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Comments 121901 to 121950:

121901. JMurphy at 02:26 AM on 25 March 2010
        Is the science settled?
        Oh, and ProfMandia has just reminded me of another so-called 'skeptic' fallacy, recently re-posted : tackling AGW will 'trash the world's economy'. Usually followed-up by : 'The poor (who I am very concerned about indeed) will be the ones most affected. Is that what you want : cos that's what you'll get.'
121902. oracle2world at 02:23 AM on 25 March 2010
        Is the science settled?
        #8 That paper was very interesting. Appears to be peer-reviewed to boot. Focuses on general circulation models, uncertainty, and "parameters" which I keep reading about. When something isn't understood, a parameter is used, that of course supports the conclusion desired.
121903. JMurphy at 02:22 AM on 25 March 2010
        Is the science settled?
        So-called 'skeptics' also like to use the 'argument' : 'See, the science isn't settled, despite what you and your scientists say !' When asked to point out who actually says that, the response is usually along the lines of 'Fat Al Gore said it, to boost his fortune'. Or something like that. When asked to actually prove it, all I have ever seen is a report about Al Gore giving evidence before some US Committee, where the reporter writes that that is what Al Gore has stated. Nothing definite or proven, but more than adequate for denial purposes.
121904. ProfMandia at 02:17 AM on 25 March 2010
        Is the science settled?
        oracle2world states that addressing AGW will trash the world's economy. Hardly. Not addressing AGW will CERTAINLY trash the world's economy. Please see: The Copenhagen That Matters by Thomas L. Friedman in the NY Times. An excerpt: Although it still generates the majority of its electricity from coal, since 1990, Denmark has reduced its greenhouse gas emissions by 14 percent. Over the same time frame, Danish energy consumption has stayed constant and Denmark’s gross domestic product has grown by more than 40 percent. Denmark is the most energy efficient country in the E.U.; due to carbon pricing, through energy taxes, carbon taxes, the ‘cap and trade’ system, strict building codes and energy labeling programs. Renewable resources currently supply almost 30 percent of Denmark’s electricity. Wind power is the largest source of renewable electricity, followed by biomass. … Today, Copenhagen puts only 3 percent of its waste into landfills and incinerates 39 percent to generate electricity for thousands of households. Cap and trade has also worked in the US with regard to sulfur dioxide (SO2) emissions. SO2 emissions lead to acid rain and during the 1980s, acid rain was devastating lakes and forests in the east. In 1988, Congress passed a cap and trade scheme to reduce these emissions by 50%. By 2004, regulated polluters reduced their emissions by 40% more than required! The Dept. of Energy estimates that the cost to limit emissions ended up being a mere 0.6 percent of the polluters operating expenses. When CFCs were to be regulated/banned, there were similar claims of economic hardship. Like the other claims, these have not panned out. I also point you to: How to Talk to a Conservative about Climate Change which addresses costly consequences to a "do-nothing" approach to AGW.
121905. Berényi Péter at 02:16 AM on 25 March 2010
        Is the science settled?
        You have left out black carbon (soot), which is a very effective agent in melting snow, even in the absence of any warming. Of course, it can increase temperatures as well by decreasing surface albedo in snowy regions, hence increasing ASR (Absorbed Shortwave Radiation). Early 20th century warming of the North Atlantic region is due to this soot effect. Even now soot from American industry and wildfires is deposited on Greenland snow en masse. It is also the kind of pollution that can easily be mitigated, with immediate local benefits. On the other hand, regarding CO₂ you have only demonstrated two points beyond any reasonable doubt.
        1. Atmospheric carbon dioxide level is increasing
        2. CO₂ does absorb (and emit) IR radiation at certain wavelengths
        It is a far cry from demonstrating it makes Earth warmer indeed.
121906. Ian Forrester at 01:54 AM on 25 March 2010
        Visual depictions of Sea Level Rise
        New Moore Island is now No More Island. Disputed Bay of Bengal island 'vanishes' say scientists
121907. oracle2world at 01:52 AM on 25 March 2010
        Is the science settled?
        Dear #9 ... and what about the Duke rape case? The prosecutor indeed covered up information that exonerated the defendents. Academics signed a letter piling on without a second thought. And for what? The academics had nothing riding on the outcome of the case. The prosecutor had won his election, he could have released the evidence, ended the case, and moved on. The OJ case was circumstantial, which is ALWAYS a difficult case to try. The cop committed perjury on the witness stand. The glove doesn't fit, and DNA tests in other jurisdictions have been falsified. The standard was reasonable doubt. Monday morning quarterbacks thought the standard had been reached, the jury didn't. That is our system of justice. Even if the simpliest explanation is that OJ was the doer. To push your rope analogy, imagine a rope with a lot of fuzz, like yarn. It looks thick, but the fuzz makes it difficult to determine how strong it is. It could be a piece of yarn, or a piece of steel wire inside. AGW assumes inside the fuzz is something, others say no one knows, not enough to trash the world's economy.
