explorers that one could spend a complete summer field season anchored off the coast, and sail out safely before winter. This might come as a surprise to some readers.

  11. 61
    ike solem says:

    RE#59,
    Sorry, I meant to say that the response time of the climate system might currently be overestimated due to the dynamic nature of the ice sheets.

    The notion of a photosynthetically driven ‘carbon-export pump’ in the global oceans has been around a while, for example see:
    Upper Ocean Carbon Export and
    the Biological Pump
    Hugh W. Ducklow, Deborah K. Steinberg
    Oceanography, Volume 14, Number 4, 2001

  12. 62
    Russ Hayley says:

    In the last 2 years that I have been subscribing to Newscientist, I have seen lots of articles that headlines like ‘Glaciers are retreating worldwide, ‘Greenland glaciers are growing’, ‘Greenland melt is accelerating’ ‘Antarctic ice melt defies warming theories’, ‘Antarctic ice growing’ etc etc. All seem to conflict with eachother but all are evidence for climate change. I even read recently that a Pakistani glacier was growing as a result of climate change!

    No consistency or there doesn’t seem to be to the layman. Therefore it just gets ignored and fuels the apathy.

  13. 63

    Off topic, but comments are closed on the post where I entered, via a link from cryoblog, to a comment to The Greenland Ice

    [... but is computationally very expensive and cannot yet routinely be done in 3-dimensional ice sheet modeling. --eric]

    I’d appreciate some details on the computational problem. Email is fine, or a follow-up comment. ebw at abenaki dot wabanaki dot net

  14. 64
    Brian Hartmann says:

    First of all, thank you to Gerd Wendler for adding his clarifying remarks. I have a few to add myself. In the interest of full disclosure, I am no longer at the Alaska Climate Research Center having relocated to the lower 48, but obviously I still have an interest in my and Gerd’s work and its interpretation.

    In regards to Comment #15: First off, the climate zones are not treated as equal-weight in trying to determine a “statewide” average temperature. In all reality, we prefer to work in the climate zones in the interest of trying to get away from blanket statements of averages and changes over an area like Alaska, with its myriad of climate influences, as well as its sheer size. That is why throughout the paper, we took great care to segregate the different ways in which each zone and each season (and in some cased, each month) was different prior to and subsequent to the shift.

    Also, in reply to Comment #15: “Picking an arbitrary high-water mark, here 1976, raises the possibility of a well-known statistical phenomenon of regression towards the mean. You can always make it look like the temperature is cooling by choosing a nice hot year to start your clock from – and only consider years subsequent to that.”

    I agree fully that cherry-picking of data and starting linear regressions in convienient years can yield misleading trends. Again, that was one of the motivating factors for the paper, to demonstrate that choosing to work ONLY in linear trends can yield “false-positives” so to speak.

    But contrary to your contention, 1976 WAS NOT an arbitrary choice on our part. It was a choice based in the real, physical and observed changes that occurred in the North Pacific and Alaska that year.

    In reply to Comments #20 and #21: Looking at a long-term linear trend (1950 to present) of various stations in Alaska does indeed show significant warming in most seasons. However, one motivation of the J of Climate paper was to see just how significant a part the “step-wise” jump observed in 1976 plays in those warming trends, which are cited quite often to explain things such as settling permafrost, retreating glaciers, etc.

    While it is mentioned in the comments that our paper does show that most of the regions in Alaska (with the obvious exception of the Arctic region) cooled from 1976-2001, I would also like to point out that all of the 6 regions in the study demonstrated cooling PRIOR to 1976 as well (Hartmann and Wendler, Table 9).

    As we state in our conclusion: “…the ues of trend line analysis in climate change research depends greatly upon the time period studied, and results can be biased when an abrupt climate change is observed during the study period. It has been demonstrated that the sudden changes of 1976 observed in Alaska have a profound effect on temperature trends.”

