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Comments 118651 to 118700:

118651. PaulK at 19:12 PM on 29 May 2010
        There's no empirical evidence
        Hi Doug, Thanks for the kind words. Re your post #89, I am certainly not saying that the temperature and OHC measurements for the past 40 years are "wrong", although they do carry some hefty measurement uncertainties. We have undoubtedly seen planetary heating over a long timeframe. The key issue here, for me at least, is climate sensitivity and, ultimately, the cause and attribution of the heating. A careful reading of the Trenberth and Fusillo paper reveals that they do not claim anywhere that the satellite measurements of radiative imbalance match the climate models. On the contrary, they state that they do NOT, and then use the error statistics on the satellite measurements to show that the satellite data can be adjusted within the error bars so that it is “not incompatible with” the residual imbalance inferred from climate models. This however then leaves Trenberth’s question of where the missing heat energy was going in the period from around 2002 to 2008, when OHC showed a flat/cooling trend (Willis, Levitus, Cazenave). For me the jury is still out on OHC from the Schuckman paper, which is not only an outlier relative to the three papers I mention, and has not been reconciled to the shallower data, but would also mean that all previous reconciliations of energy balance (which did not account for Schuckman’s variation in deep ocean heat content) were fundamentally flawed. But back on topic, in practical terms the relative error statistics on the radiative imbalance from satellite measurements are very large (error analysis on the difference between two large numbers always reveals poor statistics); the measurement noise on the difference turns out to be almost an order of magnitude greater than the signal we are interested in! On the other hand satellite measurements for OLR can be quite PRECISE, but INACCURATE in absolute terms. This implies that the relative errors on trends in the measurements should be smaller than the error in absolute magnitude of the measurement, and very much smaller than the (even larger) relative error in the difference between the measurements. It is quite possible - likely even - that we can then deduce more from the trends in individual measurements than we can from the absolute differences between those measurements. So, is it important if a climate model (from a simple analytic model to a CGCM) doesn’t match the observed trends in OLR? Well, it obviously depends on what information one is trying to abstract from the model. But if one is talking about attribution studies, I happen to believe that it is crucially important.
118652. Doug Bostrom at 18:27 PM on 29 May 2010
        Latest GRACE data on Greenland ice mass
        Wes, on a general note it's helpful to remember that IPCC is conservative in its assessments and of course all research cited in the IPCC 2007 reports is a minimum of 4 years old at this point. More recent research in fact indicates an acceleration of the wasting process in Greenland. That's why what you see reported on sites such as SkS may appear different than the 4th IPCC assessment. As an exercise, you might compare the 3rd report w/the 4th.
118653. wes george at 18:18 PM on 29 May 2010
        Latest GRACE data on Greenland ice mass
        "The latest research indicates roughly 1 to 2 metres sea level rise by 2100 ..." Well, I guess that's more likely than a total melt by 2065 for a 7 metre rise, something that was once suggested here as an admittedly remote possibility once. Still, the IPCC models projected for even the worst possible scenario shows less than 50cm sea level rise by 2100 and only 100cm rise by 2200 and that's the worst case scenario...perhaps more likely 20 to 30cm by 2100. Big margin there. 2 metre rise scenario isn't until 2330 or so. So, I guess your interpretation of the latest data disagrees with the IPCC worst possible scenario by a factor of 2 to 4? http://www.grida.no/publications/other/ipcc%5Ftar/?src=/climate/ipcc_tar/wg1/fig11-16.htm
118654. wes george at 18:00 PM on 29 May 2010
        Latest GRACE data on Greenland ice mass
        Marcus, Unfounded myth? There are Viking graves that are still permafrost today. The graves weren't dug in permafrost. [Let's stay in the correct hemisphere for this topic.]
118655. RSVP at 17:50 PM on 29 May 2010
        On temperature and CO2 in the past
        Riccardo, Very interesting. The top two graphs are quite telling. The first suggesting CO2 increases with warming, while the second clearly indicates a deviation from this natural locus due to man's excessive fossil fuel combustion.
118656. Doug Bostrom at 17:27 PM on 29 May 2010
        On temperature and CO2 in the past
        Figure 2 is a pretty stunning visualization. "Thought provoking", as Ned understates. Thank you, Riccardo.
118657. Riccardo at 16:36 PM on 29 May 2010
        On temperature and CO2 in the past
        Ned, you made my feelings explicit, thanks. Marcus, I was talking about geologists and, you know, they use a very slow clocks and would call instantaneous something that happens in a few thousand years. :)
118658. johnd at 14:27 PM on 29 May 2010
        Working out climate sensitivity from satellite measurements
        scaddenp at 13:33 PM, what on earth causes you to jump to that conclusion??? Read all the relevant posts.
118659. scaddenp at 13:33 PM on 29 May 2010
        Working out climate sensitivity from satellite measurements
        Johnd - what on earth gives you the idea that clouds are left out of the process in climate model? See chp8 for instance in IPCC WG1, (for instance fig 8.14 and associated text). You should also note the improvement of cloud uncertainties between TAR and AR4 models.
118660. Marcus at 13:28 PM on 29 May 2010
        Latest GRACE data on Greenland ice mass
        Wes George, I do wish people would stop repeating unfounded myths as fact. First of all: Like today, Greenland during the MWP has always been an extremely marginal region for human settlement. I've seen nothing in historical records or paleoclimatic data to suggest that Greenland has *ever* been warmer-during the last 12,000 years-than it is today. The name Greenland was just an attempt by Eric the Red to encourage colonists to move there-it was not supposed to be an honest indication of what the place was like (though it did, & still does, get quite green around the coast during Summer). As to the claims of temperatures more than 1-3 degrees warmer than today I say-cite your source! I've looked at numerous reconstructions, dating back as far as the end of the last glacial period, & the only time period that was apparently warmer than today was the so-called Climatic Optimum-around 12,000 to 8,000 years BP. Temperatures then were around 0.3 to 0.4 degrees warmer than the 20th C average (depending on which reconstruction you look at), but occurred over a period of *centuries*, not decades as is occurring now. Maybe the Mediterranean region was 3 degrees warmer during the Minoan period, than the *global* average today-but that's a purely *local* phenomenon & has no bearing on what global temperatures were like at that time (indeed, IIRC, much of North America & Northern Europe was very cold at this point in history-due to a slowdown in the Gulf Stream).
118661. Jeff Freymueller at 13:15 PM on 29 May 2010
        Why Greenland's ice loss matters
        #57, that's OK, Ned. You reminded me that I need to look up that paper, and your explanation was fine!
118662. Jeff Freymueller at 13:11 PM on 29 May 2010
        Why Greenland's ice loss matters
        #49 Chris G, the coast is uplifting quite rapidly today, although that is also very close to where the ice is being lost right now. If/when the main area of ice loss shifts to the interior, the uplift will be highest there but still probably faster than sea level rise at the coast.
118663. Jeff Freymueller at 13:08 PM on 29 May 2010
        Latest GRACE data on Greenland ice mass
        #15 daisym, Greenland will rise faster than sea level rise if it continues to lose mass rapidly. This is currently happening in Alaska and Patagonia, where uplift due to rapid ice loss is several times faster than sea level rise. However, outside of the areas that are losing ice, land level won't change much and most of the world will just experience sea level rise.
118664. Marcus at 12:39 PM on 29 May 2010
        On temperature and CO2 in the past
        Hm, I sometimes have problems with the definition of a "Wild Swing" in temperature. Having looked at the Vostok Ice Cores extensively, we're seeing a delta T of 10 to 12 degrees C-which is very large-but over a space of 25 to 50 kyrs. To put that into a modern-day perspective, its an average rise of about +0.005 degrees per decade. The modern day warming has been at a rate of +0.1 degrees per decade!
118665. Ned at 12:06 PM on 29 May 2010
        On temperature and CO2 in the past
        Hey, Riccardo, thanks for a really neat post. Fig 2 and Fig 3 are really thought-provoking. Chris, your comments are as always very informative.