121908. chris at 01:33 AM on 25 March 2010
        A peer-reviewed response to McLean's El Nino paper
        re HR 18:11; 24 March, 2010 Interesting. That clarifies why the editor(s) chose not to publish the McL et al response to Foster et al's comment. McL simply didn't address the points raised by Foster et al. In fact the McL response reinforces the fallacies of their original paper that Foster et al highlight, since they admit that the large apparent contributions of ENSO to variance in the temperature records (72% of variance in MSU atmospheric temperature; 68% of variance in RATPAC radisonde atmospheric temperature), doesn't actually apply to these variances at all, but to the smoothed and derivatized data.... ...which is obvious and exactly the point that Foster et al made, and having admitted that, there isn't really anyrhing left of substance to their paper that differs from previous analyses. ...and of course, McL et al didn't address Foster et al's critique of the non-sequiter of McL et al that "mean global tropospheric temperature has for the last 50 years fallen and risen in close accord with the SOI of 5–7 months earlier shows the potential of natural forcing mechanisms to account for most of the temperature variation." [Note that McL et al reintroduce a similar but rather more blatant non-sequiter in the abstract of their blog response, and that in itself should render their response unpublishable, at least in that form.] There isn't really the "right of reply" that McL consider they were denied in their blog pamphlet you linked to. Editors would certainly be expected to invite a rsponse to a comment on their paper. But this response should conform to basic scientific standards, the foremost in these circumstances being that it should address the points in the comment. McL et al. didn't do that, but chose to restate the erroneous points in their paper, assert their correctness and to bluster instead. All this doesn't matter from a scientific point of view. We're pretty much back where we always knew we were, various bits of people's time having been wasted. I suspect McL et al consider they've done a pretty good job altogether....
121909. tobyjoyce at 01:27 AM on 25 March 2010
        Is the science settled?
        Your characterisation of science puts me in mind of a recent book on the OJ Simpson trial by Vincent Buglosi, who prosecuted Charles Manson in the 1960s. OJ Simpson, almost everyone now agrees, was guilty of murdering his ex-wife and her lover. There was blood evidence, he fled when the cops tried to arrest him, he had a history of violence etc. Yet his defence team persuaded the jury of three simple propositions: - There was a chain of evidence which had to be strong at every link. - Any broken link destroys the chain, and therefore the whole case ("If the gloves don't fit, you must acquit"). - The chain was tainted by an irredeemably racist cop, and you could never be sure that the cop had not "fitted up" all the other evidence. This is similar to the case against AGW - ALL the evidence must be beyond doubt, a single contrary piece of evidence "falsifies" the AGW case, "corrupt" scientists cannot be trusted ("Climategate"). Bugliosi counters with another metaphor - the evidence is not a chain but a rope of many fibres. Some fibres may be weak, and even fail. But overall, it the combined strength of the fibres that make the case. One "falsification" does not destroy a case or a science - usually that fibre can be repaired. A jury may discount a single piece of contrary evidence if the remainder of the evidence is sufficiently strong (in their estimation). The can still make a decision "beyond reasonable doubt". Bugliosi's view is close to the science philosopher's view of science - only when evidence against a theory begins to accumulate (several fibres start to break) will scientists contemplate a new or alternative theory. These are what Thomas Kuhn called "paradigm shifts". Climate science has a pretty strong bundle of fibres comprising the evidence, which you set out here. The AGW paradigm is paramount in climate science, but of course is never 100% beyond doubt.
121910. gallopingcamel at 01:27 AM on 25 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        David Horton (#37), It seems that I am irritating you and that is not my intention. In an effort to set up a more cordial exchange of views, my favorite adjective for greenies is "well-intentioned". Furthermore I support the idea of reducing CO2 emissions drastically and soon. However, this blog is not into "solutions" as yet. My points thus far have been that the MVP affected the Greenland ice sheet and to suggest that expanding glaciers have mostly negative consequences from a human perspective. I have tried to cite sources such as Wikipedia that you will not dismiss without reading. I don't understand your sarcastic tone while mentioning the efforts by monks to exorcise advancing Swiss glaciers. It is well documented and in at least one case it seemed to work. As John Cook mentions (#36) this is an amusing anecdote. When (not if) the Laurentide glacier re-establishes itself all the way to New York City it won't be amusing any more. I guess it all depends whose ox is being gored.
121911. Arkadiusz Semczyszak at 01:26 AM on 25 March 2010
        Is the science settled?
        Percentage uncertainty is still too large in relation to the proposed costs (Stern Report). For example, CO2 from the soil (one of the main arguments of skeptics) has the same isotope ratio. The process of decomposition in the soil can not be examined from a satellite. CDIAC soil respiration determined on the basis of a properly working (Interannual variability in global soil Respiration, 1980-94.) Covering Although 14 years of research, but ... "Soil respiration in terrestrial ecosystems worldwide is estimated to be 50-75 Pg C/year (Raich and Schlesinger 1992 ). The carbon cycle in soil has attracted much attention because it accounts for the second largest flux from terrestrial ecosystems, behind gross primary production (100-120 Pg C/year). In comparison, fossil fuel emissions contribute over 5 Pg C/year. [...]"(Duke University - http://www.biology.duke.edu/bio265/ajm21/intro.html). @ jsam "Very cogent and well written." In a well-known magazine "Skeptic" containing treated acute assessment (review) in numerous publications throughout the skeptical science (not just the climate) is the article: http://www.skeptic.com/the_magazine/featured_articles/v14n01_climate_of_belief.html Let me quote just one sentence: "It turns out that uncertainties in the energetic responses of Earth climate systems are more than 10 times larger than the entire energetic effect of increased CO2." Very cogent and well written.?
