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Comments 126551 to 126600:

126551. RSVP at 19:53 PM on 14 November 2009
        An overview of Greenland ice trends
        John, Sorry if I came across that way. My comment was only in reference to the math error, and I appreciated Mizimi's pointing it out. By the way, he also says something later that seems reasonable, implying that the ice mass acceleration is not necessarily a constant, and would tend to diminish as soon as the bulk of the peripheral ice fields disappear. I am sure the problem is much more complex, and even the simplest models would depend on a series of functions that reflect the dynamics of various stages. Personally, I dont think it is at all realistic to extrapolate to 436 based on a second derivative extracted from the fuzz of nine samples. It is however useful to give some feel of a worst case scenario and perhaps what is possible. However, another very simple calculation with the same data leads to very different conclusion. That is to assume acceleration is zero or neutral, but that the ice loss rate (slope) is constant at the current rate. From the curve, we see about 1500 x 10e9 T/year over a 6 year period, which equals 250x10e9 T/year. Using the same value for total ice... 2.85 x 10e15 T / 250 x 10e9 T/y = 11,400 years.
126552. Philippe Chantreau at 18:56 PM on 14 November 2009
        An overview of Greenland ice trends
        Mizimi, as ice is shed, isostatic rebound could bring the underlying land quite a bit higher, so all that ice might not be as safely land locked as you say.
126553. Riccardo at 07:49 AM on 14 November 2009
        An overview of Greenland ice trends
        RSVP, i didn't want to say that the GIS might collapse altogether. There might be partial collapse along the slopes at the edges. How comes that GIS cannot release all of it's ice? Given that we are heading toward temperatures never seen in the last several hundreds thousands years (not just 100,000), the GIS is definitely capable of releasing all of its ice and allow a 7 m sea level rise. It's just a matter of how much warming and how much time it takes.
126554. Mizimi at 04:51 AM on 14 November 2009
        An overview of Greenland ice trends
        The Greenland ice sheet cannot 'collapse'. The ice sheet sits in a basin around 300m below sea level surrounded by mountains...whether the basin is due to the weight of the ice or was there originally is not clear. What is clear from core samples is that the central and most massive portion of the ice sheet has not changed for over 100,000 years. What we are seeing now is increased melt and ablation at the edges of the ice sheet which ,if it continues, will diminish as the central sheet becomes unable to sustain the flow outwards. So there cannot be a collapse and no 7m rise in sea level.
126555. Steve L at 04:50 AM on 14 November 2009
        The albedo effect
        At the risk of encouraging nonsense, Henry Pool (#20) -- where do you find CO2 reflecting a lot of sunlight? My understanding is that it is mostly invisible to visible light but opaque to infra-red.
126556. Riccardo at 03:44 AM on 14 November 2009
        An overview of Greenland ice trends
        RSVP, i've never thought of doing this rough calculations. This means that assuming not even partial rapid collapse of the ice sheet we'd get 16 mm/yr, 1.6 m in a century, from Greenland alone. Pretty scaring, indeed; let's hope it will slow down. Take it easy Greenland!! :)
126557. RSVP at 02:09 AM on 14 November 2009
        An overview of Greenland ice trends
        To Mizimi Thank you for pointing out my error. You are right about the exponent, which was also missing in the denominator. Plugging new values in gives us... years = sqr(2 x 2.85 x 10e15/30 x 10e9) = 436 years hmmmm... how long do you have to boil a hat to optimize digestion?
        Response: You're remarkably blase about the potential 7 metres sea level rise from the collapse of the Greenland ice sheet not to mention a similar contribution from the Antarctic ice sheet. Surely you realise the impact of such a sea level rise on humanity.
126558. chris at 01:58 AM on 14 November 2009
        An overview of Greenland ice trends
        today's Science has a relevant paper: M. van den Broeke et al. (2009) Partitioning Recent Greenland Mass Loss Science 326, 984-986 (November 13, 2009) http://www.sciencemag.org/cgi/content/abstract/326/5955/984 abstract: Mass budget calculations, validated with satellite gravity observations [from the Gravity Recovery and Climate Experiment (GRACE) satellites], enable us to quantify the individual components of recent Greenland mass loss. The total 2000–2008 mass loss of ~1500 gigatons, equivalent to 0.46 millimeters per year of global sea level rise, is equally split between surface processes (runoff and precipitation) and ice dynamics. Without the moderating effects of increased snowfall and refreezing, post-1996 Greenland ice sheet mass losses would have been 100% higher. Since 2006, high summer melt rates have increased Greenland ice sheet mass loss to 273 gigatons per year (0.75 millimeters per year of equivalent sea level rise). The seasonal cycle in surface mass balance fully accounts for detrended GRACE mass variations, confirming insignificant subannual variation in ice sheet discharge.
126559. chris at 22:57 PM on 13 November 2009
        An overview of Greenland ice trends
        re #10 (i) Your first point is incorrect HumanityRules on two levels (I think you've misread Milne et al.) Firstly the data isn't from one type of measure, from one locality. Milne is using the Maine salt marsh data as a detailed illustration of local relative sea level variability. However their paper is a review, and their conclusions come also from other papers cited(specifically, as they indicate, from coral microattols from the Cook Islands; foraminifera from peat deposits on the Connecticut coast; salt marshes on the coast of Denmark). And there are many other examples including the papers I cited on relative sea level variation in NW Europe in post #9. The bigger error, is to mistake local relative sea level for global eustatic sea level. Milne et al present the evidence that even considering local variation in sea level (that may have post glacal isostatic and land subsidence contributions etc.), this is smallish (generally 1-10 cm per century). (ii) Let's look at global eustatic sea level. You've linked to another unattributed picture in your post. This turns out to be a model of past and projected sea level rise from this paper [*]. Presumably you want us to take it at face value, so let's do so: (a) Grinsted et al use historical temperature data to estimate possible sea level variation during the last 2000 years. For example, they suggest that during the period from around 600 AD to 1150 AD in the Medieval Warm period), sea levels might have risen by around 25 cm. This is about 15% of the sea level rise during the same period in the earlier picture you linked to in your post #3 (which presumably you now reject; they can’t both be correct). It corresponds to a bit over 2 cm per century. If one takes the Grinsted analysis at face value we may well expect around 1 metre of sea level rise during the 21st century. (b) So the data you’ve presented to us indicates the sea level rise of the 21st century may occur at close to 50 times the rate of sea level rise associated with what is considered to be the transition to the warmest period in the previous 2000 years before the middle of the 20th century (sea levels are already rising around 15 times more quickly than during the period pictured in the graph you linked to). If you were to put the projected 21st century rise on the same horizontal time scale as the previous 2000 years in your picture, it would be near vertical. Isn't this all pretty consistent with Milne et al.? They review data that shows rather little preindustrial variation in eustatic sea level; that current measurements show sea levels are already rising much faster (by more than 10-fold) that even during the rise to the MWP; and that we are pretty certain to get significantly increased rates during the current century. It's certainly inconsistent with the old graph you linked to from that dodgy web site (your post #3). (iii) In a previous post (#8) you asked the question "Would you put 100% of the sea level rise this century down to AGW?". If you look more widely at the NERC Planet Earth site from which you cut and pasted that lonely figure from Grinsted et al (2009) you would have found an analysis that addresses your question: http://planetearth.nerc.ac.uk/news/story.aspx?id=551 Jevrejeva et al determine that almost 80% of sea level rise during the 20th century is as a result of anthropogenic greenhouse forcing. In fact they point out that the anthropogenic contribution to sea level rise was likely suppressed somewhat by volcanic eruptions: "If no volcanic eruptions had happened since 1880, then sea-level rise over the last century would've been seven centimetres higher than it was," explains Jevrejeva. [*]A. Grinsted et al. (2009) Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD Climate Dynamics; in press. [**] Jevrejeva, S et al (2009) Anthropogenic forcing dominates sea level rise since 1850 Geophys. Res. Lett., doi:10.1029/2009GL040216, in press.
