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Major analysis finds “less ice covers the Arctic today than at any time in recent geologic history.”

By Joe Romm  

"Major analysis finds “less ice covers the Arctic today than at any time in recent geologic history.”"


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Paleoclimate study: “the Arctic temperature change consistently exceeds the Northern Hemisphere average by a factor of 3-4″

A first-of-its-kind analysis, “History of sea ice in the Arctic” (subs. req’d), by an international team of 18 top scientists led by Leonid Polyak concludes:

[E]pisodes of considerably reduced sea ice or even seasonally ice-free conditions occurred during warmer periods linked to orbital variations. The last low-ice event related to orbital forcing (high insolation) was in the early Holocene, after which the northern high latitudes cooled overall, with some superimposed shorter-term (multidecadal to millennial-scale) and lower-magnitude variability. The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.

The key point is that the Arctic loses ice when it is forced to lose ice.  In the past that was driven by orbital changes, and now it is being driven by human emissions.

This Quaternary Science Reviews paper is based on a detailed study of “proxy records from the Arctic Ocean floor and from the surrounding coasts.”  You can find a brief discussion of those methods in the Ohio State University news release here, which explains this is “the first comprehensive history of Arctic ice.”  The analysis “re-examined the data from past and ongoing studies — nearly 300 in all — and combined them to form a big-picture view of the pole’s climate history stretching back millions of years.”

I asked the lead author, Leonid Polyak, of Ohio State’s Byrd Polar Research Center, when was the last time the Arctic was ice free.  He replied:

The paleo data we have so far is very scant, so we can’t know for sure when the Arctic was ice free in the summer last time. To be conservative, the closest candidate is the early Holocene (roughly ~10 kyr ago), when the insolation in the Arctic was high due to the beneficial orbital configuration; however, the more data I see, the stronger is my impression that there was not that little ice at that time. The next best (actually, better) candidate is the Last Interglacial, about 125kyr ago, again due to orbitally-driven high insolation: the ice was likely very low, but we can’t say whether it was completely ice free in summer or not. There are also a few other major interglacials, which may have had a similar picture, in particular Marine Isotopic Stage 11, about 450 kyr ago. In any case we are talking about very rare events controlled by a forcing very different from today. If none of those intervals was really ice free, then a million year assessment would be correct.

The Quaternary Science Reviews piece, whose co-authors include Penn State’s Richard Alley and NSIDC’s Mark Serreze, explains why it was warm (and there was reduced ice) in the Arctic 11,000 years ago — and why it’s warm now with rapidly shrinking summer ice:

The present interglacial that has lasted approximately 11.5 kyr is characterized by much more paleoceanographic data than earlier warm periods, because Holocene deposits are ubiquitous and technically accessible on continental shelves and along many coastlines. Multiple proxy records and climate models indicate that early Holocene temperatures were higher than today and that the Arctic contained less ice, consistent with a high intensity of orbitally-controlled spring and summer insolation that peaked about 11 ka and gradually decreased thereafter….

Reviewed geological data indicate that the history of Arctic sea ice is closely linked with climate changes driven primarily by greenhouse and orbital forcings and associated feedbacks. This link is reflected in the persistence of the Arctic amplification, where fast feedbacks are largely controlled by sea-ice conditions.

So external forcings — primarily orbital in the past and primarily greenhouse gases now — start a process that is accelerated by polar amplification.

This was actually a special-themed issue of QSR, “Arctic Palaeoclimate Synthesis.”  It has a good piece just on that fast feedback, “Arctic amplification: can the past constrain the future?” (subs. req’d), which concludes:

Arctic amplification, the observation that surface air temperature changes in the Arctic exceed those of  the Northern Hemisphere as a whole, is a pervasive feature of climate models, and has recently emerged in observational data relative to the warming trend of the past century…. Here we evaluate the mechanisms responsible for Arctic amplification on Quaternary timescales, and review evidence from four intervals in the past 3 Ma for which sufficient paleoclimate data and model simulations are available to estimate the magnitude of Arctic amplification under climate states both warmer and colder than present. Despite differences in forcings and feedbacks for these reconstructions compared to today, the Arctic temperature change consistently exceeds the Northern Hemisphere average by a factor of 3-4, suggesting that Arctic warming will continue to greatly exceed the global average over the coming century, with concomitant reductions in terrestrial ice masses and, consequently, an increasing rate of sea level rise.

Now that should be alarming to anybody:

the Arctic temperature change consistently exceeds the Northern Hemisphere average by a factor of 3-4

And indeed the best recent models show staggeringly high Arctic warming this century if we stay on our current emissions path (see M.I.T. doubles its 2095 warming projection to 10°F “” with 866 ppm and Arctic warming of 20°F“).

As RealClimate noted in their useful discussion, “Polar amplification is thought to result primarily from positive feedbacks from the retreat of ice and snow.” Indeed, the popular explanation is that warming melts highly reflective white ice and snow, which is replaced by the dark blue sea or dark land, both of which absorb far more sunlight and hence far more solar energy.

But in fact Arctic warming is amplified for several additional synergistic reasons, which are worth knowing, as I discussed in “What exactly is polar amplification and why does it matter?

