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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Comments 110851 to 110900:

  1. CO2 has a short residence time
    Doug Mackie wrote: "The final amount of extra CO2 that remains in the atmosphere stays there on a time scale of centuries." This conclusion does not follow from the presented arguments. It could be true if the bulk atmosphere is a nearly isolated reservoir. It is not. Since the CO2 is considered as "well mixed" gas, it will mix well with the atmospheric boundary layer as well, the layer which supplies the estimated source of 200GT/y. Therefore, the relaxation time of CO2 perturbation must be still the same as the turnover time, 4-5 years. This estimation of characteristic time is consistent with global observations after Pinatubo eruption.
  2. Urban Heat Islands: serious problem or holiday destination for skeptics?
    david: The urban areas of the world only add up to a few percent of the earths surface. Farms, forest, wiild areas and ocean account the bulk of the surface. Careful measurement of urban effects show the effects of UHI are very small.
  3. Climate change: Water vapor makes for a wet argument
    Johnd, It is you who cannot read the chart. Incoming radiation from the sun=342 reflected (sun) radiation=107 outgoing longwave=235 reflected + outgoing longwave=incoming as required by physics. The energy radiated from the surface is a combination of energy from the sun and backradiation so it is larger than either. The chart is an accurate summary of the energy balance, if you know how to read it. No energy is counted twice. Some energy is lost from the surface by evaporation and convection. Read the chart more carefully before you try to explain it to others.
  4. Climate change: Water vapor makes for a wet argument
    michael sweet at 21:47 PM, it appears that some of your points are being made without reference to the chart. On the point of back radiation, the chart clearly shows that the back radiation value is 324 whilst the value of energy radiated off is 390, a deficit of 66. Any nett loss of energy is a cooling effect not a warming, it is dissipating into the atmosphere through radiation a portion of the energy transferred to the surface by solar radiation. Now remembering that thermal radiation is a transfer of heat energy, in this situation, if it is being lost from the surface through thermal radiation, then it is simply not available to be lost to the surface through evaporation. The processes in practice are vastly more complex than the chart indicates, however the energy cannot be assigned to two different processes simultaneously or accounted for twice when compiling the budget, which is what seems to be suggested.
  5. Plain english rebuttal to 'Global warming isn't happening' argument
    I, for one, am happy that the Fact that our world has been warming has at last been Found. Else all the Red Herrings of the sea would disappear like Deleted Comments are wont to do. The Yooper
  6. It's satellite microwave transmissions
    For what it's worth, I was shocked to hear such a ridiculous argument for global warming! In my not so humble opinion, this smacks of desperation on the part of the skeptics. Rather than explaining the science to a contrarian who came up with this argument, I would be more tempted to laugh. Bob Guercio
  7. Plain english rebuttal to 'Global warming isn't happening' argument
    James, good post. I agree with m. sweet's point, though. The inclusion of the stratosphere in #4 is confusing. I'd suggest dropping it from #4 and adding it as a parenthetical after the list, or as a footnote to #4. Also, I'd suggest dropping the comments about skeptics from #1, and put them with your discussion of the "bricks" at the end. If you do those two things, your list will be clean and uncluttered and pure evidence, and will serve to support your comments below. If you decide to take any of this editorial advice, feel free to delete this comment.
  8. Is climate science settled? Especially the important parts?
    First, why is anyone taking thingadonta seriously? Come on, people. Climate scientists are the equivalent of Aztec or Mayan priests sacrificing thousands of people? The goal of climate science is world domination? It's funny. Second, why didn't the moderator delete that post? It has zero science content, is off-topic, and entirely political. If it's real, it's evidence of a paranoid psychosis, and if it's fake, it's pure trolling. Either way, it has no place here.
  9. New presentation debunking Monckton's critique of IPCC predictions
    Roy #7, you've just done the same thing Monckton does... rewrite things to a false narrative which you can 'disprove'. The "refutation of Monckton" in the linked video and writeup is that he took a formula for "long term" warming for a given rise in CO2 and treated it as IMMEDIATE warming once that level of CO2 was reached. He calculated that an assumed level of CO2 at 2100 would result in the formula's warming result immediately in 2100 (thereby misapplying the formula) and then took a linear slope towards getting to that point over the past ten years (thereby ignoring that warming is predicted to be, and thus far has been, increasing in rate, rather than linear). The rest of your analysis is equally inaccurate, and if you are really going to argue that a seven year 'trend' means anything in the face of a hundred year trend in the opposite direction on either side of those seven years then this stops being about any kind of reason.