126560. Mizimi at 22:52 PM on 13 November 2009
        An overview of Greenland ice trends
        RSVP: your sums are a bit out I think.... A km3 of ice is 10E9 tonnes ( roughly),so 2.85 x 10E6km3 is 2.85 x 10E15 tonnes. Since 2002 the loss is 1100 x 10E9 tonnes, or 157 x 10E9 T/yr as an average - so if the rate continues in a linear fashion it would take around 10,000 years to melt all the ice ( which cannot happen). But the rate is accelerating at around 30Gt/yr so in 5 yrs the loss will be around 300Gt/yr.
126561. RSVP at 22:12 PM on 13 November 2009
        An overview of Greenland ice trends
        Sorry. Looking at the units, I see I forgot to add another assumption. That 1 m3 of ice weighs one ton, which it does not. At any rate, it is probably close enough to give an idea of the general order of magnitude in years. Should anyone really be concerned even if it were 10,000 or 5,000 years?
126562. RSVP at 20:45 PM on 13 November 2009
        An overview of Greenland ice trends
        I was going to ask what the total amount of ice there was in Greenland, but then realized this was a dumb question when I could just look it up. So I did. http://en.wikipedia.org/wiki/Greenland_ice_sheet says it is 2.85 x 10e6 km3, or 2.85 x 10e9 m3 . Sounds like a lot of ice. Then taking your acceleration of 30 x 10e9 tons/yr2, (if we ignore the initial condition) this equates to solving this as a falling body at rest d=(1/2)gt2. Solving for t, leads to years = sqr(2 x 2.85 x 10e9/30) = 13,784 years. Sounds like a lot of ice up there.
126563. bcbwilla at 16:21 PM on 13 November 2009
        1934 - hottest year on record
        Will Nitschke, you asked for an explanation as to why the "2% land mass of the United States has only an 'infinitesimal effect on global trends' yet the 3% land area of the Arctic is apparently significant 'concrete' proof?". Your argument is a strawman. No one is claiming that what is happening in the Arctic alone is "significant 'concrete' proof". Your comparison would be fair only if those arguing that GW is happening are basing their arguments entirely on what is happening in the Arctic and no where else, but this is absolutely not true. What is happening in the Arctic, along with what is happening elsewhere around the globe is what is considered.
126564. HumanityRules at 12:52 PM on 13 November 2009
        An overview of Greenland ice trends
        I've only had time to read the Milne paper. Here's the PDF for those interested. 'These data indicate that local rates were generally at the 1–10 cm per century level" As you know this data is from one type of measure, salt-marsh stratigraphy, that work was done in one local (East Maine) so as you pointed out to me one localality shouldn't be used to represent global averages. The papers presentation of a much wider selection of data is informative That paper is eye openning in its honesty about the number of variables and inherent difficulties associated with these sort of measurements. I read Milne and took from that not that we could give definitive numbers to the last 2000years of sea level and beyond but that the science still has a long way to go. I still don't think anything presented in that paper says stasis for 2000years followed by rises in the industrial age. From what I read the rise in the 20th century was between 10-30cm depending on which data set you use. In table one Milne says the salt marsh data covers the last 500years and the maximum sea level change within that period is 20cm/century Also this graph is useful, try to ignore the pending apocalypse portrayed for the future and focus on the little hill around 1200AD (the Medieval Warm Period???) when sea levels were higher than today. Back to Greenland by way of North America There is something that caught my attention a while back and which was briefly mentioned in the Milne paper, the Laurentide ice sheet. This was a huge ice sheet that cover North america down to New York and slow melted over the past 20000 years. You could see the Greenland ice sheet as the remmnents of it. There is a cartoon of it's historical retreat here. I was wondering how that fits in with long term story of the Greenland ice sheet? It should be noted that the retreat hasn't been an even process and at times it's even grown. I wonder whether we should expect anything other than a retreating Greenland ice sheet?
126565. chris at 05:12 AM on 13 November 2009
        An overview of Greenland ice trends
        re #8 It's worth pursuing this point, since Greenland ice melt, past, present and future, is quite relevant for sea-level change past, present and future (so necessarily off-topic!). The Dutch data you linked to is difficult to assess since none of the links to the data on that web site are live. So we can’t tell what the Dutch data is, where it was taken, and whether it refers to local relative sea level (I suspect it does) or global eustatic sea level (very likely not). However we can look at data published in recent years that bear specifically on mid-late Holocene sea level variation in the coastal regions near and around Holland, and more generally at papers that assess late Holocene variation in global eustatic sea level, in other words the absolute change in sea level arising from warming/cooling and mass influx (ice sheet melting) and decrease (ice sheet expansion), that is independent of the local post-glacial isostatic effects, land subsidence, and so on, that can give rise to spurious interpretations. So on local (Dutch and environs) late Holocene sea levels, an analysis of sea levels from a region less than 100 miles to the NE of N Holland doesn’t show any up-down variation in regional sea level during the Holocene, although there has been a step-wise increase in relative sea level during the mid-late Holocene, largely due to post-glacial subsidence: Bungenstock F, Schafer A (2009) Holocene relative sea-level curve for the tidal basin of the barrier island Langeoog, German Bight, Southern North Sea, Global Planet. Change 66, 34-51 Likewise, a very comprehensive analysis of Holocene sea level data that covers a large chunk of the NW European coast (the coasts of Germany, Belgium, Holland) indicates very little upwards and downwards variation in sea level. There is a general rapid rise to around 6000 years ago with much slower subsequent sea level rise, and the data fit well to eustatic sea level analyses indicating rather little rise or fluctuations during the last 2000 years: Vink A et al (2007) Holocene relative sea-level change, isostatic subsidence and the radial viscosity structure of the mantle of northwest Europe (Belgium, the Netherlands, Germany, southern North Sea) Quatern. Sci. Rev. 26, 25-28 More generally a recent review of sea level change indicates that sea level variations have been of low amplitude throughout the couple of millennia before the industrial age: G.A. Milne et al (2009) Identifying the causes of sea-level change Nature Geosci. 2, 471-478

