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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 125851 to 125900:

  1. Predicting future sea level rise
    I guess that temperature could be replaced with energy in this article. The important issue being that with warming globe sea level rise will depend on where that energy is flowing (into sea/land ice, land, atmosphere, shallow or deep water etc). In your post "Understanding Trenberth's travesty" you reported on recent work to suggest that some of the energy is following into the deep ocean. My understanding is that old theories ignored deep oceans as an unimportant energy sink, being relatively stable. Energy into here, due to the higher pressures, has little affect on sea level. I was wondering whether is work is intergrated into estimates of sea-level rise. On a broader point Trenberth seemed unable to balance both the energy bugget and observed sea-level rise based on what we presently know. Suggesting there may be room for an unknown in the energy budget equation. I was wondering what impact that has on the work you present here. Trenberth's paper
    Response: The issue of heat being sequestered into the deep ocean has no bearing on the semi-empirical method. I'm not sure to what degree it will affect the kinematic study but the general sense I get from both papers is that thermal expansion becomes less of a contributing factor as time goes on. The newly released paper on the last interglacial (Kopp 2009) backs this up, finding ice sheets are vulnerable to sustained warm temperatures.

    Pfeffer 2008 is freely available online (you can register on Science for a free account) so I leave this one as an exercise for the reader :-)
  2. Is Pacific Decadal Oscillation the Smoking Gun?
    farwalker, to be honest, i do not have the will to go through the 55 pages of that (unpublished?) paper. But just from the first few pages you may realize that the whole reasoning is based on a faulty assumption: recovery from the LIA. What does it mean recovery? Is there any predefined climate state that have to be restored? Does it happen without any forcing? This argument would make even the skeptics crazy, they who love the sun so much! Indeed, there has been an increasing sun activity from the Maunder minimum but it has stopped about 60 years ago. The temperature increase from the mid 19th century up the the mid 20th century is surely due in part to the sun; but from then on it can not be the sun. Another faulty claim is that global warming has stopped in the last decade. There are good reason to believe that it's not cooling; and there's no way to support this claim based on temperature data. (Also here).
  3. Hockey sticks, 'unprecedented warming' and past climate change
    SNRatio, this is where it all started in #14: "Apropos sensitivity: Who is quite sure that a 3 deg sensitivity at the doubling from 140 to 280 ppm necessarily implies a 3 deg sensitivity at the next doubling, to 560 ppm? I'm not :-)" Here you are linking sensitivity and temperature. It's correct, they are by DT=lambda*DF. So the issue is wether the forcing is logarithmic or not. If it is, whenever CO2 concentration happens to double, you'll get 3 °C. Now, maybe I misunderstood your question. Are you asking if climate sensitivity can be assumed constant? Then in #20 you mention absorption band overlap. In my mind sensitivy is defined by the relation above. Then overlap has nothing to do with climate sensitivity but, eventually, with the forcing. This is the rationale of my comment #29. CO2 forcing does not depends on overlap, it's already considered. Maybe I misunderstood again or maybe we call sensitivity two different things. In #30 you explicitly say that "100 year sensitivity may be only about half of equilibrium sensitivity". This sensitivity can not be used to compare different time span or different situations; for example, even keeping everything else constant the next 100 years you'll get a lower "sensitivity", given that the process of reaching equilibrium is not linear. So, you can use this different definition of sensitivity just for inter-model comparison ot to compare them with reality in the very same situation and time span.
  4. Predicting future sea level rise
    Problem with this, and this goes to most PR/comms with the public from science (and is a big failure in engagement with the public by science) is that these numbers have zero immediacy with the public. I'm far from being a skeptic (I bled concern at heresysnowboarding.com/blog) but I look at 2050 and see anything from 20-60cm and I think, so what. What science needs to do is make it clear in terms of lost land (i.e. X%) or number of people displaced, amount of arable land lost etc etc. Putting up values of 4cm, 10cm etc doesn't mean much to fat, lazy, ignorant, unconcerned Western consumer...
  5. Predicting future sea level rise
    I just finished reading James Hansen's new book (Storms of my Granchildren) where he talks a lot about sea level rise and references a bunch of papers. Could you do a review and summary of Hansen's position vs. the other researchers in this area? Thanks.
  6. Is Pacific Decadal Oscillation the Smoking Gun?
    I think this is they correct place for this question, has anyone examined Akasofu's paper claiming that we are now in the cooling phase of the multi-decadal oscillation? http://people.iarc.uaf.edu/~sakasofu/pdf/two_natural_components_recent_climate_change.pdf Is there any merit to his arguments? It looks convincing but perhaps a little too neat.
  7. Climate's changed before
    Right; there are positive feedbacks, but they are not boundless. Water vapour can only be added into the atmosphere up to saturation point, counterbalanced by a tendency to rain more the more there is. Greenhouse gasses trapped under permafrost, ice, in the ocean and wherever else can only be released once, and there's only so much ice to melt to diminish Earth's reflectivity. One of the things that can counteract an excess of CO2 is excess growth/adaption of plants, and IIRC this is what eventually causes the atmosphere to bounce back and temperatures with it.