121912. ProfMandia at 01:26 AM on 25 March 2010
        Is the science settled?
        Ken, Here is what Bony et al. (2006) founbd when reviewing the literature: Water Vapor (1.80 ± 0.18 W/m2/K) Lapse Rate (-0.84 ± 0.26 W/m2/K) Clouds (0.69 ± 0.38 W/m2/K) Surface Albedo (0.26 ± 0.08 W/m2/K) Knutti and Hegerl (2008) and IPCC (2007) conclude that various observations show a climate sensitivity value of about 3oC, with a likely range of about 2 – 4.5oC and that 2C seems pretty well constrained if you throw out Lindzen's work. I will download that Trenberth paper now. Bony, et al. (2006). How well do we understand and evaluate climate change feedback processes? Journal of Climate, 19, 3445 - 3482. Knutti, R. & Hegerl, G. (2008). The equilibrium sensitivity of the earth's temperature to radiation changes. Nature Geoscience, (1), 735 - 743.
121913. jimvj at 01:24 AM on 25 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        John: In #34 you responded: "The more serious impact from disappearing glaciers is the eventual loss of a source of seasonal drinking water for hundreds of millions of people." That point needs to be fleshed out. If AGW reduces the annual snowfall in the glacier regions long term, then not only will the glaciers disappear, but the available water will also decrease. If not, then without glaciers all that snowfall will melt in the spring/summer, potentially causing flooding. To counteract this more dams would have to built. The glaciers act as dams that smooth out the effects of seasonal temperature variations.
121914. Berényi Péter at 01:16 AM on 25 March 2010
        Visual depictions of Sea Level Rise
        Sea level rise relative to what? Consider the following imege pair: The first one is Figure 3 from the post above while the second one is something completely different. Still, the overall pattern is rather similar. How can that be? Well, Geoid Height (undulation) is a tricky concept. GPS satellites provide heights above a reference ellipsoid, usually GRS 80. This ellipsoid is supposed to be a fair overall representation of the shape of Earth in a sense that it would be the closest (least squares) approximation of the actual gravitational equipotential surface defined by average sea level over all the oceans. In reality, this ellipsoid is defined by a standard adopted by the XVII General Assembly of the International Union of Geodesy and Geophysics in 1980. As such, it is a "frozen" approximation. Neither its accuracy is better than that of pre 1980 measurements nor does it follow changes in the shape of Earth. One would think there must be a secular change in the parameters of the best fit reference ellipsoid, glacial rebound alone should produce such an effect. Mantle material deep down is moving poleward, with time making Earth a bit more spherelike. Using a fixed reference surface like GRS80 this effect is ignored. Anyway, we are not interested in sea level change relative to an arbitrary reference surface, but to some equipotential surface instead. On such a surface there are neither ups nor downs, everything is on the same level relative to everything else. If sea level rises relative to it, it should get to a level of higher gravitational potential, i.e. it goes up. As the gravitational acceleration is fairly constant, this potential difference can be measured in milimeters as well. How do we define such a surface? In principle it is simple. It is enough to determine vertical direction above each point on Earth by local gravimetry. The equipotential surface is the one having a normal vector with the same direction as the local vertical at each point. In practice small pathes of an equipotential surface can be constructed this way (useful for e.g. mining operations), but due to undersampling and error accumulation, over longer ranges this method is useless. The problem is that inhomogenities in Earth density have a direct effect on local "vertical" direction, so the real equipotential surface is rather crinkly. As we move up (and get farther from local inhomogenities) the surface tends to get smoothed out. Satellite orbits are only sensitive to low spatial frequency changes in the verical. So. If we fancy the equipotential surface as a sum of spherical harmionic functions, lower order harmonics can be estimated from satellite orbits, higher (more crinkled) ones can not. The result is a surface which is close enough to the actual equipotential surface, althogh its individual normal vectors can differ considerably from the local vertical direction. The shape of the surface having a nominal zero potential, that is the same as average sea level at a particular time (as far as it can be determined) is called the geoid. For practical purposes this shape is not defined by spherical harmonic coefficients, but by geoid heights (also called undulations) relative to the reference ellipsoid. The second map above depicts this representation. Undulations have a fairly large (almost 200 meter) range, many thousand times larger than supposed changes in sea level. They are known with a rather low accuracy as well (estimated errors are sevaral meters). There is no legitimate reason to be a correlation between undulations and local sea level trends. If we do observe one (as we do indeed), it can only be due to a poor job done by Ssalto/Duacs products in separating true sea level trends from other factors. See also Determination of Global Sea Level Rise and its Change with Time by Martin Ekman
121915. oracle2world at 01:16 AM on 25 March 2010
        Is the science settled?