        Sea-level observations for the mid- to late Holocene provide constraints on the natural variability of sea-level change immediately preceding the industrial revolution. These data indicate that local rates were generally at the 1–10 cm per century level (see Table 1).

        So considering the relevant global parameter of eustatic sea level variation resulting from ice sheet/glacier mass balance and ocean temperature variations, there doesn’t seem to be much evidence for very significant fluctuations in global sea level, at least in the couple of millenia before the industrial age. Even if we consider local relative sea level where postglacial isostatic effects, land subsidence, tidal range variations and so on influence the local sea level, I can't find anything that shows the variability in the unattributed data set you linked to, and that includes data in papers that cover the equivalent coastal region (see papers cited above). If you could find the source of the data you linked to I'm mildly curious to see what it actually is... I don't think this is at all straightforward, and there is still uncertainty in mid-late Holocene sea level variation. However there just doesn't seem to be any evidence for the large scale fluctuations that your link might imply, and the recent papers/reviews on this support the opposite interpretation. I'm afraid I haven't found downloadable versions of the papers cited...
126566. chris at 01:58 AM on 13 November 2009
        The albedo effect
        re #20 That simply doesn't accord with the evidence Henry. Analysis of earth surface temperature data indicates that apart from the hugely transiently amplified 1998 temperature (largest El Nino of the last century), surface temperatures maxed around 2005. All of the years of the current decade are warmer (by around 0.2 oC on average) than all of the years of the 1990's apart from the anomalous 1998: NASA GISS: http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts+dSST.txt UK HADCRUT: http://www.cru.uea.ac.uk/cru/data/temperature/hadcrut3vgl.txt One could say that temperatures haven't risen since around 2005, but you simply can't make that sort of interpretation from a few years worth of data that incorporates large interannual variability. What do we expect the earth's surface temperature to have done during the last several years? We know categorically that the sun has dropped from the top to the bottom of its solar cycle from around 2002 to now (it's just starting on its upturn). There's pretty good evidence that the solar cycle contribution is around 0.1 oC of cooling, max to min (and obviously 0.1 oC of warming min to max). So we expect all of the greenhouse warming contribution since around 2003 (~ 0.15-0.2 oC per decade) to be negated by the small solar cycle cooling between around 2003 and now. It's therefore not surprising that surface temperatures haven't yet gone above the 2005 levels in the last few years. That's pretty much what we expect. This leads to a serious problem with those attempts to assign a cooling trend (for which there isn't any evidence in the surface temperature records) to albedo, or ocean regimes, or amplified solar effects or whatever, namely that these effects should have caused the earths surface to cool significantly during the last decade if they existed. Either that or the earth's surface temperature is much more sensitive to greenhouse warming that the science indicates. I suspect we'll find (as Palle et al. 2009 state quite explicitly), that there hasn't been a significant increase in albedo since 2000, and in any case (as Palle et al, 2006 state quite explicitly), an albedo change due to secular cloud variation doesn't necessarily inply a surface temperature response since clouds have warming ("heat trapping") as well as cooling (albedo) effects. E. Pallé et al (2006) Can Earth's Albedo and Surface Temperatures Increase Together? Eos Trans. AGU, 87(4), doi:10.1029/2006EO040002 Palle et al. (2009) Inter-annual variations in Earth's reflectance, 1999-2007 J. Geophys. Res. 114, D00D03
126567. Henry Pool at 01:33 AM on 13 November 2009
        The albedo effect
        if I look carefully at our World Climate Widget, (watts up with that) it looks to me that since about 2001 we have a slight decline in global warming, or shall we say: global cooling has started. This seems to coincide with the increase in earth’s albedo, http://wattsupwiththat.com/2007/10/17/earths-albedo-tells-a-interesting-story/ although I think this graph may need some updating (look Palle et al 2008) As I suspected, I found that at the same time ozone has begun increasing. http://atmoz.org/blog/2007/09/05/ozone-hole-update/ I also note that CO2 is increasing (it seems there is no doubt about that). CO2 also reflects sunlight. We also note that water vapor is increasing, due to human activities, mostly shallow water (dams for consumption and irrigation). So all in all, I think the increase in earth’s albedo will hold, and it wipes out the effect normally attributed greenhouse gases
        Response: This theory is invalidated by the fact that our climate is still accumulating heat. It's still in positive energy imbalance. From 2003 to 2008, the world's oceans have been absorbing heat at a rate of 0.77Wm-2.
126568. HumanityRules at 12:21 PM on 12 November 2009
        An overview of Greenland ice trends
        Response and #5 I take your points but teh climateaudit graph shows rises and falls over the last 2000years with no real nett change. I'm aware that misleading data supporting sea level rises has been used in the past. From memory, data from around Hong Kong and a Pacific Island (i think Tuvalu). So certainly making the correct measurements is important. No nett change can still mean ups and downs in the intervening time. And the recent up needs to be put into that context. I guess the point I'm making is that to argue absolutely no change over the last 2000years followed by sudden rise during the industrial age would be extremely damming. But putting the recent change into the context of a naturally dynamic system, which is undoubtedly the case, requires a little more sophisication. Would you put 100% of the sea level rise this century down to AGW? Sorry this has strayed off topic from Greenland
126569. Riccardo at 09:57 AM on 12 November 2009
        An overview of Greenland ice trends
        As the authors themselves say, it is "the classic pattern expected in a warming climate, with increased snowfall in the interior and enhanced runoff from the marginal ablation zone." Also noteworthy is that they date the onset of significant response of the ice sheet to 1990.
126570. canbanjo at 08:48 AM on 12 November 2009
        An overview of Antarctic ice trends
        there is an antarctic post on realclimate too.
        Response: I've updated your URL to directly link to the Antarctic post - it won't be on the RC homepage forever.
126571. Mizimi at 03:26 AM on 12 November 2009
        An overview of Greenland ice trends
        Analysis of surface mass balance "Results from the high-resolution run with RACMO2.1/GRN are shown in Figure 1. It is found that total annual precipitation on the Greenland ice sheet for 1958-2007 is up to 24% and surface mass balance up to 63% higher than previously thought." and.. "RACMO2.1/GRN is able to simulate a realistic spatial and temporal SMB for the Greenland ice sheet for present-day climate conditions. Our findings show that considerably more mass accumulates on the GrIS than previously thought. The higher resolution, the used ice sheet mask and the redundant need for post-calibration could be a cause for disagreement between models." The combined graph of precip./melt/runoff/mass balance shows the beginning (maybe?) of a recovery from 2007.