  10. Urban Heat Islands: serious problem or holiday destination for skeptics?
    uh, i'm no scientist, but if you have a world full of "urban heat islands", wouldn't that in itself warm the earth?
  11. Plain english rebuttal to 'Global warming isn't happening' argument
    VoxRat, the IPCC has a good explanation of choice of baseline in the Working Group I report from the TAR back in 2001. Sorry I've not got a more recent one; I'm lazy, and that popped up at the top of a Google search.
  12. Plain english rebuttal to 'Global warming isn't happening' argument
    "BTW, what exactly did you mean with your use of the word "halcyon"?" Sorry. It was a flippant allusion to the notion that there was once a Golden Age, when the climate was what it's "supposed to be". And I understand the concept of "anomalies"; I'm just curious as to what the (arbitrarily chosen) baseline period is in each of these cases; whether it's the same in each; and if there's any particular reason for choosing one period over another. (And, BTW, I share your enthusiasm for this site as a great resource.)
  13. Hurricanes And Climate Change: Boy Is This Science Not Settled!
    gpwayne @ 42 - "As mentioned in the post, models predict a reduction in frequence but increase in energy. This will lead to greater landfall if correct." Is that true?. The graphic above, indicates the more intense hurricanes seem to have less likelihood of making landfall (well major land masses anyway). Granted, it's only "eyeballing" & I've only skimmed through a handful of papers so far.
    Moderator Response: [Graham] - check out the intermediate, the paper is referenced there. (As I understand it, the argument is that greater intensity will lead to increased duration, so more will make landfall before blowing themselves out).
  14. How we know an ice age isn't just around the corner
    GC @ 58 - "it is nonsense to suggest that CO2 is driving global temperatures over the periods of time covered by the ices cores." I agree with you. Cavemen, woolly mammoths and sabre tooth tigers did not drive SUV's and build industrial smokestacks. Given the limits of scientific certainty that is. No, back then, CO2 acted as a feedback, responding to the temperature change, caused by changes in the Earth's orbit -out gassing from the oceans as the Earth warmed thereby amplifying the warming effect, then being absorbed back into the oceans as the Earth cooled. This was all in the "argument" I referred you to earlier.
  15. Plain english rebuttal to 'Global warming isn't happening' argument
    Re: VoxRat (3) In any trend analysis one has to deal with noise in the datasets. In climate science, anomalies are used to reduce noise in the data, enabling better discernment of whether or not there is change in the data. See here. Reference baselines typically consists of periods of 30+ years for statistical robustness. BTW, what exactly did you mean with your use of the word "halcyon"? If you genuinely seek to improve your knowledge, or have knowledge you wish to share here, that is why John created this resource for all. As far as coffee, my preference is Papua New Guinea, fresh roasted and ground. Cheers, The Yooper
  16. How we know an ice age isn't just around the corner
    Dapplewater (#54), Thanks to much improved time resolution, the Vostok ice core studies convincingly demonstrate that temperatures lead atmospheric CO2 concentrations. It is nonsense to suggest that CO2 is driving global temperatures over the periods of time covered by the ices cores. However, the hypothesis that falling global temperatures are associated with increasing glaciation, falling sea levels, reduced precipitation, widespread arid conditions and falling CO2 concentrations looks plausible.
  17. How we know an ice age isn't just around the corner
    Daniel Bailey (#50), The link you site assumes that CO2 concentration in the atmosphere drives global temperature whereas the exact opposite is more plausible. Looking back hundreds of millions of years we still lack the time resolution to put this matter to rest once and for all. It seems likely that what is true for the last 700,000 years is also true for the earlier Ice Ages. See my response to Dapplewater.
  18. Plain english rebuttal to 'Global warming isn't happening' argument
    Most of those graphs are presented in terms of "anomalies"... I.e. deviations from some arbitrarily chosen reference period. Is it the same reference period for all of them? Is there some reason to pick one over another? My first reaction was "Oh! the ordinate value is rising! But it's not so bad, because it's only about as far above what it's 'supposed' to be, as it was below for a few decades!" (What can I say; I just got up and haven't had coffee.) But then I realized they all seem to be relative to a period somewhere around 1980, not some halcyon period when all was right with the world.