        Well, great article. Finally says aerosols have a lot of uncertainty. And science is never settled. So why don't we just completely discard the "settled" nonsense. However ... "To argue that the 5% that is poorly understood disproves the 95% that is well understood betrays an incorrect understanding of the nature of science." sort of ignores the 5% might be really really important. Doesn't disprove any of the other 95%. This is so common in science there is even a saying, that goes something like "Another Beautiful Theory Slain By An Ugly Fact". People have languished in prison for heinous crimes, convicted by evidence beyond a reasonable doubt, and later exonerated by DNA testing. Maybe 1% of the evidence changed the conclusion. If aerosols are poorly understood, and not modeled by the computer models ... none of this counts for much. The AGW theory of course is that small increases in a rare gas in the atmosphere has far ranging effects. Nothing unusual about a theory where a small amount of something effects big changes (aka catalysts). By the same token, aerosols have an enormous effect - and I don't think that is really under dispute. Volcanic eruptions, SO2 pollution, etc. So if a part of the theory is poorly understood, and not modeled, that can completely change the conclusions ... there is a problem. What they call a Big One. An automobile can have 99.9% of its parts working, proven, "settled", understood, and if a wheel falls off - we still consider it a failure. And let me explain what science is. The "best" theory is considered to be the least long-winded explanation for a dataset. Occam's Razor. We use the model that the earth goes around the sun, not because of any inherent "truth", but because it simplifies the mathematics enormously. The dataset, what dots of light move across the sky when, doesn't change regardless if you use the "universe revolves around the earth' model. The dataset of interest in climate change is temperature. CO2 emissions and increases caused by mankind, while interesting, are not exactly what concerns people per se. So, in line with Occam's Razor, what choices of the least long-winded explanation can be used for avg global temps over time? a. a convoluted theory with CO2 as key variable, that gets more and more convoluted all the time b. temps are within normal variance If b. above, then none of the whining about species disappearing, sea levels rising, etc., etc. matter either. Just one more challenge for life to adapt to, which it has for billions of years. So for anyone using the word "science" ... ask them about Occam's Razor, and if they appear puzzled, figure they are not a scientist. Sort of the "litmus test". Anyone here know what litmus paper is?
121916. chparadise at 01:14 AM on 25 March 2010
        Is the science settled?
        I also like Nature's editorial take on this very topic about a month ago now. They mentioned that there's four areas where the science isn't really settled, and they're by and large dealing with predicted effects of climate change. But, to use the term "the science isn't settled" ends up playing into skeptics hands, when in fact we're using the term in a different manner.
121917. Ken Lambert at 01:13 AM on 25 March 2010
        Is the science settled?
        What you have left out of your discussion John is the effect of net response of the climate system. Dr Trenberth in his AUG09 paper "An Imperative for Climete Change Planning: tracking Earth's global energy" attributes in Fig 4. responses due to Radiative feedback of -2.8W/sq.m and water vapour and ice albedo feedbacks of +2.1W/sq.m giving a net response of -0.7 W/sq.m. This must be added to the net purported anthropogenic radiative forcings of 1.6 W/sq.m which reduces the total net imbalance to +0.9 W/sq.m. There is no direct measurement of these amounts in an atmosphere with an incoming net heat flux of roughly 240W/sq.m. There is also a wide range of uncertainty about the effect of doubling of CO2 to 560ppmv. Increasing surface and tropospheric temperature will raise outgoing longwave radiation (OLR)and some suggest a rise as low as 0.5 degK and others 2-6 degK for this doubling. Such a wide range is an indication that for practical climate change prediction - the claimed well known AG forcings are not much good for such purpose when large unknowns are added and subtracted.
121918. ProfMandia at 00:54 AM on 25 March 2010
        Is the science settled?
        This settles it! :) Just kidding. The Scientific Consensus is my attempt to show why we have enough confidence to take action now. I recently posted on Bart Verheggen's blog the following: I agree that waiting another 30 years will give us more validation but that is comparable to telling a person who we think may have cancer to wait 30 years to see if it kills him. If we are right about AGW, we do not have the luxury of waiting. I wish it were otherwise.
121919. Svatli at 00:53 AM on 25 March 2010
        Is the science settled?
        From an article in The Economist:

        In any complex scientific picture of the world there will be gaps, misperceptions and mistakes. Whether your impression is dominated by the whole or the holes will depend on your attitude to the project at hand. You might say that some see a jigsaw where others see a house of cards. Jigsaw types have in mind an overall picture and are open to bits being taken out, moved around or abandoned should they not fit. Those who see houses of cards think that if any piece is removed, the whole lot falls down. When it comes to climate, academic scientists are jigsaw types, dissenters from their view house-of-cards-ists.

        http://www.economist.com/displayStory.cfm?story_id=15719298
121920. jsam at 00:21 AM on 25 March 2010
        Is the science settled?
        Very cogent and well written.