  8. Hockey sticks, 'unprecedented warming' and past climate change
    Batsvensson writes: "If CO2 can make the planet come out from an ice age isn't it also a plausible idea that CO2 can prevent the planet from entering an ice age as well? " As far as I understand it, there's a lot of disagreement as to the probable timing of the next glacial cycle in the absence of human intervention. Most people (but not all) now think that the current interglacial would have been longer than the Eemian (basically, cooling over the past millennia would have dipped towards the tipping point for initiation of a new glacial cycle, but probably not gotten cold enough). The next tipping point comes in ca. 50,000 years from now, when the Milankovich forcing almost certainly would be sufficient to start glaciation. Depending on how much CO2 we emit over the next 200 years, it's entirely possible that there will still be enough in the atmosphere to prevent the next glacial cycle from starting 50,000 years from now. That's a pretty astonishing thought, IMHO. See Clausen et al (2004), Did Humankind Prevent a Holocene Glaciation? Climatic Change, 69: 409-417. Not everyone agrees, however. I haven't discussed this with them, but my former colleagues Steve Vavrus and John Kutzbach have a paper out (coauthored with Bill Ruddiman) which allegedly confirms Ruddiman's hypothesis that we would already have started a glacial cycle if it weren't for the initiation of agriculture several millennia ago: Vavrus et al., 2008, "Climate model tests of the anthropogenic influence on greenhouse-induced climate change: the role of early human agriculture, industrialization, and vegetation feedbacks" Quaternary Science Reviews, 27: 1410-1425.
  9. Skeptical Science housekeeping: Twitter and double-posts
    pico writes: Lately I've been seeing 'skeptics' trotting out their lame argument that because there were vinyards in England during the Roman period, therefore global warming isn't happening. But you don't have that on your hottest skeptic arguments. Perhaps it is just too lame to add to your list, but it would be handy to be able to point them at a concise rebuttal. I like this rebuttal: Medieval warmth and English wine and a brief follow-up: English vinyards again To summarize: (1) Before 1200, there were at least 50 vinyards in England, all located south of a line running from Cambridgeshire to Gloucestershire. (2) During the 19th century, vinyards almost disappeared from the UK. In the 1800s, only 8 were reported. (3) In the 1950s, vinyards started reappearing, and they have increased in numbers rapidly over the past few decades. There are now over 400 in England, extending much further north than ever before (e.g., Yorkshire and Lancashire). English vinyards are probably not actually a good climate proxy, since they're affected by other factors like trade, the economy, consumption preferences, etc. But if one insists on using them as a proxy, they nicely agree with the consensus view: the North Atlantic experienced a mild Medieval Warm Period, a cool LIA, and a rapid warming post 1950, now to levels greater than the MWP (if you go by vinyards).
  10. Skeptical Science housekeeping: Twitter and double-posts
    Man, I send you a tweet last day thanking you for your efforts, let me thank you here again. Excellent Site
  11. Hockey sticks, 'unprecedented warming' and past climate change
    #27 batsvensson "If CO2 can make the planet come out from an ice age isn't it also a plausible idea that CO2 can prevent the planet from entering an ice age as well? " Sure. And we may already be past that point, relative to the variations of the other factors during the last 500000 years. With values in the upper tail of the current estimated probability density function for CO2 sensitivity, we probably are.
  12. Hockey sticks, 'unprecedented warming' and past climate change
    #29 Riccardo It IS about sensitivity, at least I think so! :-) My initial question was whether a 3 deg sensitivity at the 280-560 ppm doubling would imply the same sensitivity at the next doubling. This is not irrelevant for the current theme: If, for instance, sensitivity falls with increasing ln(CO2), CO2 may actually have played a bigger role in the climate variations of the reconstruction period than assumed - CO2 was, most of the time, lower than now. It is also a question of how to define 'sensititity'. Some model runs indicate that 100 year sensitivity may be only about half of equilibrium sensitivity, which may take several hundred years to reach. It's not quite implausible that the more radiative overlap, the longer the system may take to reach equilibrium. And the relevant indicator here is the observed radiation balances, not the expected. And because the H2O/CO2 ratio varies so much spatially and temporally, I think it may be hard to make good estimates of the net effects of overlapping. Making too simplistic assumptions can lead us very far astray.
  13. Hockey sticks, 'unprecedented warming' and past climate change
    SNRatio, you can't be so generic about band overlap. For example, the main contribution to CO2 absorbtion in the atmosphere is at about 600 cm-1 where there's no overlap with water vapour; other bands do overlap and there there's almost no contribution by an increase in CO2 concentration. For this reason CO2 absorption is essentially independent on H2O concentration. This was about forcing and the reason why it is more or less logarithmic. Then comes feedbacks and climate sensitivity, but it's a completeley different story.
  14. Skeptical Science housekeeping: Twitter and double-posts
    Thanks for that tip John. Is it possible to add a search box to that feature so that the lists in the drop-down boxes get filtered by a search term applied to the pages they refer to?
    Response: That's a clever idea, I've added a search form to the Link To Us page. Many thanks for the suggestion!