As the International Arctic Science Committee (IASC) explains in their 2004 report, Impacts of a Warming Arctic (see figure here):

  • In the Arctic, compared to lower latitudes, “more of the extra trapped energy goes into warming rather than evaporation.”
  • In the Arctic, “the atmospheric layer that has to warm in order to warm the surface is shallower.”
  • So, when the sea ice retreats, the “solar heat absorbed by the oceans in summer is more easily transferred to the atmosphere in winter.”

[And as one climate scientist explained to me, it can get incredibly cold above thick ice, but it can't get much colder than freezing above open water.]

All this leads to more snow and ice melting, further decreasing Earth’s reflectivity (albedo), causing more heating, which the thinner arctic atmosphere spreads more quickly over the entire polar region, and so on and on.

And that in turn threatens a cascade of effects. As the scientists at The International Polar Year explained last year, this could “speed up melting of the Greenland ice sheet, accelerating the rise in sea levels,” and “Permafrost melting could also accelerate during rapid Arctic sea-ice loss due to an amplification of Arctic land warming 3.5 times greater than secular 21st century climate trends” (see “Tundra 4: Permafrost loss linked to Arctic sea ice loss“).

Yet the destruction of a significant fraction of the permafrost must be avoided at all cost, since the tundra feedback, coupled with the climate-carbon-cycle feedbacks that the IPCC models, could easily take us to the unmitigated catastrophe of 1000 ppm (see Tundra, Part 2: The point of no return).  See also NSF issues world a wake-up call: “Release of even a fraction of the methane stored in the [East Siberian Arctic Shelf] shelf could trigger abrupt climate warming.”

One final point from the summary overview of the special issue of QSR:

Taken together, the size and speed of the summer sea ice loss over the last few decades appear anomalous compared to events from previous thousands of years, especially considering that changes in the Earth’s orbit over this time have made sea ice melting less, not more, likely.

Human-caused Arctic warming has overtaken 2,000 years of natural cooling, as a “seminal” 2009 Science study found” [see figure below]:

A Hockey Stick in Melting Ice


In short, “greenhouse gas emissions are overwhelming the system,” as David Schneider, a visiting scientist at the National Center for Atmospheric Research and one of the Science article’s co-authors put it.

So the next time some anti-science disinformer — or more likely, one of the doubters who has been duped by them — says past warmth undermines our understanding of human-caused warming, tell them, quite the reverse is true.  The paleoclimate record provides us more cause to be worried, not less.  We know natural forcings led to warming in the past, but human emissions of greenhouse gases are overwhelming the climate now, and threatening catastrophic levels of warming if we stay on our current emissions path.

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37 Responses to Major analysis finds “less ice covers the Arctic today than at any time in recent geologic history.”

  1. vukcevic says:

    According to what I am finding, it is not out of question that the Arctic stays relatively warm while certain parts of the north hemisphere get colder. I accumulated lot of info about the Greenland-Scotland ridge and its hydrology controlling the ‘in and out’ Arctic flow. It is all meter of the currents circulation and jet stream tandem:
    As warm waters inflow increases, keeping Arctic’s temperature up, so it does outflow of the cold currents. This shifts ‘jet stream’ further to the south in the NW Atlantic as it was the case in the recent months.

  2. Gee, guess it won’t be a good idea to all move to Canada after all.

  3. fj2 says:

    Deutsche Bank Climate Change Advisors
    Investment Research


    Download the paper here:

    ” . . . we asked our advisors at the Columbia Climate Center at the Earth Institute, Columbia University, to examine as many as possible of the major skeptic claims. . .”

    The paper’s clear conclusion is that the primary claims of the skeptics do not undermine the assertion that human-made climate change is already happening and is a serious long term threat. Indeed, the recent publication of the State of the Climate by the US National Oceanic and Atmospheric Administration (NOAA), analyzing over thirty indicators, or climate variables, concludes that the Earth is warming and that the past decade was the warmest on record. Quantifying cause and effect or projecting future conditions is always incomplete in a system as complex as Earth’s Climate; claims where multiple factors impact the observations. Conclusions are thus presented in terms of probabilities rather than dead certainties. This uncertainty is not always adequately explained in the public debate and, when discussed, can appear to be a challenge to the credibility of the field. However, uncertainty is an inevitable component in our understanding of any system for which perfect knowledge is unattainable, be it markets or climate.

    To us, the most persuasive argument in support of climate change is that basic laws of physics dictate that increasing carbon dioxide levels in the earth’s atmosphere produce warming. (This will be the case irrespective of other climate events.) The only way that warming can be mitigated by natural processes is if there are countervailing ‘feedback mechanisms’, such as cooling from increased cloud cover caused by the changing climate. A key finding of the current research is that there has so far been no evidence of such countervailing factors. In fact, most observed and anticipated feedback mechanisms are actually working to amplify the warming process, not reduce it.

    Simply put, the science shows us that climate change due to emissions of greenhouse gases is a serious problem. Furthermore, due to the persistence of carbon dioxide in the atmosphere and the lag in response of the climate system, there is a very high probability that we are already heading towards a future where warming will persist for thousands of years. Failure to insure against that high probability does seem a gamble worth taking.

  4. Allen C says:

    Gee, this is in direct contridiction with the findings of the Norwegian Geological Society (http://www.ngu.no/en-gb/Aktuelt/2008/Less-ice-in-the-Arctic-Ocean-6000-7000-years-ago/). One has to wonder which study is right

  5. Doug Bostrom says:

    Allen, your link is broken.