121921. mspelto at 23:44 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        One point that is not being accurately made in this post is the cause of GIS outlet glacier acceleration "How does it happen? The Greenland and West Antarctic ice sheets sit on bedrock that is underwater. As the oceans warm, they melt the ice sheets from below - this causes the ice sheets to slide faster into the ocean (van den Broeke et al 2009). This is what is being observed now by satellites". --this is not wrong but not correct either. The warm water can only melt the bottom of floating sections of ice tongues. These are very limited in Greenland. The key to acceleration of marine terminating outlet glaciers is to reduce ice thickness at the glacier front. Thinning causes the glacier to be more buoyant, even becoming afloat at the calving front, and is responsive to tidal changes. The reduced friction due to greater buoyancy allows for an increase in velocity. This is akin to letting off the emergency brake a bit. The reduced resistive force at the calving front is then propagated up glacier via longitudinal extension in what R. Thomas calls a backforce reduction (Thomas, 2003 and 2004). The acceleration observed is not primarily due to meltwater acceleration or melting of the floating ice tongue bottoms. These processes maybe happening in some places. It is thinning of the ice tongues that by whatever process that leads to the acceleration. It can be surface melting, it can be basal melting. http://www.realclimate.org/index.php/archives/2008/04/moulins-calving-fronts-and-greenland-outlet-glacier-acceleration/
        Response: Thanks for clarifying my over-simplified explanation.
121922. RSVP at 21:49 PM on 24 March 2010
        The 5 characteristics of scientific denialism
        "JMurphy How is it a 'soft science' ? " Physics is physics. Climate science is "based" on physics (and other hard sciences), and there is nothing within climate science that can be inconsistent with these fundamentals. In order to structure a hard physical model with precision, you need to isolate all significant factors. Global climate is simply too complex to lend itself to this level of determinism. And there is nothing wrong with this fact except for the confusion created by those that cant understand this difference.
121923. Ned at 20:42 PM on 24 March 2010
        Mars is warming
        Actually Sagan, temp measures on other planets could be considered more reliable than some I've seen taken on earth. On Earth we have buoys, drifters, and satellites measuring the temperature of the oceans; met stations and satellites measuring the temperature of the land surface; boreholes measuring temperatures beneath the surface; and satellites and balloons measuring temperatures in the atmosphere. That's orders of magnitude more information than we have about temperatures on any other planet.
121924. HumanityRules at 19:30 PM on 24 March 2010
        Skeptical Science housekeeping: Contradictions, URLs and getting hacked
        Thanks Leo That seems to nail that particular discussion. More evidnce that the simplistic denier/warmer split is of limited use.
121925. warm at 19:03 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        "This reminds me of an story I heard recently - I don't recall the exact details (a google challenge for the curious) but there was some European glacier that was threatening some village several centuries ago. The villagers went to the Pope asking him to pray that the glacier would retreat. Recently villagers from the same region went to the Pope, asking him to pray for the same glacier which has nearly disappeared." [Sorry, I do not speak english very well] The story you tell about concerns the largest glacier in western europa, the Aletsch glacier in Switzerland. Here is the news in french I know well the story, because I live in this area of Switzerland. Retreating glacier is a realty that every people living in the alps experience.
        Response: Thanks for the link (I was hoping someone would post some more info). It's a great story - the villagers of Fiesch swore to live a virtuous life and prayed against the growth of the Aletsch Glacier. To enhance the effect of prayer, they've held an annual procession every year since 1862. Now that the glacier is melting, the people are trying to get a meeting with the Pope to request he cancel the Papal oath. You can't make this stuff up.
        
        I'm now waiting for a new skeptic argument: "global warming was caused by the Pope".
121926. NicklasE at 18:27 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        There are a few things missing in this blog that upsets me: 1) Figure 1. It's a nice graph but how does this graph relate to the total mass of the ice sheet? 2) Your claim is that CO2 is driving the slope of figure 1, but you don't compare with any estimates of how that figure would look like if we did not add any extra CO2 into the atmosphere from burning fossil fuels. My guess is that the figure 1 would look virtually the same. 3) With the current rate of mass reduction of the ice sheet it will take x years for everything to melt. You claim that we will reach a tipping point causing a drastic reduction of x. Do you have any example or good explanation to this claim making it plausible?
        Response: "It's a nice graph but how does this graph relate to the total mass of the ice sheet?"
        
        Figure 1 is the change in total mass of the Greenland ice sheet. This is measured by satellites which measure the change in the gravity field around Greenland (Velicogna 2009).
        
        "you don't compare with any estimates of how that figure would look like if we did not add any extra CO2 into the atmosphere"
        
        If we hadn't added any extra CO2 into the atmosphere, we would have experienced a slight, long-term cooling trend over the last half century (Meehl 2004). It's difficult to see how Greenland could lose ice mass at an accelerating rate if global temperatures were cooling.
        
        "Do you have any example or good explanation to this claim making it plausible?"
        
        A good example of the high sensitivity of ice sheets to warmer temperatures is the behaviour of ice sheets 125,000 years ago. At this time, temperatures were 1 to 2°C warmer than current conditions. Sea levels were at least 6.6 metres higher than current values. This is strong evidence that ice sheets are sensitive to sustained warmer temperatures (Kopp 2009).
        
        How does it happen? The Greenland and West Antarctic ice sheets sit on bedrock that is underwater. As the oceans warm, they melt the ice sheets from below - this causes the ice sheets to slide faster into the ocean (van den Broeke et al 2009). This is what is being observed now by satellites.
        
        It's not fantasy, it's not alarmism, it's peer-reviewed science based on multiple lines of empirical observations.