    The overall point I strive to make in all of this is that there has to be a more specific approach to looking at temperature change than linear analysis, seeing as how in the case of the last 60 or so years in Alaska, that linear analysis seems to be heavily influenced by non-linear changes.

    I welcome any and all to contact me if you have questions.

  15. 65
    Jeff Huber says:

    Shishmaref, Alaska is falling into the sea.

    Yea sur it is. The village is on a barrier bar and the bar is moving to the west. The village was a seasonal fish camp and a perment village should have never been build there. The location of the village was a poiltical decsion and the geologist who spoke up at the time were ignored. The rise and fall of sea level have nothing to do with the village “falling in to the sea”. The same is true for Kilivina

    Ps ice on the puddle this morning. at 66N

  16. 66
    Bryan Sralla says:

    Re: #60 sorry for the typo. That should be Alfred H. Brooks for all who are interested.

  17. 67
    Lynn Vincentnathan says:

    Re my #58 post, if precip (snow in Antarctica) does increase w/ warming, could a large portion of the precip (snow) be drawn over the warming oceans near Antarctica (which then would not help slow sea rise)?

    When I don’t get an answer, I assume scientists don’t really know one way or the other….

    [Response: It's not so much a matter of "not knowing" but of having to answer an ill-posed question. I'll get back to it with a longer answer, but the short answer is that if the ocean warms "near" Antarctica, it is going to result in more precipitation in Antarctica (as well as as over those warmer seas. --eric]

  18. 68
    Coby says:

    Re coastal erosion and Alaska, my understanding has always been that the primary cause is melting permafrost rather than rising sea levels.

  19. 69
    Jeff Huber says:

    The villages are on a barrier bar see link http://www.google.com/maps?f=q&hl=en&q=Kilivina+Alaska&ie=UTF8&z=7&ll=66.266856,-164.003906&spn=2.038696,7.404785&t=k&om=1
    Shisis located in the western part of the photo on the barrier bar near the small lagoon. Kilivina is on the western tip of the barrier bar near the white spot at the top of the photo.

  20. 70
    unconvinced says:

    Re:#32. You say that there is now less natural variability *assuming* AGW is taking place. Just as an exercise, assume AGW were *not* happening. Could the previous variability possibly show that current temps are in the range of natural variability? Do *any* climate reconstructions of the previous 5k years show trends similar to the current trends over similar time-scales? It’s just that it seems to me that we are observing changes with much greater accuracy now than any reconstruction can possibly provide, and calling it unprecedented – how can it be labelled as “unprecedented” under such conditions, with *no* (that I’ve seen anyway) conditionals attached (such as “it appears to be…”, “to the best we are able to ascertain…”). Perhaps this sort of thing *is* published in peer reviewed papers, but it most certainly is *not* in the mass media reports.

    The bottom lime is this: hard evidence, it seems to me, is sorely lacking in this debate, and some of the claims that have been made (on both sides) are, when investigated thoroughly, unsubstantiated.

    Regardless of whether you “believe” in AGW or not, we should *all* be bowing to the facts and acknowledging the uncertainties – if you promote conjecture as fact, it’s extremely easy to come “unstuck”, and even if you are actually correct, you will be dismissed as a crank. If anyone here truely believes that we humans are in for a hard time because of our lack of forsight (in terms of climate, please!) and that natural variability has *no* role in curent climate trends, than I think you are somewhat deluded!

  21. 71
    Grant says:

    Re: #70

    Believe it or not, we’re actually *glad* to meet skeptics whose doubt is based in reason.

    I’ll try to answer some of your questions, but I caution you that I’m not a climate scientist. I’m a mathematician, I specialize in the statistical analysis of time series, so on that topic I can speak authoritatively; but on other issues related to AGW, to paraphrase Will Rogers, I only know what I read in the peer-reviewed papers — and on RealClimate.

    Re:#32. You say that there is now less natural variability *assuming* AGW is taking place. Just as an exercise, assume AGW were *not* happening. Could the previous variability possibly show that current temps are in the range of natural variability?