118666. Ned at 12:03 PM on 29 May 2010
        Why Greenland's ice loss matters
        Our esteemed host, John Cook, writes: Response: While you're at it, check out my blog post on this paper :-) Ooh, now I'm covered in embarrassment. I should have known John would have done a post about that paper (and I should have used the Search box to find it!) By all means, do check out John's blog post about the components of the mass balance budget for Greenland. He shows the exact same figures I put in the comment above, but he explains them better!
118667. johnd at 11:15 AM on 29 May 2010
        Working out climate sensitivity from satellite measurements
        chris at 08:24 AM, I would not have classed noise as a process. Can you define noise as it would apply to your considering it a process. Clouds would have to be the most obvious process that governs climate on both short and longer term timeframes, I'm surprised you didn't include them. Are they part of what you left aside as seasonal influences on local climate? If so, that would be neglecting that whilst local conditions may vary from clear to overcast, globally the amount of coverage could vary roughly in the range of 1/3 to 2/3 coverage at any one time, not only providing significant influence, but significant variation over both short and longer timeframes. Clouds are acknowledged as being the least understood of all climate factors, but that is not sufficient reason for them not to be included or ignored at any point of the process of climate study.
118668. shawnhet at 10:54 AM on 29 May 2010
        Working out climate sensitivity from satellite measurements
        "It's really uninteresting to conjecture upon ill-defined observations of unknown significance shawnhet. If Spencer and Braswell don't know what their linear striations relate to, I'm not very interested in speculating. You'd really have to know what the relationship actually is before considering what it might mean if it was "robust"! There is lots of interesting science on the relationships between TOA radiation variation and surface temperature luctuatins (see the papers cited in my post just above), and I've found this really interesting to read. Spencer and Braswell not so much..." Frankly, Chris, I don't know how you can intelligently comment on S&B if you don't understand what the linear striations mean. It is pretty clear that they relate to coefficient of the short-term feedback process that seems to operate on changes in radiative forcing. "What processes do (I) think governs the climate *on the timeframe* Spencer is dealing with? Noise, surely. What else governs climate on the monthly timescale (other than massive volcanic eruptions and extraterrestrial impacts). That's leaving aside seasonal influences on local climate obviously..." Noise alone won't work because it can't explain the existence of the linear striations in the data. Cheers, :)
118669. chris at 09:42 AM on 29 May 2010
        On temperature and CO2 in the past
        FerdiEgb at 08:09 AM on 29 May, 2010 That's problematic on a number of levels Ferdi. Firstly, one can't really analyze the temperature/CO2 relationships through the glacial cycles by simple inspection (other than perhaps assessing temporal lags and the relationships at points at the start and end of transitions where the system has found a new "equilibrium"). Otherwise one really needs to address these questions by modelling. More specifically to your point about Eamian temperature/[CO2] relationships, one needs to be careful in addressing this in relation to what we know. The temperature fell very slowly due to Milankovitch effects as we know. That's what dominated these fascinating phenomena. The [CO2] changes were purely feedbacks and relatively small (it's easy to determine that the contribution from [CO2] change of ~ 270-230 ppm, to the 4-6 oC globally averaged temperature change during the period you're describing, was around 0.7 oC within a climate sensitivity of 3 oC - it might have been somewhat more if very slow feedbacks enhanced the Charney sensitivity during these long transitions). But these feedback effects are "mixed in" with the Milankovitch-induced changes and simple inspection of graphs doesn't really allow these to be deconvoluted visually. We should also remember that once [CO2] gets into the atmosphere it can take a long time for levels to drop (e.g. Archer and Brovkin 2008). Your statement: "neither in recent times (Law Dome, Mauna Loa), neither in long past times (previous interglacials) there is much influence of CO2 on temperature visible.", is difficult to support in the light of the evidence. During the period (e.g. since mid 19th century) where we've got decent high resolution data from the Law Dome core, and excellent resolution from Mauna Loa, there is a very strong influence of [CO2] enhancement on temperature (around 0.8-0.9 oC's worth of temperature change!). Detailed analysis of attribution indicates that the dominant influence on surface temperature rise is the result of the massive ramping up of atmospheric [CO2] during this period. Likewise there is very stong evidence for a high [CO2]-temperature relationship throughout the entire Phanerozoic (see Detailed High CO2 in the past, Part 2, and papers cited in this post.
118670. Riccardo at 09:22 AM on 29 May 2010
        On temperature and CO2 in the past
        CoalGeologist, as i said at the end of the post, the study of past climate is done not to make analogies but to understand how our climate works. If we had to follow the fit in fig. 1, today's CO2 concentration would correspond to 11 °C which is way beyond any resonable estimate. But the problem is still there. Whatever initiated the warming or cooling in the past, whatever the feedback that kicked in, the climate system found its new state in a limited region of T and CO2. Today we're way out of that "natural" region and, at the very least, it's risky. FerdiEgb, what I showed here is not a detailed analisys of any particular event. On the contrary, I was looking at an overall picture as large as 800 Kyrs of just two variables, T and CO2. For sure it misses a lot of details. Tony O, the climate proved to be quite sensitive to small changes. Indeed geologists had hard times some decades ago before accepting that Milankovitch cycles were producing such wild swings. We already are beyond the limits, as Etkin 2010 shows, but we still have the right pedal at hand, the brakes.
118671. Doug Bostrom at 08:59 AM on 29 May 2010
        Collective Intelligence and climate change
        Thank you for doing the science, Carlo.
118672. s6carlo at 08:57 AM on 29 May 2010
        Collective Intelligence and climate change
        First of all thanks for the feedbacks about the Deliberatorium. @ Johnny Vector @ actually thoughtfull We know that arguments are poor in comparison with Skeptical Science or other web sites. It is an experiment and we don't pretend to insert all the knowledge on Climate Change in a single map, but on purpose is to show a new system that can be used to discuss this problem. The idea of collective intelligence is the collaboration among people, so in a future application we hope to build a map in a collaborative way, perhaps about a specific topic and not Climate Change in general. This experiment is to show how a discussion can be organized and if it is useful to understand people's sentiment. The tools can be used also to summarize a web sites as Skeptical Science and to build links among different articles, for example a map in which every post is linked to an external web page. In this case, the map will be useful to understand the relationship among articles. @NED Rate all the arguments takes a lot because even if they are not complete we tried to put the most important ideas about this problem. However, even if a user rate a small number of topic the data will be useful when used in an aggregate form. The user interface is very simple (or poor as you said) but I didn't think it was so confusing. The goal now is to understand if an argumentation map can be a good tool to discuss a problem, so we did not focused a lot in the interface, but probably you are right: even in this early stage the interface should be improved. Thanks, Carlo
118673. Tony O at 08:47 AM on 29 May 2010
        On temperature and CO2 in the past
        We have given the climate the biggest kick it has had in millions of years. Is it not likely that the climate will give the biggest fastest response in millions of years? It would seem inevitable that we will go beyond the "well defined limits". The evidence, that the Milankovich cycles plus the movement of the earths orbital plane through the solar plane have provided the timing of the Earth's glacial cycles, is overwhelming. Tiny changes in the energy reaching Earth have produced some massive climatic changes. The Milankovich cycles might be the trigger, but what was the bullet. We have given that trigger a mighty yank, we will undoubtedly do much learning over the next few decades.
118674. chris at 08:34 AM on 29 May 2010
        Robust warming of the global upper ocean
        Ken Lambert at 00:07 AM on 28 May, 2010