121927. HumanityRules at 18:11 PM on 24 March 2010
        A peer-reviewed response to McLean's El Nino paper
        Here is Mclean et als reply to the Foster comment. Warning: this is not peer-reviewed (this becomes obvious very quickly). It also contains reference to the climategate emails which I know some people are a little sensitive about. http://icecap.us/index.php/go/joes-blog http://icecap.us/images/uploads/McLeanetalSPPIpaper2Z-March24.pdf
121928. David Horton at 17:37 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Well, this is a new one on me. What Mr Camel is saying is that all us evil greenies who want to reduce CO2 are dooming the poor peasants of Switzerland to having glaciers advance down the valleys and ruin their farms (unless, of course, the present pope could stop it, rather like King Canute with liquid ice). So we should all shut up and applaud the increase in CO2. I guess it's a variant on "They call CO2 a pollutant, we call it plant food" nonsense - "They call CO2 a pollutant, we call it a glacier killer". Still, it has served up a bit of amusement on a Wednesday afternoon.
121929. Philippe Chantreau at 15:19 PM on 24 March 2010
        Skeptical Science housekeeping: Contradictions, URLs and getting hacked
        Svalgaard is by no means a denialist. I don't know how active he has been regarding publications lately but I am pretty sure that he would not submit low quality stuff and I'm quite sure you won't see his work in E&E. I don't think he's even that interested in climate science itself.
121930. acerj at 15:19 PM on 24 March 2010
        Mars is warming
        Actually Sagan, temp measures on other planets could be considered more reliable than some I've seen taken on earth. You are showing an obvious bias. If we are concerned with finding the truth why not look at other planets.
121931. gallopingcamel at 15:08 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        David Horton (#35), Scott Mandia is committed to the AGW cause but he does not try to deny history. I am quite a fan of his although I seldom agree with him on mankind's role in what is going on with climate. Expanding glaciers during the "Little Ice Age" caused all kinds of problems. In Switzerland they kept very good records so we know that farmers were having difficulty paying their taxes and that wheat prices seem to be a plausible proxy for average temperatures (Herschel). Take a look at the following link before you start rooting for bigger and better glaciers: http://www2.sunysuffolk.edu/mandias/lia/little_ice_age.html
        Response: This reminds me of an story I heard recently - I don't recall the exact details (a google challenge for the curious) but there was some European glacier that was threatening some village several centuries ago. The villagers went to the Pope asking him to pray that the glacier would retreat. Recently villagers from the same region went to the Pope, asking him to pray for the same glacier which has nearly disappeared.
        
        Just an amusing anecdote. More seriously, noone is wishing for glaciers to grow and take over the regions that we inhabit. There is no danger of that happening. But what is of serious concern is that the glaciers that seasonally melt and provide summer drinking water are retreating at an accelerating rate. This threatens the water supplies of hundreds of millions of people. Well, hundreds of millions of people now. By the time the glaciers have disappeared, I imagine it will be significantly more people that are affected.
121932. David Horton at 14:43 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        "What is wrong with shrinking glaciers?" as well as the practical impact on water supplies there is the canary in the coal mine aspect. Mr Camel and his like constantly complain about the use of models in climate research, but with the glaciers shrinking so rapidly in recent times we have another example of the reality of warming climates. Mr Camel is really asking two questions in one of course. First is the "this is perfectly natural" meme, and second is the "what is the ideal temperature" meme. We've heard them a thousand times, and asking them in a slightly different way doesn't fool anyone. But how on Earth these people get their head around the concept that all these rapid changes to the Earth's biosphere exactly correspond to the rapidly rising CO2 levels and temperatures of the last few decades, and yet, it seems, are just purely coincidental ("glaciers could shrink or grow any old time, they just happen to have decided to shrink now, big deal") is beyond me. But I'm a simple soul.
121933. scaddenp at 13:52 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        "What is wrong with shrinking glaciers?" Ideally we want glaciers melting at a rate that doesnt cause sealevel to rise faster than we can adapt. 3mm/yr isnt good. 10mm/year would be tough.
        Response: Just off the top of my head, the sea level rise due to melting glaciers (excluding the Greenland and Antarctic ice sheets) is somewhere between 60 to 80 cm. Which would be inconvenient but not disastrous. The real sea level rise comes from Greenland and Antarctica.
        
        The more serious impact from disappearing glaciers is the eventual loss of a source of seasonal drinking water for hundreds of millions of people.
121934. gallopingcamel at 13:35 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Figure 3 at the top of this thread shows predictions for the CO2 concentration until 2100. The exponential rise assumed by the IPCC, Rahmstoorf and Hoffman is not the only plausible explanation for the observed concentrations. You folks don't have much time for Craig Loehle since Loehle & McCullough, 2008 but here he is again with an alternate view of things: http://www.ncasi.org/publications/Detail.aspx?id=3282
121935. bill at 13:25 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Thanks for this great website. As a farmer I am constantly defending the science of AGW against the farmers I come across who think it all a just a normal climatic cycle/socialist plot(70% if you believe a recent survey in southern Australia). The common refrain from the people I speak to seems to be; "Scientists huh, what the **** would they know?!" This site gives me the ability to put the counter argument although I fear that I'm fighting a losing battle. My rainfall here has dropped off 20% in the past 15 years which may not in itself prove much but given everything else that's happening it certainly worries me. Keep up the great work!