  19. Urban Heat Islands: serious problem or holiday destination for skeptics?
    I wouldn't read too much into a lack of response, kdkd. People go away on vacations, or they get busy and don't have time to follow up. There have definitely been times when I've posted things here but been too busy to follow the site for a week or so afterwards -- if people had posed a bunch of challenging questions to me they would have mostly gone unanswered.
  20. Hurricanes And Climate Change: Boy Is This Science Not Settled!
    An interesting graphic of 150 years of tropical storm tracks, clear to see which region gets hammered the most.
  21. Plain english rebuttal to 'Global warming isn't happening' argument
    I meant the stratosphere was the exception in that it wasn’t warming. I didn’t mean that it wasn’t consistent with AGW – which it certainly is.
  22. Quantifying the human contribution to global warming
    Thanks for the answer Chris. In a nutshell my view is "all climate is local". Here's one particular location where the seasonal variations were examined and could not be explained by a temperature-SVP link. http://journals.ametsoc.org/doi/abs/10.1175/JHM484.1 But your answer is that the WV feedback is controlled by the aggregate large scale dynamics in tropical convection. If I have that right, do you also add the likelihood of an increased tropical region size as the world gets warmer? Are there estimates for that? Also I can not see how an energy flow equilibrium can govern water vapor. The ocean temperature buffering means that it takes years for an increase in CO2 forcing to raise global average temperature without feedback. But water vapor feedback takes hours or days at the most. The time scales are off. Just for the record, there is no such thing as conservation of energy other than over the long run at the top of the atmosphere. When there is concentrated heat somewhere like we saw this summer, there is not lack of heat elsewhere to make up for it.
  23. Sea level rise: the broader picture
    KL @ 77 - This seems to be a recurring theme with you. You have done this to death on other blogs as well I see. So the repetition is all your doing. Yes, I agree, the media and skeptic beat up of the stolen e-mails was indeed a travesty, but global warming continues, despite the "current"uncertainties in the analysis of the global energy budget. As, for the missing heat, seems unlikely to me that's it's found it's way down in the deep ocean, so quickly (no known mechanism for starters) , more likely an "accounting" error, or errors. But sure is strange how it shows good agreement until about 2005. I am genuinely curious to see how this issue is resolved though.
  24. Sea level rise: the broader picture
    Ken #77 While you insist on bringing up old arguments, perhaps you can explain why you haven't been able to deal with people's rebuttals of such adequately, for example here. Also you have completely failed to ever acknowledge issues surrounding measurement error.
  25. Anne-Marie Blackburn at 21:53 PM on 5 September 2010
    How we know an ice age isn't just around the corner
    johnd, I still don't see the relevance of your point. Natural factors would probably have led to cooling. Yet global temperatures are increasing, most probably because of increased greenhouse gas concentrations. The rate of removal of these additional greenhouse gas emissions or seasonal variations in CO2 levels do not change the fact that an ice age is unlikely. Nor does the capacity to remove additional CO2. The analysis is based on past and current observations, not hypothetical scenarios.
  26. Climate change: Water vapor makes for a wet argument
    Johnd, If you don't read what the experts explain you don't understand the basics. The chart shows all the energy comes from the sun. Other sources of energy like volcanos and waste heat are negligable. The outgoing radiation equals the incoming radiation as required by conservation of energy. The increase in greenhouse gasses increases the back radiation. Increased back radiation increases surface temperature. Increased temperatures increases evaporation of water. When CO2 was lower the back radiation was lower and surface temperatures were lower. As temperature increases, humidity increases. This is a positive feedback, since water is a greenhouse gas. When do you expect solar radiation to cease? At night energy dissipates to space, during the day it accumulates. The chart shows the average for the whole day.