    Forced to guess, I’d have to put my “better” vote on the analysis supported by more data.

  6. David says:

    NOAA released their US State of the Climate reports for the month of August: 7th warmest August on record for the continental US; 4th warmest summer.


  7. PurpleOzone says:

    S. F. Singer stated flatly in his book that further melting of the Arctic ice would not occur. He wrote that ~ 2004.

    In spite of his error he’s still running around the world spreading his truthiness. Today he’s in India

  8. Steve Bloom says:

    Fixed link to page describing Norwegian study. Allen C. might consider reading it. There’s no contradiction.

  9. David says:

    Steve #8,

    Yeah, it looks like that study only focused on the area north of Greenland. Plus, that study was released in October 2008, whereas the one Joe cites was from July 2010. So, the more recent study may have had new or better data.

  10. Doctor Gee says:

    I’m a bit late to the game here, perhaps, but what evidence do we have that orbital fluctuations today are markedly different from those 10,000 years ago? Is it radius differences attributable to ice sheets from the last glacial period, predictable variations in the earth’s rotational tilt, some combination of these two or something completely different?

  11. Steve Bloom says:

    Re #10: Search in Wikipedia for Milankovitch, Dr. Gee. In short, there are three different kinds of orbital change that combine to affect climate. Astronomers have long been able to calculate these changes with precision, which is how astronomer Milankovitch was able to come up with his idea of orbitally-timed glacial cycles decades before the paleoclimatic evidence was available to prove him correct.

  12. Steve Bloom says:

    Here’s a public copy of the Polyak et al. paper.

    I looked for a reference to the Norwegian study, but there wasn’t one because (and I confirmed this using Google Scholar) nothing ever got published. Possibly the data was not what it seemd to be at first glance. In any case, I’ll email the principal scientist and ask her what happened. It’s also possible the Polyak paper discusses the information somewhere. Finally, while I’m no expert, based on recent melt patterns Independence Fjord is one the wrong side of Greenland to be a candidate location for the last sea ice to melt, which would make wave action there a poor proxy for an ice-free Arctic.

  13. Doctor Gee @10: The conclusions relating to AGW do not depend upon a single line of evidence or reasoning, a point which is common to all scientifically valid forms of inquiry. There is a vast constellation of not simply individual atoms of facts, but entire relational structures of evidence and logic that independently determine matters like orbital distance, tilt, solar irradicance, etc, do not account for the contemporary observations.

    In no small part, this is because these same constellations of structures have so thoroughly filled in the picture of previous climate change events. This is not to say that the fine points of past changes are all so well understood. Rather, the gross points of past changes are so grossly absent now that we don’t need to consider those fine points in order to reject the natural causes of the past as operating in our present.

    So the shorter answer to your question is, “No. It is not ‘this’ OR ‘that.’ It is ‘this’ AND ‘that’ AND ‘all of the above’” that excludes natural causes as the proximate reasons for this immediate set of events. In addition to many other positive lines of evidence (the unequivocally human origin of the current increases in CO2, e.g.) attributing the current observations to anthropogenic causes is extremely well-founded.

    (I realize that this is a painfully generic answer to a question that calls for specifics. The specifics are so much better presented here and at other sources (also recommended here) that I content myself with doing nothing more than offering a skeleton that better qualified persons have already fleshed out.)

  14. Neven says:

    Thanks, Joe. I really learned a lot from this very useful post.

  15. Steve Bloom says:

    Gary and Dr. Gee, the best place to start for the paleoclimate big picture is with Richard Alley’s recent AGU presentation. Richard is second author on the Polyak et al. paper.

  16. Steve Bloom says:

    Wow, everyone should look at this amazing animation of the UniBremen concentration graphic from 8/26 through 9/7 (from Jack Taylor by way of Neven’s sea ice blog). It shows in a way that words and stills can’t how thin and mobile the ice is, and how rapidly so much of it is being shoved out the Fram Strait to its doom even while extensive melting (for this time of year) continues in other areas. For those unfamiliar with it, the dipole anomaly (details on it here) is a new weather pattern driven by the warming Arctic, and is responsible for the 2007 sea ice record low and the sharp drop earlier this summer.

    (This is trying again with a revised version of a comment that seems to have been eaten by the software.)

  17. Michael says:

    I’m surprised that there hasn’t been any mention of this study, which I think is major, since it suggests that even if we stabilized CO2 levels right now, with little additional increase, there would still be a very large Arctic warming – with BAU, throw in another 20 degrees F of warming:

    Arctic Climate May Be More Sensitive to Warming Than Thought, Says New Study

    “Led by the University of Colorado at Boulder, the international study indicated that while the mean annual temperature on Ellesmere Island in the High Arctic during the Pliocene Epoch 2.6 to 5.3 million years ago was about 34 degrees Fahrenheit, or 19 degrees Celsius, warmer than today, CO2 levels were only slightly higher than present.