        "You might explain why there could be a "global short period where there hasn't been a significant radiative imbalance (e.g. due to a particular coincidence of atmospheric effects)". CO2GHG theorizes a relationship of forcing imbalance which is only dependent on log CO2 concentration. Is there any data to suggest a smothering of this CO2GHG forcing by increased cooling effects over a transient period which operates globally?"

        I don't think that's really correct Ken. If by "CO2GHG" you mean the Earth temperature response to enhanced [CO2], then this doesn't really "theorizes a relationship of forcing imbalance which is only dependent on log CO2 concentration". It "theorizes" that there is a contribution to forcing that depends on the logarithm of the proportion by which [CO2] changes. But it certainly doesn't presume that the forcing from enhanced greenhouse is the only contribution to forcing. It's obvious that that isn't the case. By considering the forcing from enhanced [CO2] we don't then decide to ignore all the other forcings (solar, atmsopheric aerosols, clouds etc.) that contribute to radiative forcing, and which modulate the effects of changes in [CO2]. So to answer your question, we know, for example that during the last 6-7 years there has been a steady reduction in the solar output which opposes the [CO2] forcing (not by much, but empirical analysis shows it is enough to effectively counter the expected increase in surface temperature from the [CO2] forcing during the solar downswing). We know that following large volcanic eruptions the forcing from [CO2] can be completely negated for a year or two. It's possible that a short term fluctuation in cloud cover (that might relate to ocean circulation fluctuations) could significantly modulate the [CO2]-induced radiative forcing for some period. Clearly there hasn't been large volcanic eruptions in recent years. I suspect that there likely hasn't been major variations in cloud cover either (we could investigate this, but I expect it would have been reported by now). We know that the solar effect is applicable to the period in question. The point is that our understanding of the radiative response to enhanced [CO2] doesn't require that there is some absolutely constant radiaive imbalance at the top of the atmosphere. It fluctuates up and down stochastically and in response to non-stochastic variation (like that incolving the solar cycle). Averaged over longish periods the stochastic variability averages out and the average forcing will apply. Strictly speaking, the theory of greenhouse gas forcing relates to the effects on Earth surface temperature once the latter has come to equilibrium with the forcing. The temporal trajectory by which it get's there is a different kettle of fish altogether, and periods of apparent temperature stasis or cooling, apparent slowdowns in sea level changes and ocean heat uptake, etc. aren't unexpected.
118675. chris at 08:24 AM on 29 May 2010
        Working out climate sensitivity from satellite measurements
        shawnhet at 08:04 AM on 29 May, 2010 It's really uninteresting to conjecture upon ill-defined observations of unknown significance shawnhet. If Spencer and Braswell don't know what their linear striations relate to, I'm not very interested in speculating. You'd really have to know what the relationship actually is before considering what it might mean if it was "robust"! There is lots of interesting science on the relationships between TOA radiation variation and surface temperature luctuatins (see the papers cited in my post just above), and I've found this really interesting to read. Spencer and Braswell not so much... What processes do (I) think governs the climate *on the timeframe* Spencer is dealing with? Noise, surely. What else governs climate on the monthly timescale (other than massive volcanic eruptions and extraterrestrial impacts). That's leaving aside seasonal influences on local climate obviously... What predictions can be made about the short term effects of forcing? Well I would say that there is good evidence that the water vapour responds in the direction of a positive feedback as has been determined empirically in several studies, on both short and long time scales. Of course it depends on the strength of the change in forcing. A large volcanic eruption or an extraterrestrial impact can have a dramatic short term effect! It also depends on what you mean by "short term".
118676. daisym at 08:17 AM on 29 May 2010
        Latest GRACE data on Greenland ice mass
        It has been said that, as Greenland ice melts, the landmass (relieved of this weight) will rise. If this is so, it should have an offsetting effect to the rising sea levels due to ice melt. If this is so, will the effect largely offset sea level rise from the melt water, or will it be insignificant?
        Response: The rising land is sharpest in regions where ice sheets are melting and yes, will offset sea level rise to some degree (perhaps even exceed it in some places). The effect is much less in other parts of the world. So as I explain in Greenland rising faster as ice loss accelerates, unless you have a huge melting ice sheet in your neighbourhood, you're unlikely to see uplift rates like those seen in Greenland.
118677. FerdiEgb at 08:09 AM on 29 May 2010
        On temperature and CO2 in the past
        I would post a similar comment as CoalGeologist: The influence of temperature on CO2 levels is quite linear: about 8 ppmv/K over the 420 kyr Vostok ice core period. The opposite is more problematic: neither in recent times (Law Dome, Mauna Loa), neither in long past times (previous interglacials) there is much influence of CO2 on temperature visible. In the previous interglacial (the Eemian), there was a huge overlap between temperature increase and CO2 increase, which makes it near impossible to know the two-way influences. But the end of the Eemian is quite interesting: the temperature (and CH4 levels) were decreasing until a new minimum, while CO2 levels remained high (for unknown reasons). After that, CO2 started to drop about 40 ppmv, but that had no measurable influence on temperature, nor ice sheet formation. Which points to a low influence of CO2 (including fast and slow feedbacks) on temperature. See here
118678. shawnhet at 08:04 AM on 29 May 2010
        Working out climate sensitivity from satellite measurements