121936. gallopingcamel at 13:09 PM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Ned, (#7&8), Do you want glaciers to start growing again as they did during the Little Ice Age? What is wrong with shrinking glaciers? You seem to be well aware that sea levels rose very rapidly at the start of the present Interglacial. With regard to meltwater pulses, Disney did a good job on a collapsing ice dam in "Ice Age".
121937. Ned at 11:15 AM on 24 March 2010
        The 5 characteristics of scientific denialism
        Aha, yet another replication of Tamino's conclusion that the GHCN stations that dropped out before 1991 have a similar trend to those that did not drop out: # GHCN Processor v1.0 by Residual Analysis # Graph of the results It seems to nicely match the previous results from Tamino, Zeke Hausfather, and Ron Broberg. More to the point, Joseph seems to have come up with a really nifty and flexible program for doing these kinds of studies.
        Response: Thanks for the link, I've added it to the list of links on the 'Dropped stations introduce warming bias' argument (and while I've got everyones' attention, a quick exhortation to submit any useful links you might encounter so we can build a comprehensive resource of useful global warming links).
121938. Ned at 09:39 AM on 24 March 2010
        Human CO2 is a tiny % of CO2 emissions
        Vinny Burgoo writes: Which gives a net annual increase of 25 Gt. That's nearly twice the number you quote in your 'What the science says...' section and five or six times times the number offered by the Mauna Loa observatory. (+2 ppm CO2 pa is about +4 gigatonnes CO2, no?) You might be making the same error that oracle2world made in the comment immediately preceding yours. According to CDIAC, "1 ppm by volume of atmosphere CO2 = 2.13 Gt C" But 1 GT C = 3.67 GT CO2. So +2 ppm a^-1 is about +15.6 GT CO2.
121939. Jesús Rosino at 08:34 AM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Thanks for your inline answer in #20, John. The trends in modelled and observed CO2 concentrations are truly close, almost indistinguishable. I link another graph from the IPCC: graph website
121940. Vinny Burgoo at 08:11 AM on 24 March 2010
        Human CO2 is a tiny % of CO2 emissions
        I'm looking for a rough estimate of net human CO2 emissions as a percentage of net natural emissions. (I know. Meaningless. But I'm checking a claim by a respected climate scientist who thought it worthwhile to scare some NZ brewers with such an estimate. His was 10%.*) This page looked like a likely source but I can't get your numbers to behave. Please tell me what I'm doing wrong. Net(?) human emissions: 29 Gt Net natural emissions: (220+220+332)-(450+338-0.4x29) = -4 Gt Which gives a net annual increase of 25 Gt. That's nearly twice the number you quote in your 'What the science says...' section and five or six times times the number offered by the Mauna Loa observatory. (+2 ppm CO2 pa is about +4 gigatonnes CO2, no?) What's occurring? *Salinger actually wrote that 'Human inputs are about 10% of the natural cycle', which is gibberish. If he meant 'about 10% of natural inputs', he's clearly wrong. If he meant 'net human inputs are about 10% of net natural inputs'... That's what I'm trying to find out. Incidentally, in the same presentation he also claimed that 'Human energy use [is] nearly half of total solar input to Earth'. He was off by about four noughts with that one. Or is it three? Enough to get him sacked, anyway. I dunno Alarmists!
121941. muoncounter at 07:47 AM on 24 March 2010
        CO2 levels during the late Ordovician
        Whoa! There needs to be a geologic timeout here. Way back at 50, Peter Hogarth mentioned "None of this work precludes other drivers (lesser or greater) for global temperature and climate, and in geological history as well as now, other factors must be taken into account (such as insolation, plate tectonics, etc)" It is vastly out of context to make any comparisons between the present and the distant geologic past without plate tectonics. The globe looked very different 450 million years ago: no land mass at the North Pole and a super-continent at the South Pole. That paleo-geography is a major control on oceanic circulation and thus on climate is well-established among geologists. See this discussion of the Ordovician of eastern North America for an example. Some of the best evidence for Ordovician glaciation is in the present day Sahara and in South America; these areas were near the South Pole at the time. See also this summary article on the Ordovician climate, concluding thus: "It therefore seems likely that it was geographical factors, rather than the chemical composition of the air, which played a key role in triggering that glacial period."
121942. Alexandre at 07:27 AM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        muoncounter, Thanks for the interesting study you linked. I was thinking of the fact that in the Pliocene warm period, Greenland was the only lend ice mass left. So if Greenland ice sheet is gone because of AGW, land ice will all be gone in the NH by then, probably. "Resilient" was probably a poor choice of words, I admit, since it implies the ability of returning to its original state. I see the paper you linked suggests otherwise. "The hardest land ice region to melt in the NH" would be more appropriate, maybe?
121943. shargash at 06:00 AM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Oops...sorry about repeating the points in CBDunkerson's post. I had mine all typed in (at work) and someone called me away from my desk right before I hit submit. By the time I came back and hit submit, CBDunkerson had scooped me.
121944. shargash at 05:58 AM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        " The link below shows that the Greenland ice sheet was less extensive during the MWP" There is a bit of apples-to-oranges comparison involved in that. You are comparing the MWP minimum against the current incomplete melting. There is a lag between CO2 rise and temperature rise, and there is a lot of inertia in the ice sheet. Even CO2 levels were to stop rising today, we don't know that the melting already baked in isn't much greater than the MWP melting.