    “Our findings indicate that CO2 levels of approximately 400 parts per million are sufficient to produce mean annual temperatures in the High Arctic of approximately 0 degrees Celsius (32 degrees F),” Ballantyne said. “As temperatures approach 0 degrees Celsius, it becomes exceedingly difficult to maintain permanent sea and glacial ice in the Arctic. Thus current levels of CO2 in the atmosphere of approximately 390 parts per million may be approaching a tipping point for irreversible ice-free conditions in the Arctic.”"

  18. Steve Bloom says:

    I’m sure Joe blogged that, Michael. Unfortunately it’s just one of many Pliocene-related papers that point toward very bad news. Now if we’re very, very lucky, transient climate sensivitity is low enough that we’ll have time to at least mitigate some of the consequences. If not, we have condemned our collective descendants to some interesting times or, as Joe puts it, hell and high water. At this point the latter seems far more likely, I’m afraid.

  19. Steve Bloom says:

    Sorry, although that was probably obvious, I didn’t make it clear in my next-to-last comment (still in moderation due to links) that the dipole anomaly is also responsible for the present loss.

  20. Neven says:

    More on the fate of the Arctic Dipole Anomaly and some graphs and statistics in my latest Sea Ice Extent update. 2010 has dived under the 5 million mark.

  21. JeandeBegles says:

    Joe thank you for this very interesting post with a lot of new details very well explained and documented. One of them is disturbing for me; it seems likely that past warming (12 000 years ago, 125 000 ou 450 000 years ago) were stronger than today. I wonder what happened then to the permafrost. My question is that if the permafrost starts its melting it triggers a very powerfull and catastrophic positive feed back that I understood is a quite sure tipping point.
    My question is did this tipping point occured in the recent past (less than 1 million years ago). I think Not. If not, why?

  22. perceptiventity says:

    How likely is it that the Arctic is now only responding to the 1980′s CO2 ?

  23. BBHY says:


    Natural carbon sources and carbon sinks are in equilibrium. When the climate warms slowly, and carbon sources gradually increase, the carbon sinks have time to react and maintain that equilibrium.

    What is happening now is that we are increasing carbon at a highly accelerated rate, and it takes time for the sinks to adapt, so they are not keeping up.

    It’s like when you get an inch of rain in a day it makes the grass grow, but 200 inches of rain in a day is a huge flood and washes your house away. The system can only handle so much at a time. Too much, too fast overwhelms the natural system.

  24. David Ferrell says:

    JeandeBegles’ question (in comment #22) might be answered in short or long form, but one way to put it is to say that the past episodes of warmer temperature to which he refers (12,000, 125,000, and 450,000 years ago) were EQUILIBRIUM warmings that happened as a consequence of weak (i.e., very small) forcings applied over many thousands of years due to slow changes in high-latitude insolation (these in turn being secondary to changes in the tilt and precession of the earth’s axis of rotation), and cannot be directly compared with today’s out-of-equilibrium climatic situation. Because of the recent rapid rise in greenhouse gases, Earth is currently far out of energy balance; a mean whole-Earth net positive forcing of some 500 trillion watts (corresponding to roughly one megawatt of excess heating for every square kilometer of earth’s land and ocean surface—0.9 to 1.0 W/m^2) is now being applied, with climatic equilibrium lying in the indefinite future.

    This represents a huge global energy imbalance, since in just one short diurnal period of 60 sec/min x 60 min/hr x 24 hr/day = 86,400 seconds, that 500 trillion watts of continuously applied power adds up to more than four times ten to the nineteenth (40000000000000000000) joules of energy, in the form of greenhouse-trapped terrestrial waste heat. That’s about equal to the energy that would be released by detonating all the warheads and bombs in the world’s nuclear arsenals today, which number in the tens of thousands. The largest earthquakes release about as much energy, as do superenergetic ENSO events.

    Climatic heat sinks (oceans and ice sheets) are absorbing this massive blow, which over a period of 25 years adds up to energy of world altering magnitude, on the scale of the 10^8-megaton yield of the asteroid impact believed responsible for the dinosaur extinction 65 million years ago. This is comparable to the sun’s energy output to the entire universe over one millisecond, about four times ten to the twenty-third (400000000000000000000000) joules. (The total solar luminosity is ~4 x 10^26 watts, which over 0.001 second equals ~4 x 10^23 joules of radiant energy.)

    Today’s cumulative global warming, in other words, considered on the time-scale of a quarter century, is astronomically large, the energetic equivalent of a slowly-impacting asteroid—more or less like the end of the world happening in slow motion. As Newton pointed out, every action has an equal and opposite reaction, and the climate system is just now starting to react to the blow we have so far delivered. All the Hell and High Water starting to break loose in the forms of extreme climate and weather events around the world is just the leading edge of a colossal wave of change starting to sweep over the earth.

    Call it a tsunami of global change.

    By contrast, the equilibrium warmings 12,000, 125,000, and 425,000 years ago were very mild and reflected a situation where the all the feedbacks (including the long-term or so-called “slow” feedbacks connected with reduced ice albedo, CO2 release due to warming and flushing out of the deep oceans, and methane releases) had come into play and essentially played themselves out. That takes thousands of years. While the cumulative natural change was large in absolute terms, the change in any given century was typically small, reflecting the relatively small forcing being applied. Correspondingly, the associated feedback-induced changes in ice albedo, atmospheric CO2, and methane were extremely modest compared to the destabilizing changes we’ve got coming today. Methane release due to climatic warming is potentially catastrophic only where the warming, like today’s, is of very large magnitude.