        Chris, you did not really address my point above so to reiterate, Spencer and Braswell have detected (in their opinion) a short-term relationship btw changes in forcing and changes in temperature. If that relationship turns out to be robust, then the climate sensitivity will be less than, for instance, a system where the short-term response is governed by some other process. What processes do you think governs the climate *on the timeframe* Spencer is dealing with? What predictions can be made about the short term effects of changes in forcing? Cheers, :)
118679. johnd at 07:47 AM on 29 May 2010
        Working out climate sensitivity from satellite measurements
        regarding the comment in the OP on the ability to tweak results by choosing starting and finishing points, just by eyeballing the graph in the lead post, at least the points used by Lindzen et al 2009 (solid circles) start and finish at points that are close to the same value of SST anomaly, whereas Trenberth et al 2010 (open circles) do not. However as the period covered by both studies cover virtually one whole positive phase of the IPO just how relevant are either of them? Any such study should cover at least one full cycle of both phases, especially given the acknowledgement given to the ENSO influence, but unfortunately we will possibly have to wait a couple of decades at least before the next IPO negative phase passes under the watchful eye of the satellites.
118680. CoalGeologist at 07:46 AM on 29 May 2010
        On temperature and CO2 in the past
        My immediate impression looking at your top graph was that the residuals are not normally distributed around the regression line, especially at high values, and that a linear model might not be appropriate. Then, scrolling down, I saw the quadratic fit to similar data applied by Masson-Delmotte et al. 2010. I've posted previously about the potential risks of using past behavior as an analog for the present. I think it's worth noting that all the previous data points in your graph represent responses of the system interpreted to have been initiated by subtle changes in incoming solar radiation, related to Milankovitch cycles, which set off a complex sequence of feedbacks, partially involving CO₂. In the present circumstance, warming is being initiated by increasing CO₂, so it's not evident that the same feedback mechanism will prevail. Note that I'm not "saying", I'm asking, because I don't understand the behavior of the system sufficiently well to 'know' anything. Nevertheless, the non-linear trend of the data, together with the extreme departure from "natural" levels of CO₂, and the potential for slow feedback mechanism(s) that are not yet fully understood, could pose potentially serious consequences for future warming.
118681. chris at 07:15 AM on 29 May 2010
        Working out climate sensitivity from satellite measurements
        shawnhet at 05:30 AM on 29 May, 2010 If....if...if... I don't think so shawnhet. If you play around with the data sufficiently, eventually you might get something that seems to support the notion that you're trying to advance. Lindzen's conjuring up of a similar conclusion by cherrypicking convenient time points in analyzing TOA radiation in response to surface temperature variation is another example of this sort of numerology. There's a very interesting psychology going on here! The devotion that these celebrity crowdpleasers (e.g. Spencer and Lindzen) have in some circles is rather touching (if also a bit scary). Spencer's paper hasn't been published (I've read the in-press version on the AGU website), but already Berenyi Peter has referred to it twice on this site without having read it, and it's been publicised all over the web. Never mind that the two things that we can be fairly certain of in relation to Spencer's work are (i) there's a high probability that it will be wrong (he has a near 20-year record of getting things hopelessly wrong) and (ii) he will publicise overblown interpretations of his "analyses" on his blog and elsewhere. It can't be about science I think. After all if we want to understand the methodology, analyses, problems and interpretations of estimating fast feedbacks by regressing TOA net radiation variation in response to surface temperature fluctuations, there's quite a rich scientific literature. We can look at Tsushima et al 2005, Foster and Gregory 2006, Gregory and Foster, 2008, Murphy et al, 2010, Chung et al 2010, Trenberth 2010, and so on, to help us understand the science. But all that stuff is like lead balloons to those who need to have the issue filtered through some Lindzen/Spencer hokey. In fact Spencer's paper is not a big deal, and his conclusions are rather divorced from what he says on his website. He's fiddled around and found some linear striations. He doesn't know what they mean but observes that they're different from similar plots of random number series so they might have a physical basis. We can then put in place a train of "if's" as in your post. But it's much more satisfying to address the science rather than build castles in the air (at the top of the atmosphere?) based on conjecture...... ....if we had some ham we could make ham and eggs....if we had some eggs!
118682. FerdiEgb at 07:00 AM on 29 May 2010
        Why Greenland's ice loss matters
        Chris G at 01:27 AM on 29 May, 2010 About temperature: Besides simple pressure from the huge ice mass (over 3,000 m), air temperature and direct insolation are important, as whithout elevated temperature above freezing point (and summer melt at the ice surface), there wouldn't be any accelerating extra melt and/or smearing by water reaching the glacier bottom via moulins. There is a substantial difference in speed of the largest Greenland glacier between summer and winter (about 20%), but once the meltwater reaches the bottom, it stays there for longer periods, giving a sustained all-year acceleration of the glacier. See RealClimate on that topic.
118683. FerdiEgb at 06:30 AM on 29 May 2010
        Why Greenland's ice loss matters