  27. Hurricanes And Climate Change: Boy Is This Science Not Settled!
    Thanks for all the comments. A few responses: HumanityRules: you were right - Holland and Landsea. Berényi Péter: As mentioned in the post, models predict a reduction in frequence but increase in energy. This will lead to greater landfall if correct. Dappledwater: nice one. David Horton: Thank you. I quite agree - it is strange how the burden has been shifted. More energy into a system must have an effect, and if the effect isn't the obvious one (or the slightly less obvious but logical PDI increase) it is encumbent on those promoting the disssent to validate it with data. Ned: so, to sum up then - nobody's got a bloody clue! :)
  28. Is climate science settled? Especially the important parts?
    thingadonta wrote : "Climate scientists are not going to fool skeptics with this possible recent revival of an old-age trick-denying and using uncertainty in the Earth's climate and weather as a means to social control. A completely opposite way of looking at it (the skeptical one, by the way), is that you should actually never 'cast aside' one's 'doubt of climate science'; such is the road to ideology, blind faith, and false certainty as a means to social power and control. The Aztecs and Mayans discovered it, and now 21str century ‘scientists’ have discovered it (but not the sceptical ones)." These are very skewed comments(politically and scientifically), which reveal a lot more about you and your beliefs than about global warming itself. Politically, you seem to see "social power and control" as an inherent desire of scientists and others involved with research into global warming. Apart from the "skeptics", of course - whoever they might be and however you define them, beyond your belief that anyone who doesn't like or accept global warming must, by default, be a skeptic. That would seem to include everyone from Monckton to Lindzen, and every position from 'It's all a UN, secret government conspiracy' to 'The Greenhouse theory is false' to 'Maybe the effects won't be quite so serious as some suggest'. All skeptics/skeptical but few worthy of being taken seriously. With regards to the science, you have no answers or rebuttal and can only denigrate and belittle what you define as 'scientists', who are, again, all those apart from the "skeptical" ones you like. Again, they are undefined by you and so, presumably, run the gamut from Gerlich/Tscheuschner to Singer to Lindzen. They you would no doubt call scientists without the qualifying quote marks; the rest you smear by association. I find that reprehensible and snide but you are somehow allowed to make such assertions without ever backing up your beliefs. Shameful but very revealing of your motivations, beliefs and lack of serious credibility.
  29. How we know an ice age isn't just around the corner
    Anne-Marie Blackburn at 19:20 PM, I agree, CO2 don't drop for no reason. Just as the seasonal variation doesn't vary for no reason either. The nett global variation is greater than the total estimated human emissions, and when measured regionally the annual variations can be up to about 50ppm, but more often around 20ppm, well in excess of human emission levels, so the capacity to absorb higher levels is available if the right conditions are in place. These variations whilst large by comparison to the human emissions are small compared to the total land and ocean emissions which are about 27 times human emissions. Thus only a very small variation in the natural processes is required to make a significant difference to the nett gain or loss of CO2 from the atmosphere.
  30. Plain english rebuttal to 'Global warming isn't happening' argument
    Good post. I like the summary of the bullet points. It is too bad you have to summarize so much interesting data. In number 4 why is the stratosphere an exception? The stratosphere is a separate part of the atmosphere than the troposphere. The troposphere is predicted to warm and the stratosphere is predicted to cool. Both have been measured and are warming/cooling as predicted.
  31. How we know an ice age isn't just around the corner
    GC @ 48 - "I see plenty of evidence to suggest that CO2 is not a major climate driver." I gotta disagree GC, the link between CO2 and global temperature goes back a long way. The last 400,000 years. 650, 000 years. 800,000 years. However if yours is a version of the CO2 lags temperature argument, see here Why does CO2 lag temperature? And it's only a forcing this time around, not a feedback, because of human greenhouse gas emissions.
  32. Is climate science settled? Especially the important parts?
    Thingadonta @8 Jacob Bronowksi was very clear in his conclusions about human history in his infamous 'Ascent of Man' series and book; if history teaches us anything, its that humans should never be too sure of themselves. Ahh, the truth is out - Climate change deniers are not human ! Perhaps they are alien beings from a hot planet planning to invade us... :-)
  33. Sea level rise: the broader picture
    DW #70 Before we get into repetition please have a look at this topic from May this year: http://www.skepticalscience.com/news.php?p=2&t=78&&n=202 Note my posts #24, #30, #60, #67 - particularly #67 I came across Dr Trenberth's paper as a result of the Climategate 'travesty' emails, and have a passing familiarity with it since late 2009. If 'the missing heat' is way down deep it got there very quickly by an unknown process DW, so don't hold your breath waiting for it to burst forth.