        Response: Thanks for the link, I've turned it into a hyperlink as the URL was quite long. That data is a little older than the GRACE data which shows that ice mass loss has continued past 2007 - see Figure 2 above.
126572. Henry Pool at 02:30 AM on 12 November 2009
        It's ozone
        Nice. I asked everyone to give me the latest ozone graph and nobody says anything. Then I find it here on same site! Did you notice the upward trend since 1998? We or on the road back up the hill - but true - it is going slowly.Unfortunately the damage done by the CFC's must not be underestimated. But we are going up. I am confident that this will result in more of the sun's radiation being blocked. The CO2 going up will also help!~
126573. chris at 23:44 PM on 11 November 2009
        High CO2 in the past, Part 2
        re your points, HumanityRules: (i)& (ii) best to read the paper (click on the link in John Cook’s summary), and be careful in reading posts! Then it's obvious that: a. Figure 2 above from Royer 2006 is an "extremely low resolution" analysis (highly smoothed proxy record and a very coarsely-time resolved model) to assess the broad evolution of forcing from the slow solar constant increase in the light of a highly smoothed CO2 record/model b. the rest of the data in Royer 2006 presents data at "a much tighter time resolution". That's what I said in my post and that's quite obvious from Royer's review. Royer is addressing one point in his Figure 2, and another point in the rest of his article. (iii) good! (iv) That’s not right I think in two respects. First Royer shows the variations in CO2 and temperature/climate regimes throughout the Mesozoic (see Royer’s Figures 3 and 4). That's the relevant data. I don’t think there’s much evidence for significant Mesozoic glaciations, although there is evidence for cool spells in the Mesozoic (generally associated with low CO2 where contemporaneous proxies are available), with some warmer/hot periods associated with higher CO2. According to Retallack (2009) (the paper you cited, and many thanks for that), “The Mesozoic greenhouse was not hot with cool spells (Royer, 2006), but warm with hot flashes”, the hot flashes associated with raised CO2. An essential point though (and one that Retallack addresses) is that one can only make infererences about the relationships between temperature/climate regimes and CO2 levels where there are contemporaneous temp and CO2 proxies. So we should be careful not to assume that if temp (or CO2) was high at some point in time where we have a proxy, and high at some other time, that all the intermediate periods are defined. That’s likely to be wrong. I think in general we agree that the temperature/climate and CO2 records are bound to be spiky. That’s the conclusion to be drawn from the data in Royer 2006 and Retallack 2009. The other conclusion is that generally where there are contemporaneous CO2 and climate/temperature proxies the two are associated (high CO2 warm/low CO2 cold). That’s also the conclusion that Retallack (2009) draws. Here’s the abstract of Retallack, GJ (2009) cited in post #15: http://gsabulletin.gsapubs.org/content/121/9-10/1441.abstract
126574. chris at 21:07 PM on 11 November 2009
        An overview of Greenland ice trends
        re #3 The point refers to the effects of polar and land ice melt on sea levels as a result of the Glacial to Holocene transition. The evidence indicates that the bulk of this was realised by around 6000 years ago, and that for the last 2000 years, the nett change in sea level before around the last 100ish years was negligible (they may have actually gone down a tad in the period from the Roman era to the mid 19th century); so at the very least, any residual post-glacial melt has been balanced by snow deposition. Sea levels likely went up and down a bit during that period, but the modern increase in sea levels as a result of ocean warming and mountain and polar ice retreat is resulting in a nett rise in sea level (that is expected to accelerate as temperatures continue to rise). As pointed out already, the metric of interest is the eustatic sea level rise, which is the mean sea level. Obviously the effects of post glacial rebound and depression and local tectonic effects means that extreme care must be taken to assess eustatic sea leels and their changes that are independent of land surface changes. So in general eustatic sea levels are determined in the mid-latitude (Carribean/Meditteranean) far from direct effects of post-glacial rebound. Care must still be taken to assess other tectonic effects (e.g. the Greek mainland is sinking towards the SW as a result of collapse around the edges of the Tibetan plateau which has been pushed up (against its will!) by the Indian sub-continent. So eustatic sea level change is not a straightforward measure...
126575. Riccardo at 19:57 PM on 11 November 2009
        An overview of Greenland ice trends
        John, the Netherland and Denmark are on the same tectonic plate as the Scandinavian peninsula. As a boat that rise on one side and sink on the other when put away some weight from just one side, the plate is rising on the scandinavian side and sinking on the other side because there was much more ice on the scadinavian side of the plate.
126576. HumanityRules at 14:54 PM on 11 November 2009
        An overview of Greenland ice trends
        #2 "....analysis of sea levels in the late Holocene support the conclusion that ice sheet melt contributions to sea level rise had more or less come to equilibrium by around 3000 years ago (some evidence supports a lack of polar ice sheet contributions to sea level change by 6000 years ago). So although it’s not a straightforward analysis, the evidence indicates that sea levels have been pretty static at least for the 1000-2000 years before the mid-18th century, and the modern period of accelerating sea level rise encompasses only the last around 100-odd years" Have sea levels been unchanged for the past 1000-2000years? That is no change at all!! I realise this is from a skeptics website but the graph seems to tell a different story http://www.climateaudit.org/?p=61 . Can't confirm this Dutch finding but I'm prepared to believe in some variation in every natural process and not complete stasis until you hit the industrial age. Actually you would get what you describe if you put a trend line in that graph i.e. levelling out about 3000years ago but you would lose the detail that puts the recent sea level changes in perspective. In terms of the above article I still think you don't give full justice even to the data you present. In summary 1960s ~100 gigatonne loss 1970s-1980s no change 1990 rising to ~100 2007 347 gigatonne loss you suggest at the start of the article that data from 1958 will show accelerating ice loss. Half way thourgh you abandon the first section of the data to state "So we see a long term trend of accelerating ice mass loss since the 1970s". When in reality the data from 1958 to 1996 says steady or no loss. It still looks to me like you're relying on the last 6-7 years of GRACE data to cocclude accelerating ice loss.
        Response: Note that the climateaudit post you link to is talking about sea levels at one particular location in the Netherlands. The post also notes that "the part of the Netherlands which is below sea-level is sinking as a result of post-glacial rebound" (although I would've thought post-glacial rebound causes the land to rise - perhaps a mistype).
        