        Peter Hogarth at 08:09 AM on 28 May, 2010 Thanks for the graphs! I used the raw (GISS) data, not corrected for anything, but as Greenland is only rural and had very few shifts in position of the thermometers, I didn't expect much difference. See the detailed trends here. The yearly average trends indeed are substantially increasing in the pre-1940 period, but I looked at the summer temperatures, as these are more important for the ice melt and these show hardly any trend. Thus it seems that mainly winters over Greenland (and the rest of the NH?) were colder some 100 years ago. About aerosols, see my previous comment...
118684. FerdiEgb at 06:10 AM on 29 May 2010
        Why Greenland's ice loss matters
        [That was an interesting post, had some intriguing parts. Why not try it again, without the insinuations such as Rahmstorf being "economical with the truth?"]
118685. Chris G at 05:43 AM on 29 May 2010
        Why Greenland's ice loss matters
        Thanks Ned, that's interesting stuff. I'm suffering from not wanting to buy a subscription to every worthy source, Science, Nature, AGU, etc., and determining which ones are most useful to me as a non-researcher. But, I'll see if I can't find an adequate way around that problem. I figured sublimation had to be small potatoes. If you are loosing a Lake Erie annually, well, that is a pretty high rate for sublimation to account for above and beyond whatever the historical baseline rate was. Besides, even if it were the primary mechanism for the loss, what would cause it to change that wasn't an effect of climate change?
118686. shawnhet at 05:30 AM on 29 May 2010
        Working out climate sensitivity from satellite measurements
        Chris, "Eventually they come up with "evidence of linear striations". These have slopes of around 6.2 W.m-2.K. Spencer and Braswell state: "These striations are significantly different from a similar plot of two time series of random numbers, shown in Fig. 3b, suggesting that the striations are due to some underlying physical process." Does that sound like they've "found low sensitivity here"? I don't think so. The paper has some interesting comparisons of a simplified model with GCM's. It's quite good at highlighting the difficulties of identifiying fast feedbacks in the presence of external forcinsg. What it doesn't present evidence of is "low sensitivity". " While S&B doesn't necessarily demonstrate low sensitivity, it is definitely consistent with *lower* sensitivity. If the short-term response to, for example, an increase forcing is a rapid warming followed by a reduction in temperature according to the pattern S&B found, then an increase in forcing will have a much smaller effect than if the response to forcing does not include such a short term response. If one assumes a given set of feedback where the short term response is consistent with Spencer's results one will have a less sensitive climate than if the short term response was consistent with the Stephan-Boltzmann relationship. Cheers, :)
118687. John Cross at 03:48 AM on 29 May 2010
        Websites to monitor the Arctic Sea Ice
        Great place to have all the links together. I can offer a little first hand knowledge on this topic since I was a navigation officer on ships that travelled in the Canadian arctic in the late 1970's and early 1980's. We always went about midway through July since the ice was thin enough to make it through then. Later on I will pull out some pictures of what the ice looked like in Hudson Straight and we can compare that to what it looks like this year. Best, John Cross
118688. Ned at 03:10 AM on 29 May 2010
        Latest GRACE data on Greenland ice mass
        Arjan writes: Though this graph looks worrisome, the grand question remains if the rate will continue (to accelerate). It's not well understood how ice sheets loose mass, and what mechanism has caused the more rapid mass loss. Over in one of the other Greenland threads I show some figures that break down the "Greenland ice loss" budget into its various components. The figures are from van den Broeke et al. 2009. And Doug is right that it's not really useful to say "Well, it would take a long time for the entire Greenland ice sheet to disappear." A loss of 10% of the ice would leave Greenland looking superficially more or less similar to its present appearance -- but it would add 65 cm to sea levels worldwide, which, combined with thermal expansion and contributions from Antarctica and mountain glaciers, would probably mean more than a meter of sea level rise. That's very problematic. You're right that the real question is if (or, more realistically, how much) the current loss of ice will accelerate over the next few decades. If global warming stopped now and the rate of loss stayed at a constant 200-300 GT/year, it would take a very long time to send 10% of that ice into the ocean. In the more probable case where the planet continues to warm and the rate of ice loss continues to accelerate, this could happen at the century time scale.
118689. Ned at 02:51 AM on 29 May 2010
        Why Greenland's ice loss matters
        Chris G writes: Thinking more about the rate of loss, it comes to mind that loss takes place through two mechanisms, flow of ice into the sea, and melting of ice and water flow into the sea. [...] The ice mass loss of Greenland is a total of these (and I suppose some evaporation/sublimation), and I don't think there are measurements that help attribute how the mass is being lost. Actually, people are starting to work on partitioning these. There's a 2009 Science paper by van den Broeke et al. that gets into this in some detail. The bottom line is, as they say "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. " More detail can be seen in some of the figures. The first figure shows a comparison of actual mass balance measurements from GRACE with their modeled ice budget (SMB - D, where SMB is modeled surface mass balance from a regional climate model, and D is measured discharge from marine-terminating outlet glaciers): The next figure from the paper breaks down the budget into surface mass balance and discharge: Clearly, discharge is increasing, and surface mass balance (precip minus runoff) is also increasingly negative, so both contribute to the overall negative mass balance. When this was all discussed a while ago, someone (Geo Guy?) was suggesting that sublimation could account for the loss of ice mass measured by GRACE. Here's a breakdown of the components of surface mass balance, including sublimation: Check out the paper if you're interested.
        Response: While you're at it, check out my blog post on this paper :-)
        