  34. Is climate science settled? Especially the important parts?
    @thingadonta #8 To summarize your viewpoint: you can never be sure about anything. Indeed. You can never be sure that tomorrow the laws of thermodynamics will still apply or that the sun will still rise in the east. Indeed. And you cannot eliminate this uncertainty by doing irrational things like sacrificing people. Indeed. You then suggest that this is the same as what climate scientists try to do: to take away the uncertainty with irrational hocus-pocus. That’s where you’re wrong. No science is ever completely settled. Science strives to minimize the uncertainty but a 100% certainty is not achievable. Nevertheless, in the past this hasn’t stopped us from using the laws of thermodynamics to construct cars and power plants, using the laws of electromagnetism to build cellphones, using the laws of mechanics to launch space ships. I never heard anyone demanding that the science should be settled for a 100% before using this knowledge. If we had waited, we would still be living in caves. Using the knowledge you have to your best advantage (taking into account the uncertainty that still exists) is not irrational. It is the best we can do. We don’t know absolutely everything about climate science. We know enough to act. That’s the message climate scientists try to get across.
  35. The surprising result when you compare bad weather stations to good stations
    michael sweet @ 65 Scientists have nothing to lose if they present real data limiting adjustments only to what needs adjusting to ensure we're comparing apples with apples. I would feel far more comfortable with data showing wider divergence between well and poorly sited stations. I have no investment in the direction of the divergences. For example, if poorly sited stations in some (or even many) instances showed cooler trends (a counterintuitive result given the assumptions underpinning the surface stations project), I would happily accept this. I have no problem with all the data showing a warming trend. However, the data are so exquisitely consistent over extended periods as to seem improbable and thus implausible. Data measurement is never so utterly robust as to yield zero anomalies between a range of measurements over many years. I would liken the outcome to tossing and coin and finding it lands neither heads nor tails but stood vertically on its rim - an improbable but nevertheless possible outcome. As I've pointed out before, I may have misunderstood the derivation of the data set and if so would be very happy to stand corrected. Part of the problem lies with what I suspect is your assumption that I have raised the issue in order to push a sceptical agenda.
  36. How we know an ice age isn't just around the corner
    JohnD, You know what the natural processes are that remove CO2 from the atmosphere. You even commented on it. As the post makes clear, ocean uptake of CO2 has profound consequences of its own; natural processes are not necessarily benign. Nor is it guaranteed to continue as it has done in the past
  37. Is climate science settled? Especially the important parts?
    jbowers: you nailed the deniers position very well: the science isn't settled, unless it's their science.
  38. Anne-Marie Blackburn at 19:20 PM on 5 September 2010
    How we know an ice age isn't just around the corner
    johnd, you would need evidence that in the absence of human emissions of CO2 natural processes would be removing 2ppm CO2. Before the Industrial Revolution, the system was more or less at equilibrium - natural processes weren't removing more CO2 than they were emitting. They are now only removing half of the additional CO2 humans are emitting, i.e. the CO2 which has disrupted the equilibrium. So why would you think that CO2 would be removed at similar rate without human emissions? CO2 levels don't just drop for no reason - they are usually a feedback process.
  39. Quantifying the human contribution to global warming
    Chris Colose @ 21 - A Matter of Humidity Sherwood & Dessler 2009. "Thus, although there continues to be some uncertainty about its exact magnitude, the water vapor feedback is virtually certain to be strongly positive, with most evidence supporting a magnitude of 1.5 to 2.0 W/m2/K, sufficient to roughly double the warming that would otherwise occur. To date, observational records are too short to pin down the exact size of the water vapor feedback in response to long-term warming from anthropogenic greenhouse gases. However, it seems unlikely that the water vapor feedback in response to long-term warming would behave differently from that observed in response to shorter-time scale climate variations. There remain many uncertainties in our simulations of the climate, but evidence for the water vapor feedback—and the large future climate warming it implies—is now strong."