        "you suggest at the start of the article that data from 1958 will show accelerating ice loss"
        
        To be precise, I said we'll look at "long term trends going back to 1958". And what we find is a "long term trend of accelerating ice mass loss since the 1970s". We've gone from approximate mass balance to gradually increasing ice loss. This is independent of GRACE data.
126577. 10in10Diet.com at 13:29 PM on 11 November 2009
        Ice isn't melting
        In October we hit the all time low for October. http://climateprogress.org/2009/11/08/arctic-multiyear-sea-ice-nsidc-david-barber/ Lynn Shwadchuck
126578. HumanityRules at 13:06 PM on 11 November 2009
        High CO2 in the past, Part 2
        #13 thanks for changing the reference, I realized my mistake after posting. i) and ii) Fig 2 is from Royer 2006 it can't be simultaneously "....at extremely low resolution" (from your point i) and "....a much tighter time resolution" (from your point ii) iii) I'll try to look at them when I have time. iv) Its 'attractive' that the author can fit a couple or three ice ages into drips in the graph but there are also a couple of other ice ages there at periods of positive radiative forcing (not shown in the detailed graphs you talk about here) . The grey vertical lines indicating them are conviniently thin enough to be almost missed. and also high CO2 periods associated with cooler times in the more detailed graphs of fig3. Finally the mesozoic period, touched on in Fig3 and represented with "cooler?" periods has been shown by other authors while being generally a warmer period to also contain significant glaciation periods yet again Royer shows consistent positive radiative forcing. Can I add this to your list of papers Greenhouse crises of the past 300 million years Author(s): Retallack GJ Source: GEOLOGICAL SOCIETY OF AMERICA BULLETIN Volume: 121 Issue: 9-10 Pages: 1441-1455 My point would be that in reality a global temperature graph on that time scale would look more like a seismograph during an earth quake than the generally slow drops and rises shown on the radiative forcing graph above. I accept his attempt to get an overall general feel for climate change but think much, if not all, is lost in throwing away the detail.
126579. dopeydoctorjohn at 11:23 AM on 11 November 2009
        There is no consensus
        This crappy Doran study got a guernsey in the Letters page of the Sydney Morning Herald today, in a boldened piece from a university lecturer who, again, has accepted it without thinking seriously about it. Again, it is touted significant that a group who actively publish in a particular field, surprise, happen to believe in the field in which they are publishing. Again, that is not to deny that most Earth scientists agree with the current dominant paradigm Again, if 20% of Earth scientists can't even agree that humanity is making "a" significant contribution to warming, it would be interesting to hear their reasoning. And again, the only science the Doran paper represents is the science of "tautology".
126580. chris at 08:55 AM on 11 November 2009
        An overview of Greenland ice trends
        re #1; Yes Bamber’s paper is consistent with the general scientific observations that both Greenland and Antarctic mass balance loss is increasing:

        ”Thus, although there is a lack of consensus about the absolute value for the mass balance of the ice sheets, there is agreement that the trend has become increasingly negative for both Greenland and the WAIS.”

        There seems to be little doubt about that. You’ve selected a quote from Bamber’s article about the ice sheet responses. While it’s true that equilibrium responses are only realised on very long time scales (infinitely long in principle), analysis of sea levels in the late Holocene support the conclusion that ice sheet melt contributions to sea level rise had more or less come to equilibrium by around 3000 years ago (some evidence supports a lack of polar ice sheet contributions to sea level change by 6000 years ago). So although it’s not a straightforward analysis, the evidence indicates that sea levels have been pretty static at least for the 1000-2000 years before the mid-18th century, and the modern period of accelerating sea level rise encompasses only the last around 100-odd years [*]. Those observations are inconsistent with the notion that the polar ice sheets are out of equilibrium with the glacial-interglacial forcing of 12ky ago, to an extent that has real world significance, at last with respect to mass balance and sea level rise. [*] Pirazzoli PA (2005) A review of possible eustatic, isostatic and tectonic contributions in eight late-Holocene relative sea-level histories from the Mediterranean area Quart. Sci. Rev. 24, 1989-2001

        “Finally, several data from tectonic and non-tectonic areas are consistent with nearly stable global eustasy since 6000BP, thus challenging the assertion of significant additional melting of Antarctica after the complete melting of the former Northern Hemisphere ice caps “

        Lambeck K (2005) Sea level in Roman time in the Central Mediterranean and implications for recent change Earth Planet. Sci. Lett. 224, 563-575

        “Part of this change is the result of ongoing glacio-hydro isostatic adjustment of the crust subsequent to the last deglaciation. When corrected for this, using geologically constrained model predictions, the change in eustatic sea level since the Roman Period is -0.13 +/- 0.09 m. A comparison with tide-gauge records from nearby locations and with geologically constrained model predictions of the glacio-isostatic contributions establishes that the onset of modem sea-level rise occurred in recent time at similar to 100 +/- 53 years before present.”

        Church JA et al. (2008) Understanding global sea levels: past, present and future Sustainability Sci. 3, 9-22

        “While sea levels have varied by over 120 m during glacial/interglacial cycles, there has been little net rise over the past several millennia until the 19th century and early 20th century, when geological and tide-gauge data indicate an increase in the rate of sea-level rise.”