118690. Doug Bostrom at 02:25 AM on 29 May 2010
        Latest GRACE data on Greenland ice mass
        Arjan, though others seem fixated on the idea, the issue is not about whether or when Greenland's ice sheet will vanish.
118691. e at 02:04 AM on 29 May 2010
        The significance of the CO2 lag
        johnd, Yeah I think I was using the terms a little differently. In my usage and the equation quoted by others x was the feedback factor and f is the sum of all temperature changes and feedbacks. I'll try it with completely different terminology so it doesn't get confused with the others: In a geometric series, the sum (s) of infinite terms with a ratio (r) between successive terms and r < 1 can be calculated as follows: s = a / (1-r) Where a is the value of the first term (the initial forcing in our examples). This is where the 1/(1-x) equation comes from when we have an initial forcing of 1 degree. It calculates the net temperature change in the system after an initial forcing. In your example the final temperature was 1.23, so s=1.23. From the above equation, we can solve for r with: r = 1 - a/s, which is where I got 1-(1/1.23)=.187, which in your example is the ratio (r) between successive feedbacks in the system. This is the number that needs to be < 1 in order to have a finite net feedback. The point is to show that even if you have an infinite series of feedbacks on feedbacks, as long as the ratio of one feedback to the next is < 1, the net temperature change will not be infinite or "runaway".
118692. aj1983 at 01:48 AM on 29 May 2010
        Latest GRACE data on Greenland ice mass
        Though this graph looks worrisome, the grand question remains if the rate will continue (to accelerate). It's not well understood how ice sheets loose mass, and what mechanism has caused the more rapid mass loss. Glaciers have rapid advancements and retreats, and it might be that ice sheets have somewhat identical melting patterns. I wouldn't count on it though. Still, I believe currently it is thought that it will take thousands of years before (if) the Greenland ice sheet melts completely.
        Response: We don't need to depend on guess work on whether Greenland is going to continue to lose ice or whether its part of a natural cycle. A variety of studies based on empirical data show us that Greenland is highly sensitive to sustained warmer temperatures and hence we can expect sea level rise in the order of metres over the next few centuries.
        
