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Comments 118501 to 118550:

  1. Working out climate sensitivity from satellite measurements
    Here's a novice question (I'll even accept Dunning Kruger question). If the the temperature is increasing by about .18C per decade driven by a CO2 increase of about 19 ppm per decade or roughly 5%, dividing one by the other gives a climate sensitivity of 3.4C. If the climate is not in equilibrium and is catching up then it becomes more than 3.4C. Another way to look at it is if the CO2 has increased over the last century by about 33% and the temperature by about 1C then the sensitivity is 3C. Again the equilibrium clause holds and it becomes more than 3C. What's wrong with this elementary analysis?
  2. On temperature and CO2 in the past
    Thank you chris for anticipating me, you correctly got my point and explained it probably better than i could do. Marcel Bökstedt, adding to what chris said, the mechanism you described is in all respect the feedback operating between T and CO2 which there's no reason to think it's not operating now. But this alone can not reasonably tell you what the future temperature will be, and infact i did not quote any in my post. But just to try the impossible, i'll do some rather crude speculations now. (Remember, I'm not a climatologist so I can try weird things). If the local sensitivity in Antarctica is about 4 °C/(Wm-2) when considering just CO2 and CH4, you may want to add the ice albedo feedback which amounts roughly to the same forcing as CO2 and CH4 combined. The local sensitivity would then be 2 °C/Wm-2. To make it global we can use a polar amplification factor of about 2 (Masson-Delmotte et al. 2010). So my impossible estimate of the global climate sensitivity would have been 1 °C/Wm-2. HumanityRules, I'm not sure of what you mean by particular analisys. The Mauna Loa and Law Dome data are shown just to point out that today we are out of the natural regime in place for the last 800 Kyrs. The outcome definitely requires more knowledge than just the T and CO2 paleo data.
  3. Marcel Bökstedt at 21:37 PM on 29 May 2010
    On temperature and CO2 in the past
    chris> I absolutely agree with you on the antarctic amplification, thats why I stressed that T is the local temperature. By unreasonable simplification one could assume that the global temperature was determined by T in some simple way. I suppose that what I'm really worrying about is if this type of data give any real information about long term sensitivity. It seems to me that they sample data that are subject to a certain condition - no added carbon to the entire system - that simply isn't satified today.
  4. On temperature and CO2 in the past
    Marcel Bökstedt at 20:57 PM on 29 May, 2010 "As Riccardo points out in a comment, the first thing you think when you see figure 2 is that this means that no matter what we do from now on, we will eventually get a temperature increase of at least 11 degrees." Actually Marcel, Riccardo pointed out that todays levels of [CO2] would (in the context of the ice core data), require temperatures of around 11 oC in Antarctica in order to arise naturally by temperature-induced recruitment of CO2 from ocean and terrestrial stores. The real point of the data and its presentation is that we are way outside the regime where [CO2] levels are a result of natural phenomenon (the balance between CO2 release and sequestration, and temperature). The data say's little about the Earth surface temperature that will result when the Earth comes to equilibrium with the forcing resulting from 392 ppm (current [CO2]). That requires an understanding of climate sensitivity. The likely values are still centred around 3 oC of surface warming per doubling of [CO2] (with the possibility of a little bit higher sensitivity if very long term feedbacks are included). A more general point. The temperatures/temperature anomalies in the Figures (including HR's figure in post 11) are temperatures from proxies within the Antarctic cores. Due to polar amplification, the globally averaged temperature anomalies during these periods were smaller. So the full ~ 8 oC of temperature variation (glacial-interglacial-glacial) of around 8 oC corresponds to a globally averaged temperature change of 5-6 oC...