  40. Is climate science settled? Especially the important parts?
    Okay, see how the title says the science isn't settled, the plastic sceptics say the alarmists say it is settled, yet Monckton says it is settled as well... It's ironic. Maybe I should have been explicit about it, but I'd have thought my stating that I agree with MattJ would have helped you figure that one out. Try the link I posted to Citizen's Challenge.
  41. Is climate science settled? Especially the important parts?
    J Bowers I hope you are being fectitious, quoting Monckton. If not, are you questioning the validity of science agreed on by 97% of climate scientists and virtually every major scientific organization in the world, and then offering Monckton as proof they are all wrong? You must be kidding. I'm sure a journalist with no science background, who claims to have invented cures for all kinds of diseases, and who tells you the earth is cooling and then tells you, the warming is due to something other than greenhouse gases, and then tells you not to worry because global warming will be benficial, is a better source than all those scientists.
  42. New presentation debunking Monckton's critique of IPCC predictions
    Roy Latham @ 7 - "The trend for the last century is around the lower bound of the IPCC predictions." Doesn't make sense. The IPCC hasn't been around for a century.
  43. Climate change: Water vapor makes for a wet argument
    scaddenp at 14:39 PM, Phil, it is not really a critical path chart which would show the sequence of events, such a chart probably doesn't exist such is the complexity of the processes. However the question this chart immediately raises is that as evaporation requires an input of energy, how can IR radiation provide this. The chart shows a value of 390 for surface radiation and 324 for back radiation. Clearly there is a nett deficit of about 66 where an excess would required if energy was to be put into the evaporation process. From the chart it appears the process relies on incoming solar energy to provide the energy that not only drives the evaporation and other consumers of energy but to make up the nett loss in IR radiation. IR radiation can only enter the system after solar radiation has already transferred it's energy to the surface including the water that covers 2/3 of the surface. Immediately the solar radiation ceases, the losses of IR increase rapidly leaving even less energy to contribute to evaporation, even if there was excess available in the first place.
  44. New presentation debunking Monckton's critique of IPCC predictions
    The refutation of Monckton is, in essence, that the range of IPCC predictions is so broad as to include global warming so slight as to pose no serious problem, all the way to predictions that global warming is a dire problem. So when one wants to validate the IPCC one takes the data as being within the lower bound -- that global warming is not a problem -- validation. However, when one argues that global warming is a serious problem, one takes the midpoint or higher of the predictions. The trend for the last century is around the lower bound of the IPCC predictions. Skeptics argue that the relatively low rate of warming that started after the Little Ice Age was the trend likely to continue. That is denounced by crisis advocates as too low, but it is now supported as being within the range of model predictions. The refutation of Monckton asserts that nothing much can be said from seven years of data or even fifteen years. Why is that? Crisis advocates say that there is no solar activity going on, no ocean cycles, no paucity of volcanic activity -- that there is nothing to presently account for climate change other than CO2. Skeptics claim, by contrast, that climate is complex, with CO2 being one of many factors, and without all the factors being well modeled. Predictions that just about anything could happen supports the skeptics, not climate crisis.
  45. How we know an ice age isn't just around the corner
    scaddenp at 14:25 PM, I am looking for some explanation as to why it would not be so. Only about half of the current emissions are estimated to remain in the atmosphere, so the other half are being absorbed by natural processes which indicates that those processes are not that slow. In addition the seasonal fluctuations indicate that the capacity to absorb extra CO2 are in excess of the total anthropogenic emissions and further indicates that natural processes may have the capability of being a number of times faster.
  46. Climate change: Water vapor makes for a wet argument
    Johnd, firstly, forget clouds etc - you MEASURE the radiation coming from the atmosphere (not the sun), that is warming the sea. However you slice the cake, you have more radiation warming the sea with GHG than without them. And for equal windspeed, waves etc. warmer water will result in more evaporation than cooler water. The chart which shows all the energy interactions from from Trenberth & Kiehl. Latent heat etc. that you keep asking about. I would recommend the Science of Doom series Earth Energy Budget for the gory detail.
  47. How we know an ice age isn't just around the corner
    Re: Joe Blog (46) and GC (47) "Full-blown glaciation with high GHG level" A more robust discussion of this issue can be found here. The post, reader comments and the NOTES section give valuable insights on this. The Yooper
  48. How we know an ice age isn't just around the corner
    JohnD - are you under the impression that CO2 would be dropping by the amount it currently sequesters of current emissions even we were werent emitting? Net CO2 losses from natural processes is extremely slow and obviously completely overwhelmed by human emissions as CO2 is rising.