    The inertia of the climate system has so far mostly insulated us from the blow delivered by man-made greenhouse gases, which we’re just starting to wake up to now and won’t fully comprehend until it is slamming us with something approximating full force. Then our societies may simply disintegrate under the impact—but slowly in comparison with what would happen if an actual asteroid were to impact the planet tomorrow. Our destruction may therefore take some time, perhaps a century or more. Our immediate descendants and their children will find out.

    Most experts nevertheless believe there is still time, just barely, to deflect the worst of the blow by mounting a World-War II-scale effort to get ourselves off a diet of fossil fuels by about (say) 2030 at the latest—beginning right now with deep cuts in global carbon emissions. We can do it if we make it the very highest priority and go into a no-holds-barred, crash-program mode, but the window of opportunity for it will soon close.

  25. KC says:

    A draft of this article was published as a US CCSP product – available at http://www.climatescience.gov/Library/sap/sap1-2/public-review-draft/sap1-2-prd-ch8.pdf

  26. JeandeBegles says:

    Thank you BBHY for the quick answer, and thank you David Ferrell for the impressive answer. Now I got it: it is the equilibrium in the past and the today inbalance that will make the great difference.
    The urgency to act and cut our CO2 emissions is obvious. But in contrast the passivity, the denial of the bad news, the habit to dig our head in the sand, the public distrust for their government, all this let us stalled in the business as usual.
    A small, and may be futile, way to awake people could be to stop talking about CO2 tons (who ever dealt in his life with ton of wathever, and specially of gas ?) and start talking of carbon kilo (equivalent to the burning of 1 litre of oil:
    If you want to improve your french: http://taca.asso-web.com/29+un-kg-de-carbone-svp.html )
    Everybody can understand his personnal impact in the ghg emissions.
    Thank you for your remarks.

  27. J Bowers says:

    Re. 18 Michael
    One of the authors, David Greenwood, had this to say at Climatesight…

    “The implication of our research is that we may already have passed a tipping point for major increases in Arctic temperatures due to increasing levels of atmospheric CO2. Our research is based on a fossil site on Ellesmere Island that shows Boreal forests (like those that span most of northern Canada south of the tree-line, and also Russia and Alaska and Scandanavia) were present, including larch, poplars, white cedar, and animals such as beavers, bears, deer, etc.”


  28. NeilT says:

    The problem with communicating the issue has nothing to do with tons of CO2 or carbon Kilos. For the average man in the street is comes down to “How screwed you are today”.

    You just have to look at serious “at risk” hurricane areas to work out how the human “herd” psyche works. When an area is flattened by a Cat4/5 hurricane people “get it” and tend to move out. Simultaneously people, over a period of years, move back into the countryside flattened by the last Cat4/5 as they are either unaware, or don’t believe.

    The next time a Cat4/5 roars over the same ground all over again, a whole new generations “gets it” and they start to move out again. The cycle is ever repeating.

    The problem with this kind of short sighted idiocy is that with AGW we only get one chance. Once the climate of the planet is finished with us there won’t be many of us or much of a planet (in human holocene terms), left for the survivors to change location.

    In many ways Al Gore has the rights of it. He’s used to communicating with the common man. His message is simple. “Yes you’re really screwed ‘right the hell now’”

    Apologies for the language, but it really is difficult to get it over any other way.

  29. Mike Lizzi says:

    I am a believer in human caused climate change. But this article is another distortion of facts on which the deniers will feast.

    The authors being quoted are saying there has been no time in the recent geologic past when the Arctic was ice free in the Summer. We are not there yet. Your title is “jumping the gun”. Scientists currently have no way to guage the past extent of Summer ice beyond “a lot of ice”, “little ice” and “no ice”. And there have been conditions of “little ice” in the recent past. The Norwegian study talks about such a period some 7,000 years ago. So, until we get to “no ice” we only have the right to say we have not experienced these conditions for 7,000 years.

    [JR: The author of this comment has apologized for it here.]

  30. Steve Bloom says:

    Mike, “recent geologic history” in the headline refers to the last few thousand years, as the post makes clear.

  31. villabolo says:

    Michael says:
    September 8, 2010 at 9:08 pm

    Arctic Climate May Be More Sensitive to Warming Than Thought, Says New Study

    “Led by the University of Colorado at Boulder, the international study indicated that while the mean annual temperature on Ellesmere Island in the High Arctic during the Pliocene Epoch 2.6 to 5.3 million years ago was about 34 degrees Fahrenheit, or 19 degrees Celsius, warmer than today, CO2 levels were only slightly higher than present.

    I’m not a professional but I can find one potential flaw with this study. Did they take into account that ocean currents were very different during the Pliocene because continental drift had not yet connected South America with Central America?

    The Isthmus of Panama did not exist, allowing ocean currents from the Gulf of Mexico to go straight into the Pacific. This created an ocean current that redistributed heat differently throughout the Earth. It may have been the reason why the Pliocene would have been warmer than today in spite of having similar CO2 levels.

  32. Eve says:

    David Ferrell – You are saying some pretty serious things about the future of the human species. I understand what you are saying and it makes sense to me that human-caused disequilibrium is different from natural processes, but not being a scientist I cant judge the accuracy of your remarks. Could you tell us what are your credentials?