    Actually, when statistical studies search for trends in the data, that’s *exactly* the assumption which is made: that there is no trend, only natural variability. Only when that hypothesis can be rejected as too unlikely to be believed, is the idea of a trend considered to be statistically significant.

    All available information about natural variability indicates that it cannot explain the current temperatures.

    Do *any* climate reconstructions of the previous 5k years show trends similar to the current trends over similar time-scales?

    None. However, there aren’t really any climate reconstructions for the last 5K years with anything near enough precision to perform a meaningful comparison. The furthest back in time that such reconstructions have been attempted with sufficient precision is 2K years.

    A recent study by the National Academy of Sciences addressed the question of the correctness of such reconstructions. They concluded that there is “high confidence” in reconstructions for the last 400 years, “less confidence” in reconstructions for the last 900 years, and “low confidence” in those extending further back in time. Despite low confidence in the most extensive reconstructions, all reconstructions were described as “plausible.”

    It’s just that it seems to me that we are observing changes with much greater accuracy now than any reconstruction can possibly provide, and calling it unprecedented – how can it be labelled as “unprecedented” under such conditions, with *no* (that I’ve seen anyway) conditionals attached (such as “it appears to be…”, “to the best we are able to ascertain…”). Perhaps this sort of thing *is* published in peer reviewed papers, but it most certainly is *not* in the mass media reports.

    Those are exactly the “conditionals” which are replete in the peer-reviewed literature. In fact, the use of such qualifications in the IPCC TAR (Intergovernmental Panel on Climate Change, Third Assessment Report) was used as an attack point by denialists, who even referred to such language as “weasel words,” implying that it was cowardice to state conclusions in those terms. Sometimes, in the court of public opinion, it seems as though you’re “damned if you do, damned if you don’t.” Omit such qualifiers, you’re accused of unrealistic confidence, include them and you’re accused of “weasel words.”

    The bottom lime is this: hard evidence, it seems to me, is sorely lacking in this debate, …

    It seems to me that there’s a great deal of very hard evidence. Keep reading this blog and you’ll see more and more of it.

    … and some of the claims that have been made (on both sides) are, when investigated thoroughly, unsubstantiated.

    I’m aware of far too many unsubstantiated claims on the “no-AGW” side of the debate; can you be more specific about unsubstantiated claims on the other side?

    Regardless of whether you “believe” in AGW or not, we should *all* be bowing to the facts and acknowledging the uncertainties – if you promote conjecture as fact, it’s extremely easy to come “unstuck”, and even if you are actually correct, you will be dismissed as a crank.

    On this, we agree.

    If anyone here truely believes that we humans are in for a hard time because of our lack of forsight (in terms of climate, please!) and that natural variability has *no* role in curent climate trends, than I think you are somewhat deluded!

    I truly believe it. My belief began when I became highly *skeptical* about AGW, so I decided to investigate in detail. I’m not a climate scientist, but I am a mathematician, so you have to get up pretty early in the morning to fool me with numbers. My researches have convinced me that AGW is very real and very dangerous — and my belief is based on hard facts.

    [Response:Grant, all very nicely said. I would add that NOBODY believes that natrual variabilty has *no* role in current climate trends. This is a strawman argument. -eric]

  22. 72
    Jeff Weffer says:

    Just noting that the sea ice is already freezing back in Barrow, Alaska.

    http://www.gi.alaska.edu/snowice/sea-lake-ice/barrow_webcam.html

    [Response:Notwithstanding your valid point that the media tend to over-state the amount of ice that is melting, it IS getting into fall at the moment. Some parts of climate are eminently predictable! See here for a bit of amusement on this subject. NOTE the date of the article please!--eric]

  23. 73
    Grant says:

    Re: response to #72

    Thanks for the link! I’d missed that the first time out. I got a real good belly laugh out of it.


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