  49. Is climate science settled? Especially the important parts?
    Thingadonta, there is a qualitative difference between science and the "exploitation of uncertainties" you describe, and for once I'd like to see you actually admit that you're capable of learning (being a skeptic is pointless otherwise). It would make many here much more willing to be patient with you. In addition to what James Wight has said, understand that science--unlike any of the other practices you mentioned--is completely open about what it doesn't know. That is, in fact, the opposite of those historical 'exploitations'. The rich and powerful sought (and still seek) to control what is known and unknown by hiding their uncertainty behind a convenient "truth." Once truth is claimed, science has stopped. But you keep looking for certainty. I suggest you find a church, because you won't get it in science. You will, however, get people who are willing to act on a certain level of probability. There is a high probability that AGW is occurring. That probability, according to the people who have dedicated their lives to studying climate (and who definitely wish they were wrong, for a number of reasons), is much higher than any other scenario for the near future. Given the evidence, and looking at the math, I agree. Certainty in science doesn't mean the discovery of absolute truth; it means reaching the point of willingness to act. With climate change, I'm there. With C-section vs. natural birth for twins, I'm still not sure, and I only have a few months to figure it out and may not even then, but I'll be forced to act. Something tells me that even if we get 10 C warming in the next 20 years, you'll still be like, "It has to be something else. Couldn't possibly be AGW." I've asked this of others: what would be convincing evidence of AGW? What would it look like to you? Btw, you do manage to actually act, don't you? Even in the midst of the storm of uncertainty and doubt that is your life?
  50. Quantifying the human contribution to global warming
    Eric, this is a good question, and a lot of popular accounts of the water vapor feedback get this wrong. I'm trying to work on more posts on feedbacks on my own site and possibly for guest contributions to others to clarify such matters. First of all, C-C only provides an upper bound on the water vapor content in a given parcel of air at some temperature. It is therefore reasonable to assume that if the vapor pressure reaches or exceeds the saturation vapor pressure, you will get condensation. However, C-C does not, in itself, tell you how water vapor will change as the climate warms. Secondly, just because warmer air has a greater capacity to "hold" more water vapor, it is not at all self-evident that it will. It is like saying that a larger bucket will hold more water than a small one, neglecting how leaky either one of them is. However, if relative humidity (the percentage of vapor the air is actually holding relative to saturation) stays roughly constant, then the C-C relation is a great starting point for describing the fractional change in vapor content per unit warming (and like CO2, it's the fractional change rather than the absolute change which is important for the radiative transfer). And to the extent relative humidity is conserved in the large scale, as wasexpected going back to at least Manabe and Wetherald in the '60's water vapor must provide a strong positive feedback. There are solid energetic constraints for why relative humidity should remain roughly conserved in the lower atmosphere, but these arguments do not hold a lot of weight in the upper free atmosphere, and it is higher up where air is cold and where water vapor has the strongest contribution to feedback (the lower level air is more important though for precipitation responses). There are several physically plausible mechanisms for getting a negative water vapor feedback. The Held and Soden (2000) review paper on water vapor feedback provides some examples. Before the IRIS cloud hypothesis, Lindzen's idea in the early 1990's was that the mean detrainment altitude of deep convection will be both higher and cooler in a warmer climate. The water vapor deposited into the free atmosphere depends on the saturation vapor pressure at the temperature of cloud detrainment, and so this would in principle lead to less vapor left behind at higher altitudes. There is not really a theoretical basis (as far as I know) as to why this should be wrong, but like IRIS, there was really no supporting evidence for this. Many observational-based approaches and more sophisticated GCM's have evolved, and responses to ENSO, Pinatubo, and satellite observations show that models are pretty much getting things right. The Dessler and Sherwood paper in Science last year describes the evidence rather well. Furthermore, the developed thinking now is that the water vapor feedback is controlled by the large-scale dynamics and the saturation specific humidity in the outflow regions of tropical deep convective systems, and is not particularly sensitive to the detailed microphysics (e.g., Sherwood and Meyer 2006).

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