  33. Mike Lizzi says:

    I think I need to apologize to the author of this blog for my criticism. I did not read the material carefully enough.

    [JR: Ok.]

  34. David Ferrell says:

    I here correct an omission in my post #25 which might be a source of confusion to some readers. When at the conclusion of the third paragraph from the end, I wrote, “…Methane release due to climatic warming is potentially catastrophic only where the warming, like today’s, is of very large magnitude,” I should have said, “…Methane release due to climatic warming is potentially catastrophic only where the warming, like today’s, is of very large magnitude RELATIVE TO THE TIME SPAN OVER WHICH IT OCCURS—or in other words where sustained warming occurs that is much more rapid than that typically seen in natural climate changes.” Today’s rapid warming—technically, high RATE of warming—is not to be confused with an equilibrium temperature rise, which ordinarily requires centuries to millennia since slow feedbacks come into play, but is a measure of the current imbalance between incoming (solar) and outgoing (terrestrial) radiation at the top of the atmosphere. It is this imbalance which is adding net energy to climatic sinks thus and driving the global temperature increase. One (the real-time net radiative forcing due to man-made greenhouse gases, expressed as the contemporary warming rate) is the cause; the other (the equilibrium temperature rise after the feedbacks have acted) is the effect.

    Due to the thermal inertia of the climate system at least half a century is necessary for even the climate system’s fast feedbacks to respond to the current imbalance, and thousands of years are necessary for the slow feedbacks to fully respond. So there is a long built-in time-lag between the cause and its effects. The long-term system response typically includes massive CO2 release from warming deep oceans and methane releases from such sources as expanding wetlands and melting permafrost. Only in the far future will the full effects of current and future CO2 increases be reflected in an equilibrium temperature rise as measured by the thermometer, whereas the peak warmth of (say) the early Holocene at ~10 kya shows us a climate already in rough equilibrium, where all the feedbacks have had time to act.

    Thus, despite the interruption of the Younger Dryas beginning around 12.8 kya, the difference between (a) the slow transition from full glacial to early Holocene conditions between about 10,000 and 14,000 years ago and (b) today’s rapid climate change (leading we don’t know where—possibly to total destruction but certainly to massive societal and ecosystem disruption) is approximately the difference between lowering oneself onto a comfortable mattress and falling off a cliff.

    Comparison of today’s rapid anthropogenic warming with the equilibrium warmth at 10, 125, or 450 kya is therefore tricky and potentially misleading, like comparing apples and oranges. Deniers (who don’t really understand this) constantly employ such comparisons to mislead. To use a metaphor, the peak warmth of the Holocene around 9.5 to 10 kya (the so-called Climatic Optimum) was a sunny ripe orange fit to be enjoyed by the inhabitants of that time, whereas today’s virtually instantaneous warm-up—instantaneous on a geologic time-scale—is a poisoned apple which if fully eaten will cause much sorrow and anguish for inhabitants of our present Earth, tearing asunder not only countless lives but the very fabric of life itself. Many of us in the rich world, relaxing in our saunas and heated swimming pools, enjoying our energy-intensive lifestyles, driving our gas-guzzling SUVs, and chilling out in air-conditioned comfort, are eating poisoned fruit. Meanwhile, under the delusion that this wasteful, overconsumptive lifestyle can continue indefinitely, we simply tune out the increasingly urgent warnings of the expert climate-science community that our carbon-hungry lifestyles cannot be sustained and that unless we reform ourselves quickly we are probably doomed. The rapid rise in CO2 and other greenhouses gases has delivered a massive jolt to the climate system, whose full effects will unfold over a time span of a hundred generations or more, but with devastating effects likely being felt within decades—well within the expected lifetime of many if not most of those alive today.

    The comparison of today’s Earth warming with a world-annihilating asteroid impact happening in slow motion is thus accurate, especially as the energies involved are comparable. The asteroid strike that wiped out the dinosaurs 65 million years ago very suddenly released about as much energy—estimated at one hundred million equivalent TNT megatons (one megaton of TNT releasing some four billion megajoules and requiring a freight train 300 miles [480 km] long to carry it)—as will be added to the climate system between now and 2035 by man-made greenhouse gases. This is at the current Earth-warming rate of ~500 million megajoules per second, which scales with the total heat generated over time by an unending string of hydrogen-bomb detonations of 0.125-megaton yield going off at the rate of one per second. But the warming rate is increasing. The total global mean historical forcing since 1750 is now approaching 2 megawatts per square kilometer, about equal to a 1% increase in solar brightness. About half of that corresponds to the existing imbalance between incoming (solar) and outgoing (terrestrial) radiation at the top of the atmosphere. It is as though we had added an extra slice of solar fire to the sun, a slice which is growing larger with time and doing it faster and faster—pitching us onto the dangerous curve known as “accelerating global warming.”

    BBHY’s answer in post #24 to JeandeBegles’ post (#22) was, by the way, excellent, conveying much key information in just a few words through the use of sharp metaphor. Due to my Post #25 having been dashed off rather quickly and submitted in unedited form without fact-checking, the dates I gave for past interglacial peaks diverge somewhat from the correct numbers, which are corrected above. I will answer Eve’s post (comment #33) as soon as possible.