        The main uncertainty to be resolved is time frame. The latest research indicates roughly 1 to 2 metres sea level rise by 2100 but it's difficult to say how quickly sea level rise will evolve after that. However, this uncertainty does not serve as a basis for inaction - quite the contrary.
        
118693. michael sweet at 01:46 AM on 29 May 2010
        Websites to monitor the Arctic Sea Ice
        Ned, I tried to keep a neutral tone when I wrote the post. The sea ice area has recovered a little from its 2007 low, but the ice volume has not come up at all. As you point out, both continue their long term declines. Of course, a reasonable person would not expect a monotonic decline for a parameter as complex as sea ice that depends on the weather.
118694. Chris G at 01:27 AM on 29 May 2010
        Why Greenland's ice loss matters
        I wouldn't think too much on temperature records over Greenland in determining melt rate. There is an awful lot of energy difference between water at 0C and ice at 0C; there's no difference in temperature.
118695. Chris G at 01:24 AM on 29 May 2010
        Why Greenland's ice loss matters
        Thinking more about the rate of loss, it comes to mind that loss takes place through two mechanisms, flow of ice into the sea, and melting of ice and water flow into the sea. The viscosity of ice and the topography of the land place some upper bounds on the rate of loss that way. I'm going to assume that the rate of melting places a lower bound on the loss than does the rate of flow of water. The ice mass loss of Greenland is a total of these (and I suppose some evaporation/sublimation), and I don't think there are measurements that help attribute how the mass is being lost. Just diving a little more into the potential problems of extrapolating the curve.
118696. Chris G at 01:13 AM on 29 May 2010
        Why Greenland's ice loss matters
        #46 Nichol, This factor is a subject of some arguments amongst the professionals. I've come across some articles on the subject; the ones I remember were looking more at Antarctic Peninsula glaciers and shelves rather than Greenland glaciers. Pine Island Glacier comes to mind. The impression I left with was that tides and storm surges were much larger effects, but every little bit adds up, and, as the ice thins through increased outflow, eventually a balance point is reached where small changes can matter. However, obviously, a spring tide in combination with a storm surge would dwarf any sea rise that is expected any time soon. Jeff F., I'm not sure that uplift will play much around the coast. I'm thinking that uplift will be greater where the mass loss is greater. Since the edges of the ice are inherently thinner than the interior, I'd suspect that there is greater potential for uplift in the interior. In the larger picture, I consider sea level rise to come in third, in terms of threat level, behind reductions in agricultural production as a result of changing patterns of temperature and precipitation, and behind problems associated the ocean acidification. Problems associated with sea level rise involve relocating people and the buildings they live and work in; the others lead to problems feeding all the people.
118697. sylas at 00:44 AM on 29 May 2010
        Has the greenhouse effect been falsified?
        Sorry I am a bit slow answering at present, I am not getting a lot of net time. Brényi Péter says:

        If you want to explain "greenhouse effect" anomaly due to changing carbon dioxide levels, you should provide some more details. Thanks.

        Actually, I do not want to explain the anomaly in the greenhouse effect, and I say so in the final paragraph of this blog post. This essay aims at a much more basic level: does the greenhouse effect exist at all? Most people do understand that there is a greenhouse effect. However, some people are skeptical even of this. The aim of this blog and this answer is to help people understand, at a very basic level and using direct observational data, simply that there really is an atmospheric greenhouse effect and that it really does give warmer temperatures at the surface than if the atmosphere did not have the greenhouse gases. All the diagrams shown, and your own comments, continue to confirm this basic point, so I presume we don't have a disagreement on this. The distinct question of the impact of changes in atmospheric composition on the magnitude of the greenhouse effect is dealt with as a separate issue in another page, which I have linked previously. However, I will just quickly respond to your comment about the effects of changing concentrations of carbon dioxide, since you may have missed the most important consequence, which is change to the width of the stopband. You say:

        It is easy to see that radiation temperature in CO2 stopband (between 14 and 16 μm) is about as cold as it can get. It means that photosphere (the region from where photons have a reasonable chance to escape to space) in this frequency band is above the troposphere. Below that line atmosphere is opaque (optically thick) in stopband. Now. In that region (lower stratosphere) temperature does not decrease with height anymore. If you put more carbon dioxide into air, photosphere will ascend, but its temperature may even increase slightly. Therefore OLR (Outgoing Longwave Radiation) should not diminish in this range with increasing CO2.