        Milne GA (2009) Identifying the causes of sea-level change Nature Geosci. 2, 471-478

        ”The observed fall in sea level following the end of major melting (~7,000 yr bp; Fig. 3b) is due to isostatic processes52. A growing number of high-resolution records (Fig. 3c) detect an acceleration in sea level around AD 1850–1900 (refs 43–45)”

        etc….
126581. shawnhet at 06:53 AM on 11 November 2009
        CO2 is not the only driver of climate
        Gord, "Your A-B-C left out the only energy source, the SUN. If A, B or C has more energy being radiated than the Sun provides then energy was CREATED....PERIOD." Gord, obviously, the sun is what warms the surface before IR radiation is emitted in A. I have not created energy by adding GH gases, I have changed how and where that energy is emitted to space, that combined with the fact that Earth has a lapse rate is what causes the surface to be warmer, not the creation of energy. IAC, there is no point continuing to argue this point, so I will pose some simple questions here: do you think it is possible to vary the emissivity of the atmosphere by varying GH gases? Assuming arguendo that this can happen, what would be the consequences IYO? Would any part of the atmosphere be heated? If so, which parts? Cheers, :)
126582. NewYorkJ at 06:51 AM on 11 November 2009
        Skeptical Science housekeeping: Comments Policy
        Seems like a welcome change, although those likely to break certain rules, such as ranting about one-world government or scientific conspiracy, are the ones likely to view the action of their comments being deleted as supporting their conspiracy theory. Warmists stifle dissent and won't debate!
        Response: To be honest, I've gotten to the point where I don't really care what conspiracy theorists think. You can never have a good faith discussion with them as they will dismiss any data that contradicts their position as the product of conspiracies. Removing that kind of attitude can only improve the signal to noise ratio.
126583. Mizimi at 03:23 AM on 11 November 2009
        An overview of Greenland ice trends
        "It is important to note, however, that the ice sheets are also still likely to be responding to changes in forcing at the end of the last glacial around 12 ka BP. As a consequence, they will be out of equilibrium with respect to the modern-day climate, and their reaction to external forcing is an integrated response to changes over multiple millennia." http://www.pages.unibe.ch/products/newsletters/2009-2/Special%20section/science%20highlights/Bamber_2009-2(52-54).pdf A balanced 'quick' overview of both N & S ice sheets which is worth reading alongside "Why the Greenland & Antarctic ice sheets are not collapsing" http://icecap.us/images/uploads/OllierPaine-NoIceSheetCollapse-AIGNewsAug.2009.pdf
126584. Steve L at 03:17 AM on 11 November 2009
        Skeptical Science housekeeping: Comments Policy
        FWIW, I think it's fine to carry out the new policy on new threads, but I would that it is a disservice to retroactively apply changes to old threads. This is partly selfish on my part, because I would much rather that John work on new posts rather than spend time editing old ones. But I also think that old threads with bad comments can serve a function in that, for example, they can be pointed to in showing what not to do, they can be searched for information on who is debating (is somebody just wasting your time), they may serve as data for someone who wants to understand how the global warming "debate" occurs in public forums, terrible comments may have a nugget of something interesting in them, etc. Of course, John is free to do what he likes and I'm sure I'll keep coming back regardless. RSVP -- I think you are referring to the list of the hottest arguments. I don't think that's a ranking of the quality of the arguments; I believe it's a ranking of how popular they are.
        Response: My priority is still and always will be writing new posts. Culling dodgy old comments is more like a leisure activity - something I do in an idle moment. Sometimes there'll be an off-topic comment that merely repeats common skeptic arguments - I sometimes use those as a teachable moment, linking to the appropriate page that debunks the skeptic argument. I mainly delete comments that contribute nothing to the discussion.
126585. Tom Dayton at 02:33 AM on 11 November 2009
        CO2 is not the only driver of climate
        Gord, you comment #221 did not answer my question in #218. I asked you whether you agree with just those two particular web pages, that the temperature of the Earth would be 255 K without an atmosphere--if nakedly exposed to the heat sink of outer space. Instead of answering, you ignored my request and commented on the remainder of the web pages on that site. It is difficult to discuss a chain of reasoning with you, if you won't discuss each link in the chain, one at a time. Let's see if we agree on that early link in the chain: Just those two web pages, please.
126586. chris at 01:38 AM on 11 November 2009
        Antarctica is gaining ice
        No problem SNRatio. I think we're probably about on the same wavelength, and I agree that we should be careful not to over-interpret observations that might be "contaminated" by artefacts of the measurement, or confounded by factors that we haven't fully considered. I'm glad you found that paper. As for the slow increase in Antarctic sea ice over the past few decades, I don't really have much insight into that. It seems somewhat counter-intuitive, but if the evidence is sufficiently strong that sea ice has grown somewhat while ocean and air temperatures have increased, then we may as well accept for now what the science says in relation to deep Southern ocean stratification and the effects of the ozone hole...although I guess in this case that there's more t be learned on this little piece of natural phenomena.
126587. Riccardo at 00:36 AM on 11 November 2009
        CO2 is not the only driver of climate
        Gord, i might say the same but it would bring us nowhere; I have a diffrent attitude. Here is where you wrote the correct net flux. There's the evironment temperature in it. This is what i was referring to and where your claims of violation of the second law of thermodynamics are wrong. You produced many posts but each and every time we pointed out the errors. You did not discuss any of them but repeated the acritical copy&paste ad infinitum. Really useless indeed. There's nothing to link on high school level physics, there is no doubt nor controversy on it. What is required is critical thinking, analisys, looking at the consequences. You're are surprised, i see, but that's just because you do not have much confidence with this basic physics.
126588. Alexandre at 23:35 PM on 10 November 2009
        Skeptical Science housekeeping: Comments Policy
        Even if RSVP comment is a very educated one, the practical effects of keeping civility among posters are usually very positive. The debate becomes deeper and less stressing. And, again in practical terms, the difference between science and politics or ideology is usually easily spotted.
126589. pdt at 23:05 PM on 10 November 2009
        Skeptical Science housekeeping: Comments Policy
        RSVP, I don't see how posting a link to a reference is suggesting that reference is irrefutable. Citing references is valuable in at least two ways. The first is to avoid repetition. The second is to give credit to someone's data, discovery, or thoughts.
126590. Henry Pool at 22:46 PM on 10 November 2009
        Skeptical Science housekeeping: Comments Policy
        I agree with everything by RSVP. If you delete too much and too quickly you will soon find yourself just talking to the people who already agree with you. What is the point about that?
        Response: No point at all. The last thing I want is an echo chamber. I'm deleting comments, not based on whether they agree with me or not, but based on behaviour. If you're rude, off-topic, repetitive, ideological or shouting, I'll delete your comment. My main priority is to have constructive, educational, readable and civil discussion threads.
        