  35. David Ferrell says:

    On September 10, 2010 at 2:56 am Eve (comment #33, in reference to my comment #25) wrote:

    “David Ferrell – You are saying some pretty serious things about the future of the human species. I understand what you are saying and it makes sense to me that human-caused disequilibrium is different from natural processes, but not being a scientist I cant judge the accuracy of your remarks. Could you tell us what are your credentials?”

    I’ll be more than happy to. It’s common for those who make strong statements about global warming to have their credentials challenged, especially if the statements contain information that seems to disturb people, perhaps in part because there’s so much deliberately misleading information out there. No less a one than Joseph Romm—the tireless operator of this highly-regarded website—some days ago had his own credentials challenged by a commentator (whom I politely dressed down in a post of my own since the challenge was patently absurd). You’re doubtless aware that it has become fashionable to question the reliability even of climate scientists themselves. Attempts are made to discredit and smear the profession as a whole, dismissing all of “anthropogenic climate change science” as a hoax or scam. As far as “credentials” go these days, it seems you’re damned if you’ve got them and damned if you haven’t—they “ain’t what they used to be,” as we say.

    I am therefore tempted to ask: does your question about “credentials” imply that if you found out I was a climate scientist—even a famous one like Michael Mann, Kevin Trenberth, or Gavin Schmidt, for example—you would for that reason take me more seriously than if I confessed to being just an ordinary Dave or Al, somebody like Joe the Plumber before he accidentally tripped over into his paltry fifteen minutes of fame?

    Not likely. A number of today’s top climate scientists are as infamous as famous, reportedly marked for criminal investigation (ostensibly for falsifying data) if Republicans gain control of the U.S. Senate this November, since Senator James Inhofe (R-Nebraska) will chair the relevant committee. It doesn’t matter that they’re innocent; a witch hunt is in progress in the land. So it’s actually a good thing that I’m not anybody that the Denialosphere has yet gotten worked up about.

    I therefore and without discomfiture declare myself free of any ties to the suspect profession: I am not a rocket scientist, computer scientist, or climate scientist any more than Al Gore or Bill McKibben are—people who are nevertheless considered (in the RealitySphere, that is) reliable sources of information about climate, because they pay close attention to what the science says.

    I did say some “pretty serious things about the future of the human species,” as you say, but anybody who really “gets it” (in James Hansen’s sense—in his book Storms of My Grandchildren) is ethically obligated to do that. Mine was a statement about the potential future, thus conditional as all such statements necessarily are. Actually, my estimation of the likelihood of catastrophic future warming under a “business-as-usual” scenario is not substantially different from that of Hansen or the rest of the scientific mainstream today, including such authorities as John Holdren (the White House science advisor) and Romm himself, who writes daily blogs here and has a PhD in physics from MIT. The words “catastrophe” and “catastrophic” frequently appear on this site in reference to future warming, in Romm’s own writing and in the comment sections themselves, which many people who are actual scientists read and contribute to.

    Comments on this site are carefully moderated, by the way, which means that while foolish people are allowed to appear as foolish as they are up to a point, deliberate attempts to fool or mislead the public, to post inaccurate or misleading information, to poison the discussion by engaging in anti-science diatribe, or to run characteristic denier scams (ArcticIceHealthy.exe, AGWDead.run, Don’tExhaleCO2.ridicule, PolarBearsFine.cuddle, etc.) are not allowed to stand.

    That provides reasonable assurance that the information in my post, much of it quantitative and easily fact-checked, is free of obvious or gross scientific inaccuracies, as these would be flagged by the moderator. Any serious distortion would soon be jumped on by CP’s alert readers, many of whom are also regulars at RealClimate, where commentators help to police the blog and Gavin Schmidt absolutely won’t tolerate stuff that is made up. Falsification, anti-science screed, garbage, bunkum, BS, and other unseemly productions of the Denialosphere are out. People who make honest mistakes are corrected, but dishonest ones who post nonsense risk embarrassment or are advised to find another pasture to dump their CowS**t on.

    Making realistic projections about the future of Earth’s climate is not a matter of guesswork, wishful thinking, or gazing into a crystal ball. All relevant information—peer-reviewed scientific reports, agreed-upon facts, observations, the results of modeling experiments, and obvious long-term trends—must be integrated into a credible “Big Picture” of warming that suggests what the trajectory of future climate change is likely to be, especially if humanity stays on its present course of unrestrained fossil-fuel emissions. Links to the necessary information are available from many sources including the ClimateProgress and RealClimate websites; with that, forming an accurate picture requires few tools beyond an application of ordinary logic.

    That’s another way of saying that 2+2=4 no matter who does the addition, and that gravity works whether or not Isaac Newton says so. You don’t have to be a climate scientist. It’s imperative that we get ourselves free of the craven hunger for authorities to tell us what’s what and do our thinking for us. If we can’t think for ourselves, then we have absolutely no way of knowing who is a real “expert” and who isn’t, making us easily fooled by any smooth talker who tells us what we want to hear while putting on an act of being The Great Authority, like The Viscount Monckton of Benchley, alias Lord Monckton.