        The basic theory involved for calculating OLR is covered in some of the more technically detailed textbooks. In particular, Principles of Planetary Climate by Ray Pierrehumbert, due to be published by Cambridge Uni Press in Dec 2010 is excellent and designed to give the student all the tools to do the calculations themselves. This requires a computer to do a large numeric integration through all different frequencies and up a series of graduated steps in altitude of the atmosphere. But in the end you can calculate OLR for a given atmospheric profile. A major primary reference used for the effects of changing CO2 concentration is:

        • Myhre et al., (1998) New estimates of radiative forcing due to well mixed greenhouse gases, Geophysical Research Letters, Vol 25, No. 14, pp 2715-2718.

        This paper reports the original calculation of the approximately logarithmic effect of carbon dioxide, at about 5.35 W/m² per natural log. This is the impact on OLR for a given temperature. Of course, the consequence is that temperatures will increase until OLR again matches the solar absorption. What you are likely to find of particular interest is that this calculation reduced earlier calculations of the effect of increasing CO₂ by about 15%, because of more thorough consideration of all effects in particular in the stratosphere. The IPCC 2nd AR used about 6.3 W/m² per natural log CO₂. The IPPC 3rd AR and 4th AR used the improved value of 5.35, and this remains the best estimate for the approximately logarithmic relationship. I do not think there is any credible objection to this relation. If the optical depth at a given frequency is very small, or very large, then there is not much consequence for increasing concentrations for that frequency. Given a frequency in the stopband (with a large optical depth) emissions to space all come from high in the atmosphere, and doubling concentrations doesn't make much difference. Similarly, for a very low optical depth (transparency) the changes at that frequency are comparatively slight. The largest impact by far is for those frequencies where optical depth is close to unity. These are the frequencies for which additional concentrations move the effect of the atmosphere most strongly from being transparent to being opaque. Roughly speaking, higher concentrations mean the stopband is a little bit wider, stopping additional frequencies. This is the most important consequence of higher concentrations. The proof of that can be given in various ways. It can be done theoretically, as in calculations explained in Pierrehumber (2010) or reported in Myhre et al (1998). There are also observational confirmations of the enhanced greenhouse effect described in these pages at How do we know more CO2 is causing warming? I don't propose to go into a long further explanation here. There's ample description of the technical details in various references that have been given for people to chase up themselves if they have an interest, and the impact on OLR (the forcing) is taken for granted by major working scientists who happen to be skeptical of AGW, such as Lindzen or Christy. They tend to focus on the more reasonable question of response to forcings, or "climate sensitivity". Changes to atmospheric composition is, of course, a more technically complex question than I cover in this essay. That is deliberate. But I hope this brief account in the comments may go some way to answering your questions. Cheers -- sylas

118698. JSFarmer at 00:17 AM on 29 May 2010
        It's the sun
        Basic question- This topic addresses a skeptic's argument that sunspots have been increasing. The scientific rebuttal says the sun is cooling. Does sunspot activity = sun's temperature as the rebuttal implies?
        Response: "Does sunspot activity = sun's temperature as the rebuttal implies?"
        
        There's more to it than that. Solar activity is measured by more than just sunspots - we directly measure solar output using satellites. When the various satellite records are stitched together, they find a slight cooling trend over the satellite record. However, direct measurements only go back to 1978.
        
        So we use proxies to go further back. Sunspots go back to the early 1600s and are a good proxy for solar output. We can confirm this by comparing them to the direct satellite measurements when the two records overlap.
        
        Here's more info on how we measure solar activity...
        
118699. KR at 00:07 AM on 29 May 2010
        The significance of the CO2 lag
        Aaannnd - I write too quickly again. The formula should be Forcing/(1-Feedback). Note that negative feedback also goes into this formula: a negative feedback of 0.5 on a forcing of 1.0 results in a 0.6667 total rise; damping the effect. This is actually a fun exercise in Excel - build a column starting with the forcing and with each following (cell = previous cell * feedback). The sum of the forcing and feedback column gives the total feedback out to whatever number of rows you put in - I would suggest 30-40 or so. You can then compare that to "Forcing/(1-Feedback)".
118700. KR at 23:20 PM on 28 May 2010
        The significance of the CO2 lag
        johnd - A feedback gain of 'x', for example 0.5, means that a change in temperature of 1 degree C will through some mechanism (such as, say, increased H2O) cause an additional rise of 0.5 degree C. However, now there's an additional temperature change of 0.5, and the feedback on that is * 0.5 = 0.25 additional change, so you have an x^2 term, and so on and so on. Feedback operates on the temp. change, regardless of why it occurs; an initial forcing causes a shift, which causes a feedback, which causes a shift, which causes additional feedback, etc., resulting in the geometric series of 1+x+x^2+x^3+..., which sums to 1/(1-x) as long as -1 < x < 1. That's the stability criteria - each successive feedback is smaller, and there's a finite sum. So the total change from 1.0 degree C forcing, for a feedback of x=0.5, is 1 + 0.5 + 0.25 + 0.125 + 0.0625 + ... = 1/(1-0.5) = 2 degrees C. That's 1.0 in forcing and 1.0 in feedback. For a feedback of 0.25, the total is 1.333..., for a feedback of 0.75, a total of 4.0, and so on. You can Google positive and negative feedback for more details - there's quite a lot of well written stuff out there.

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