        I've already started going through old discussion threads deleting what I deem inappropriate comments (this is not a big priority though, expect slow progress). This has included comments from both sides of the debate.
126591. RSVP at 22:36 PM on 10 November 2009
        Skeptical Science housekeeping: Comments Policy
        It is clear that personal attacks and ill mannered tone do nothing but weaken one's own position. That said, it can be just as damaging, if not more destructive, to ignore sound counterpoint and reasoning. This seems to happen quite often. What you refer to as "science" is a paradigm that has its origin in Greek philosophy some 3000 years ago. This trend started as a questioning of religion or myths that were originally in place to explain workings of the natural world. In those days, many arguments and even physical fights ensued as a result of disagreement. Socrates was sentenced to death. Much later, the Inquisition formalized this process, etc. Over time, certain branches of philosophy led to the hard sciences we now know as Physics and Chemistry, and given that philosophy included subjects that couldnt always be proven, the term Philosophy has become disparaged and in many circles, at worst, equated with esoterism. But this is normally due to an ignorance of what philosophy is and its relation to the origin of science. The point is, if you cannot take a philosophical approach to discovery and learning, your "science" is in danger of becoming a religion. We can make up whatever definitions we like, but there is a big difference between scientific laws and theories (that are based on observation), and theories that leave the scientific community searching ad infinitum for observations to substantiate specific theories, and we all know which ones these are. Given that the name and stated charter of this website implies the opportunity for skepticism about science (or perhaps more precisely "science in progress"), it is generally inconsistent and circular to be countering critique with hyperlinks to irrefutable sources. What is the point of opening a forum for discussion if the irrefutable source has already established so well all there is to say? And where is the room for being skeptical? And where is the recognition for any counterpoint? The only scale that is provided is one that orders arguments from being bad to worst. How exactly does that demonstrate objectivity?
        Response: The original 'charter' of this website was "getting skeptical about global warming skepticism". I have since taken a slightly different approach upon clarifying in my own mind the difference between "scientific skepticism" and "global warming skepticism". The approach of scientific skepticism is, as I see it, to avoid drawing any conclusions until you've reviewed all the data. Global warming skepticism is, again as I see it, to decide on the conclusion then find any data or arguments that back up that conclusion. Global warming skepticism is the antithesis of genuine scientific skepticism.
        
        What is the most common technique in global warming skepticism? In all my research into the many skeptic arguments, I've noticed a common pattern of focusing on a narrow piece of the puzzle while neglecting the whole picture. So generally, my goal with Skeptical Science is to educate by giving the broader picture. Show what the data and research says. Once you've perused all the peer reviewed scientific literature, you see how focusing on a single piece can lead to erroneous conclusions.
        
        Re a scale from bad to worst, are you refering to the taxonomical categories? There's no value judgement on which of "It's not happening", "It's not us", etc are better or worse. They just are what they are. If anything, it's more a logical progression - kind of like the steps in breaking an addiction (admitting you have a problem, etc). Eg - first you have to admit there's a problem, then you have to admit you're causing the problem, then you have to admit the problem is serious.
126592. Gord at 22:14 PM on 10 November 2009
        CO2 is not the only driver of climate
        Riccardo -re:your post #224 Don't you remember my post to YOU on this subject? (see my post#150) Funny how I have produced so many, many posts on this and Riccardo can't seem to remember any of them? Funny how Riccardo can't seem to find ANY Physics links to back-up his "opinions"? Funny how Riccardo has not been able to answer the questions I asked him?
126593. Riccardo at 21:46 PM on 10 November 2009
        Skeptical Science housekeeping: Comments Policy
        Crying against supposed censorship when one is not able to follow a few simple rules unfortunately happens way too often. Clearly those people have no idea at all on what censorship is. One question to John Cook the nerd :) I agree with you that reading comments is often very instructive, but unfortunately there no way for readers to know about new comments on old posts. Could it be possible to show the latest comments on the main page? I noticed that many blog softwares have this functionality, it would be nice to implement it here.
        Response: I've been meaning to create an RSS feed for comments for a while - another on the to-do list :-) In the meantime, here is a webpage of the latest comments.
126594. Riccardo at 21:37 PM on 10 November 2009
        CO2 is not the only driver of climate
        I believe this discussion will continue forever untill Gord does not convince himself that the net flux from an object at Te in an environment at Ta is proportional to (Te^4 -Ta^4). Once he posted this relation but didn't grasp the meaning: the net flux depends on ambient temperature too. By the way, a similar concept also apply to heat conduction and heat convection, the heat flux depends on the temperature gradient for the former and on temperature difference for the latter. In no cases this imply that a cooler object warms a warmer, whch in fact do not happen; less cooling is not warming. Claiming that a dependence on a gradient of some sort violates physical laws would require do dismantel a good part of known physics.
126595. Gord at 11:15 AM on 10 November 2009
        CO2 is not the only driver of climate
        shawnhet - re:your post#222 Gee, I see that my post that you are responding to has been deleted. (Perhaps, John Cook could post why....are there more new censorship rules?) ---- Your A-B-C left out the only energy source, the SUN. If A, B or C has more energy being radiated than the Sun provides then energy was CREATED....PERIOD. ---- The "Greenhouse Effect" links state that Heat Energy is RADIATED by the colder atmosphere to a warmer Earth. In case you still don't understand, heat transfer by RADIATION is one of the three methods of Heat Transfer. Heat transfer "Heat transfer is the transition of thermal energy from a hotter object to a cooler object.." Radiation "Radiation is the transfer of heat energy through empty space." "No medium is necessary for radiation to occur, for it is transfered through electromagnetic waves.." (PS: I have not posted this link before) http://en.wikipedia.org/wiki/Heat_transfer Further, The Greenhouse Effect as described by the physical geography in my post#17 explains how longwave radiation from the colder atmosphere heats the ground. Did you not read it?
126596. shawnhet at 09:40 AM on 10 November 2009
        CO2 is not the only driver of climate
        Gord, ""Now, when we add more GH gases to the atmosphere, *the surface cannot radiate that heat as effectively* so in order to balance the incoming and outgoing energy higher levels of the atmosphere must radiate more energy than they would OTW. The only way the higher levels of the atmosphere can do this is by raising their temperature. However, given that the Earth has a lapse rate, *the only way for the temperature of the atmosphere to go up is for the temperature of the surface to go up higher than that of the atmosphere*." You have cause and effect reversed and you have CREATED energy. Just like the Microprocessor (Earth) and Heat Sink (atmosphere) cannot "ever" radiate more energy than it receives from the Power Supply (Sun), the Earth and Atmosphere cannot "ever" radiate more energy than it receives from Sun, the only energy source." No, I haven't created energy. The Earth's surface is not radiating all the energy it receives to space. Whenever this occurs, the surface must warm in response. The mechanics of the process involve the eventual heating of the atmosphere to a level where sufficient heat can be radiated to space. The sequence of causation is as follows A-B-C A. because the atmosphere absorbs IR energy and prevents all the heat from the surface from radiating to space B. the temperature of the upper atmosphere must increase but, in order, for the temperature of the upper atmosphere to increase. C.the temperature of the Earth's surface must also increase because the Earth has a lapse rate Nowhere does this involve the creation of energy, as any process that impedes radiation flow will cause warming. IAC, if you don't want to deal with the specifics of my POV, I don't have much to add. You can, of course, disagree with the idea that GH impede the flow of radiation to space, but it is contrary to the laws of science(as you put it ;) to pretend that a hypothetical system where radiation is impeded will not be warmer than one where it isn't or that this increase in warmth is a violation of conservation of energy. "They ALL have heat flowing from the Cold Atmosphere to a Warmer Earth!" No, they all have *radiation* flowing from the atmosphere to the warmer Earth as many others have pointed out. If you keep bringing up examples that don't have the same properties as the greenhouse system, you will not get very far in your argument. Cheers, :)
126597. hohum3001 at 09:29 AM on 10 November 2009
        Other planets are warming
        What if the two scenerios are NOT mutally exclusive? Let's supposed that their IS indeed some sort of phenonema heating planets independantly of human activity. Let's suppose that human activity is also warming the planet. What then?
        Response: If there was some phenomenon warming the solar system - a phenomenon which cannot be solar activity as the sun has shown no long term trend over the last 50 years (if anything a cooling trend) and cannot be cosmic radiation as cosmic rays have also shown no long term trend - if there was some other phenomenon not yet considered that is causing warming throughout the solar system, then that would pose several questions:

        1. Why are not all planets and moons showing warming?
        2. Why isn't the Earth showing more warming? We already know with high understanding the warming effect of CO2 and other greenhouse gases. This warming effect has been confirmed by direct observations. This warming effect is consistent with the amount of heat content observed. So any additional "solar system warming" should add to the warming we're already caused. Where is it?
126598. Gord at 08:28 AM on 10 November 2009
        CO2 is not the only driver of climate
        Tom Dayton -re:your post #218 Your link ignores the Fact that the Sun is the only energy source. (my very first Post#15 on this forum began with this and continued throughout all my other posts...did you somehow miss all those posts?) The Sun can and does produce all the energy required for the current Earth surface temperature. I have produced many, many examples including Physics links that prove this including many calculations that show that the addition of an atmosphere will cool the Earth, not warm it. The Earth and atmosphere are not energy sources and cannot create energy. Yet, your link has the Atmosphere causing Te to rise from 255K (the temp produced by the only energy source, the Sun) to 288K. Your link has the Atmosphere CREATING energy, an impossibility. Typical. Why don't you read what I have already posted instead of producing endless links that violate the The Law of Conservation of Energy? What purpose do you hope to achieve by posting links like the above? HINTS: - The Law of Conservation of Energy won't change and my answers won't change, no matter how links you produce that violate this and other fundamental Laws of Science. - Repetion is TEDIUS.
126599. Gord at 08:27 AM on 10 November 2009
        CO2 is not the only driver of climate
        Tom Dayton -re:your post #217 If you read my Post#216 AGAIN, you will see that I explain that all the radiation is ultimately transfered to cold space. HINT: Repetion is TEDIUS.
126600. chris at 06:32 AM on 10 November 2009
        High CO2 in the past, Part 2
        There's another interesting study that relates to John Cook's "UPDATE" and Steve's post #1. Here's a summary: (i) Basalts from tectonic activity (volcanic eruptions or flood basalts), are highly weatherable and so are efficient in removing CO2 from the atmosphere (on very long timescales). As indicated in the link in John's "UPDATE", the formation of the Himalayas, as the Indian subcontinent crashed (and still crashes) remorselessly into sub-Asia, isn't considered a factor in the cooling associated with CO2 reduction that gave rise to the first Antarctic continental ice in the early Oligocene about 33 million years ago. The Himalayas are large knappe-based granitic structures and granite doesn't weather efficiently. (ii) Basaltic weathering is efficient in warm, moist environments, and can be considered a sort of “Gaia”-ish means of temperature regulation on the very long timescale. A hot, moist world resulting from high greenhouse gas levels promotes weathering, with a consequent reduction of atmospheric CO2, that generally “outcompetes” the release of CO2 into the atmosphere from volcanoes. In a low CO2, cold, dryish world, weathering is inefficient, and volcanic release of CO2 out-competes weathering-induced “draw-down” of CO2 from the atmosphere, keeping the earth from getting very cold. (iii) A recent paper in PNAS [*] suggests that the maintenance of high CO2 during the Paleo-Eocene was a result of the crunching of the Indian sub-continent into sub-Asia, and the subduction of carbonate-loaded plate above the Thethys sea; the carbonates were converted back into CO2 which was released back into the atmosphere. Around 65 MYA the Deccan Traps were formed by a massive flood basalt event associated with the end-Cretaceous extinctions. (iv) As India squeezed-out the Tethys sea around 50 MYA, the CO2-“factory” came to an end, and was overtaken by enhanced weathering from the Deccan Traps as these moved into the warm, moist tropical humid belt. CO2 withdrawl from weathering began to outcompete tectonic release of CO2 into the atmosphere, and by around 33 MYA CO2 levels had dropped to the threshold for polar continental ice sheet formation… [*] D. V. Kent and G. Muttoni (2008) Equatorial convergence of India and early Cenozoic climate trends PNAS 105:16065-16070 http://www.pnas.org/content/105/42/16065.abstract?sid=4e6a6e83-8034-4eef-b0a2-865623be72e1 I can’t find a downloadable version of Kent and Muttoni (2008). However there is a “Commentary” accompanying their article that summarises their proposal quite nicely: users.unimi.it/paleomag/geo2/Irving2008.pdf