    Nevertheless, people from diverse backgrounds today who are not scientists but who think for themselves and have actually followed the science behind the global warming scenario tend to be in agreement that if we if we continue on our merry way with “business as usual” we’re likely headed for multiple catastrophes not far down the line—severe ocean acidification and warming, devastating phytoplankton declines, the destruction of most life in the seas, climatic extremes far beyond anything in human experience, and the drought-driven incineration of the world’s croplands and breadbaskets. Add to that the eventual collapse of our societies, the rendering of major portions of the earth’s surface uninhabitable, and hundreds of millions or billions dead this century from social unrest, war, dislocation, mass migration, disease, famine, and starvation….

    (Due to considerations of length, the conclusion of this commentary is separately posted below.)

  36. David Ferrell says:

    …Thus, if my statement about what the future holds seems more palpably physical and alarming (“blockbusting”) than most people are used to, this was because I was using a quantitative approach to “communicating climate” that (as I like to say) “delivers the megatons—the information bomb—about what Earth warming really is.” Yes, it really is true that over a time span of just twenty-four hours, the contemporary real-time net positive forcing of about one megawatt per square kilometer (the same as a mean global warming rate of one megajoule per square kilometer per second) adds the heat equivalent of almost one million Hiroshima-sized atomic bombs to the global climatic system; and that over the span of about two decades the accumulated heat approaches the world-annihilating energy of the prehistoric K-T impact—the asteroid strike that wiped out the dinosaurs and most other life on Earth 65 million years ago.

    And in fact, over just one year the added heat comes to about 1.6 times ten to the twenty-second (16000000000000000000000) watt-seconds (joules), the heat equivalent of 4000 gigatons of TNT and about the impact energy of a solar system asteroid 20 cubic kilometers in size (diameter 3.4 km, mass 60 gigatons at typical asteroid density of 3 grams/cubic centimeter). [This figure is arrived at by scaling down ~10 km-diameter asteroid responsible for the dinosaur extinction, estimated to have released the equivalent of one hundred million megatons (100,000 gigatons) of TNT. An asteroid of diameter 3.4 km thus releases about 4% of the K-T impact energy.]

    We’re talking, of course, about thermodynamically degraded energy—“the invisible fire in the greenhouse”—which unlike asteroid impacts and nuclear explosions is largely unavailable for moving things around (doing what thermodynamicists call “work”) but which is nevertheless capable of causing Hell-on-Earth, as by warming the atmosphere and oceans, melting polar ice, raising the global specific humidity, intensifying droughts, and triggering massive wildfires. The fraction of that energy which eventually does become available for work (due to differentially stronger heat-trapping at tropical and subtropical latitudes) is particularly damaging, as by boosting the power of storms and consequent flooding. Thus arises the climate-change syndrome of “HELL AND HIGH WATER” that Joseph Romm has made justly famous.

    If some of us don’t (yet) much notice the effects of the global GHG rise—at least not to the extent that it’s continually hitting us in the face—that’s because the continuous power level (per unit area of the earth’s surface) is low, and the associated energy is mostly not retained by the land surface or overlying atmosphere due to their relative lack of heat capacity. Because the climate system tends toward internal equilibrium, there is a continuous flux of this excess atmospheric energy, as radiant heat, into primarily the oceans, which cover almost three-fourths of the planetary surface. The excess energy trapped by the added greenhouse gases becomes part of the climate system’s internal energy, over time radically unbalancing the earth’s heat budget and bringing on a different type of climate. Because of the strength of the GHG forcing relative to the weak, primarily orbital forcing responsible for climate changes during the past million years, that “different type of climate” is likely to be well beyond the range of the glacial-interglacial climate states in which humans evolved and alien to the equable Holocene conditions which gave rise to civilization over the past 10 kyr.

    To the extent that they can truly compass it, people seem genuinely disturbed by this information, saying they had no idea that the global-warming energy was of such magnitude, steadily but silently building up in the system over the years until—inevitably—it pushes the planet past thresholds that must not be crossed if we are to maintain a livable climate. It is not as though we could geo-engineer ourselves out of the resulting crisis, for once global climate change of this magnitude is set in motion the momentum of the process (system inertia) works against rather than for us. Stopping the process might prove as impossible as for someone to stop a runaway freight train by pushing against it.

    Such a quantitative thermodynamic approach to communicating the reality of Earth warming, employing a yardstick whose units range from the heat equivalent of the combined nuclear arsenals of the world to the world-shattering energies of the largest impacting asteroids, but which fully accords with the facts as we know them scientifically, helps people to grasp what is beyond doubt the most important single fact there is to know about greenhouse-driven Earth warming—that this is not a matter of a few degrees of air temperature change (weather, in other words, which continually fluctuates), but of cumulatively loading the Earth-atmosphere system’s thermal sinks (oceans and ice sheets) with excess energy that, summed over time, is truly of world-altering magnitude, capable of waking the planet out of its million-year slumber of the ice ages and turning it into a different and much hotter kind of place, with consequences that may well include the collapse of civilization and the transformation of Earth into an abode inhospitable to our form of life.

    For today’s anthropogenic climate modification is nothing like the natural climate changes of the past. The human addition of GHGs to the atmosphere is unsustainable. If the current radiative forcing of the climate were continued indefinitely, it would render the planet uninhabitable—finally boiling the oceans and ending all life. People well-versed in this subject are going to have to lay the numbers on the line and do some tough talking to the world at large. Who are those people going to be?