121945. Leo G at 05:48 AM on 24 March 2010
        Skeptical Science housekeeping: Contradictions, URLs and getting hacked
        HR and Ned, here is Dr. Svalgaard's own words about his position; "John L (15:38:59) : Can someone, perhaps Leif Svalgaard himself, point me to a single argument, debate, website, presentation, speech, paper, etc. where Leif explains why exactly he considers himself a skeptic, or lukewarmer, or a…whatever? For the record: 1) Temperatures are higher now than 100 years ago. Exactly how much can be discussed [fakings, UHI, etc]. 2) Solar activity has been ‘flat’ since 1700 with a ~100-yr ‘cycle’ on top. It is not clear if this ‘cycle’ is a real cycle or just a random fluctuation. 3) Solar activity and cosmic ray modulation do not go away during Grand Minima [although sunspots are less visible] 4) There is a 0.1% change of TSI between solar min and solar max, resulting ~0.1C temperature variation 5) No long-term variation of TSI has been demonstrated 6) No convincing evidence for a sizable solar modulation of climate has been demonstrated 7) No convincing evidence for CO2 being the cause of the warming [see point 1] 8) In the deep past [billions of years] CO2 was a significant greenhouse gas, because of its much higher partial pressure than today 9) Solar models are not good enough for detailed prediction, but our understanding of the solar interior and explanation of energy production are on firm footing 10) Solar polar fields seem to be a useful predictor [and it is semi-understood why] 11) Climate models have not been very successful, but should work in principle 12) Both the Sun and the Earth can exhibit ‘internal’ cycles. E.g. some stars pulsate and change luminosity on a large scale [50-100%] 13) Various ‘external’ influences [planets, galactic 'positions', interstellar clouds, electric currents from the galaxy, etc] are either not operating or their effects are negligible 14) The cosmic rays vary too little to have any effect and the mechanism proposed does not seem to work [you can always extend your belief a bit by claiming that more data is needed] Considering the above, I don’t know what you would call me. And I don’t care"
121946. muoncounter at 05:45 AM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        John, Answered my own question with this graph . Full scale here. This somewhat longer term trend is indeed down. Should be smooth sailing through the Northwest Passage.
121947. muoncounter at 05:34 AM on 24 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        John, Nice work, albeit very scary.I wonder how figure 1 (Greenland ice mass loss, from Velicogna) would compare with a graph of ice loss data from Arctic observations at nsidc.org. A quadratic trend as shown has ghastly implications. Alexandre, I wonder about your remark in 24, "apparently we're talking about the most resilient land ice mass in the Northern Hemiphere." A study entitled "Climatic impact of a Greenland deglaciation and its possible irreversibility," published in the 2004 Journal of Climate, available here, makes a case quite to the contrary. The authors took the well-established effect of post-glacial isostatic rebound into account, showing that an ice-free Greenland would rise so that there would no longer be an accumulation zone. Once its gone, its gone. To quote Randy Newman, "Boom goes London, boom Paree." As far as time scale of these potential events is concerned, there is ample geologic evidence that glacial melt and associated freshwater runoff can indeed be sudden. See this Goddard Institute study of "meltwater pulses." In short, the mechanism (discussed at length here, is thus: Warming causes meltwater to pond locally, forming large lakes trapped behind localized "ice dams." Breaching an ice dam can happen quickly, resulting in catastrophic flooding (I've seen the sedimentary evidence left by these floods first-hand). And as the land mass becomes ice-free, it rises to seek gravitational equilibrium.
121948. Tom Dayton at 02:40 AM on 24 March 2010
        The 5 characteristics of scientific denialism
        RSVP, we experimental psychologists say "There are the hard sciences, and then there are the really difficult sciences." Every year, thousands of students in labs for classes dutifully execute psychological lab experiments that always have yielded the same, predicted-by-theory results for the previous tens of thousands of students over the previous many decades. Experimental psychology has a long history. Even the brief entry in Wikipedia reveals your statements to be false. But your bigger error was equating the scientific method to "predicting and reproducing results in a lab." Most broadly, science is what scientists do.
121949. CBDunkerson at 23:26 PM on 23 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        Gallopingcamel, there is 'comparing apples to oranges' and then there is what you did above. John wrote about a global change in temperature which the IPCC has projected for the year 2100... you 'countered' with a (disputed) local change in ice coverage compared to current levels. Each of those discrepancies (i.e. global vs local, temperature vs ice coverage, and 2100+ versus current) potentially invalidates the 'comparison'. Together they make it incomprehensible.
121950. Alexandre at 22:42 PM on 23 March 2010
        What CO2 level would cause the Greenland ice sheet to collapse?
        JMurphy, Thanks for the response. Ok, so the only remaining land ice mass was significantly reduced - we might say collapsed? What caught my attention here was the 3 degree warming and the remaining ice sheet. But you're right: "remaining" does not mean "unchanged". One important point to stress here, is that apparently we're talking about the most resilient land ice mass in the Northern Hemiphere. So if Greenland feels it, than Siberia and all its permafrost will feel much more...

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