  5. Marcel Bökstedt at 20:57 PM on 29 May 2010
    On temperature and CO2 in the past
    Very interesting pictures. As Riccardo points out in a comment, the first thing you think when you see figure 2 is that this means that no matter what we do from now on, we will eventually get a temperature increase of at least 11 degrees. That's not good. But the situation is very complex, and a first look might be deceptive. There are many variables involved, and we are only keeping track of two - local temperature T and CO2 level C. Lets simplify and assume that local temperature is a good proxy for global temperature. There will be some the temperature forcings T' around (the one due to Mr. Milankovic and others). Then we have a suggested relationship between T and C. That is, we have a an equation f(C)=T, where f is an unknown function, which expresses approximately what temperature we would expect at a certain concentration of CO2. At the same time, we expect C and T to be largely determined by the forcing T', so that we actually have two functions T=t(T') and C=c(T'), related by the condition fc(T')=t(T'). Actually there are positive feedbacks between T and C. If one rises, so does the other. C can rise because there is a reservoir somewhere (in the oceans, in living stuff etc.) which contributes more CO2 to the atmosphere as the temperature goes up. Historically, the amount of carbon available in the atmosphere plus the carbon in the reservoir is a constant C', because at that time presumably no carbon was added to the system. Today we are changing C' by burning fossile coal. This means that at the same level of C, there will be more carbon left in the reservoir than before. It seems to me that this change of C' will change the feedbacks between T and C. But I don't know this for sure, correct me if I'm wrong! Maybe there is some sneaky way of constraining how these feedbacks depend on C'? So we would assume that today T and C depend on both T' and C'. We actually have T=t(C',T') and C=c(C',T'). If C' changes, we assume a new relation T=f(C',C), but I can't see how we can reconstruct the way T depends on C' from the paleo data, since C' didn't change before. There are no old data for varying levels of C'. The upshot seems to be that we don't really know if we will get the 11 degrees. From these pictures alone it could be 3 degrees or maybe 20. It depends on how the feedbacks between CO2 level and temperature react to an increase in the total amount of available carbon, and paleo data from the last half million years can't help us there.
  6. HumanityRules at 20:25 PM on 29 May 2010
    On temperature and CO2 in the past
    "what I showed here is not a detailed analisys of any particular event" It seems to me this isn't exactly true because the past 100 years is given very particular analysis by the presence of the Law Dome and Mauna Loa data. So the data that stands outside the green ellipse is generated in a very different way to the rest. I thought it's worth posting the Vostok record. Hopefully this version is accurate.
  7. HumanityRules at 19:58 PM on 29 May 2010
    Websites to monitor the Arctic Sea Ice
    10.John Cross Your pics would be great.
  8. Increasing CO2 has little to no effect
    I'm confused; where is the backscatter represented in this NASA energy budget representation of Earth? http://eosweb.larc.nasa.gov/EDDOCS/images/Erb/components2.gif Further to that the whole greenhouse gas theory is based on erroneous assumptions of the Earth system acting as a black body. Incorrect application of the Stephan-Boltzman constant in this case means that the entire theory is based on a basic undergraduate error. NASA discovered this at the time of the Apollo moon landings, when they discovered their assumptions on Moon surface temperatures by day and night were out by up to 60K - because a black body is a THEORETICAL two dimensional surface, there is no such comparison either with the surface of a planet/moon or the 3 dimensional gaseous atmosphere that surrounds it.. Therefore the entire reason we don't freeze is down to the dynamics of the entire atmosphere that surrounds us, not to trace gases. The charge that the second law of thermodynamics is broken by postulating that heat moves from colder atmosphere to warmer surface has never been satisfactorily answered. NASA know this and put in in plain sight in their energy budget diagram, nothing in that allows for any change in composition of minor components of the atmosphere causing large changes in the planetary heat budget - an increase in heat content just increases the convection and radiation components to maintain balance. The complexity of the climate system is caused by the latent heat content of the oceans, which transfer heat in timescales of hundreds and thousands of years due to the massive difference in their heat capacity. And finally the whole system is dependent on the only external energy source, the Sun. It is that, plus the interaction with the oceans on a millennial scale, that controls our planet's climate. For us to pretend we can contol this system by tweaking one trace gas like a thermostat is arrogance of the highest magnitude
  9. Latest GRACE data on Greenland ice mass
    wes, a superficial look at the papers may be misleading. The IPCC does not consider ice sheet melting at all. The 50 cm by 2100 are then, explicitly, a lower bound.
  10. 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.
  11. 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.
  12. 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
  13. 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.]
  14. 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.
  15. 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.
  16. 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. :)
  17. 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.
  18. 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.
  19. 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).
  20. 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!
  21. 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.
  22. 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.
  23. 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!
  24. 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.
  25. 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!
  26. 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.
  27. 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, :)
  28. 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.
  29. 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.
  30. Doug Bostrom at 08:59 AM on 29 May 2010
    Collective Intelligence and climate change
    Thank you for doing the science, Carlo.
  31. 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
  32. 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.
  33. 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.
  34. 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".
  35. 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.
  36. 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
  37. 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, :)
  38. 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.
  39. 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.
  40. 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!
  41. 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.
  42. 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...
  43. 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?"]
  44. 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?
  45. 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, :)
  46. 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
  47. 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.
  48. 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 :-)
  49. 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.
  50. 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".

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