  15. Hockey sticks, 'unprecedented warming' and past climate change
    batsvensson @ 27: I think that it sounds pretty plausible to me. But what happens if we aren't heading into an ice age, and we throw that additional forcing on top? That seems to be the issue at present. WAG @ 23: a colleague of mine summed it up nicely. There have been climate changes in the past, many were quite large. The difference is that we weren't around to see them. 'We' being 'human civilisation' - there were hunter-gatherers around at the end of the last ice age, but the entire development of human civilisation has taken place in a relative stable period of climate history.
  16. Skeptical Science housekeeping: Twitter and double-posts
    By the way, I just noticed the 'link to this post' link that John has at the top of each of his posts. Up til now I've been typing out the links manually - doh! Use it people, It'll significantly enhance your wack-a-mole capability.
    Response: Even more useful is the "Link To Us" page (look for the link in the top navigation links) which generates up to 5 URLs for you. It also gives you the option to either generate a plain URL, HTML link or even a short answer along with the URL.
  17. Skeptical Science housekeeping: Twitter and double-posts
    That may have been me Em, I'm constantly pointing people here. John provides the most incisive, concise explanations of the science anywhere. Thanks John! Lately I've been seeing 'skeptics' trotting out their lame argument that because there were vinyards in England during the Roman period, therefore global warming isn't happening. But you don't have that on your hottest skeptic arguments. Perhaps it is just too lame to add to your list, but it would be handy to be able to point them at a concise rebuttal.
    Response: The general argument is addressed indirectly when answering the argument "The Medieval Warm Period was warmer than today". The answer is that while certain regions show past warmth comparable to recent decades, the global average temperature is cooler over the past 1,700 years (Mann 2008).
  18. Hockey sticks, 'unprecedented warming' and past climate change
    "a positive feedback system which enabled our planet to come out of a global ice age." If CO2 can make the planet come out from an ice age isn't it also a plausible idea that CO2 can prevent the planet from entering an ice age as well?
  19. Skeptical Science housekeeping: Twitter and double-posts
    I was lead to this site by somebody posting a comment on The Age website, and I am so glad I found it! I had been reading comments made by sceptics on forums like The Age, and trying to make informed comments myself, but the whole tone was so shrill and relied in the end to name calling and be-littlement of people with opposing views (the amount of times I was told to go and "educate" myself for having a view that sided with scientific results not conspiracy theories!). This site is like a drink of cold water - very refreshing!
  20. Hockey sticks, 'unprecedented warming' and past climate change
    Chris #17 I agree the Nature blog isn't peer reviewed I did suggest it as a jumping off point because it does give a view of the development of the hockey stick idea as well as linking to some peer reviewed papers that questioned the science. I can accept that Mann didn't stumble on the MWP as a regional phenomenon in 2009 but I'd question the validity of the papers you present Crowley 2000 - The main conclusion of this paper is that the MWP can't be described as warmer than 20th century. It describes MWP as occuring in the NH only because it recognises insufficient data in the SH. You can't say something is regional just because you don't have data for the other regions. Bradley 2003 - Again this paper bemoans the lack of records in the tropics and SH. Concludes that evidence of a MWP is safest in Europe. Again MWP as a regional phenomenon can't be deduced due to the poor spread of data. Jones 2004 - "Regional conclusions, particularly for the Southern Hemisphere and parts of the tropics where high-resolution proxy data are sparse, are more circumspect." Osborn 2006 - This states it is an analysis of the NH. It is impossible to draw conclusion on SH. They are generally working with averaged data from 14 proxys and make no attempt to define spatial variation. Based on averaged data they find evidence of a MWP. Wanner 2007 - I don't fully follow this 38 page blockbuster again I'll stick to one quote to prove my point. "It is still an open question whether the MWP–LIA transition was caused by external forcing, and its spatial extent is still not entirely clear" It appears the MWP is a northern Hemisphere phenomenon only because we have data for the NH. It is funny that with essentially the same data sets Mann in 2009 can draw such definitive maps of the globes temperature 1200 years ago. It should be remembered he is still working with only a handful of proxy data sets in the tropics and whole of the southern hemisphere. I assume he uses modelling to fill in the huge gaps. Mann's desire for certainty in his work is his shortcoming.
  21. Skeptical Science housekeeping: Twitter and double-posts
    I just wanted to say thanks also for this great site, its a invaluable tool, filled with science, logic, reasoning and critical thinking. Keep up the great work.
  22. Skeptical Science housekeeping: Twitter and double-posts
    You're right NewYorkJ. I only started coming to this site a little over a month ago. I was appalled at the media's grab at the "controversial" science around global warming and couldn't believe how quickly people lapped it up. So even if it is a sad result it has forced me to do proper research on global warming so I can actually fight back with facts and openness. (and yes part of the spike in web traffic is to do with me, my family and friends I have forwarded the link to which has to be a good thing!) Thanks John!
  23. Skeptical Science housekeeping: Twitter and double-posts
    On a general topic, web traffic to your site (according to alexa.com) has increased significantly over the last couple of months. This is true of most blogs on climate science (or those pretending to cover climate science) and is likely a sad result of the stolen emails incident. A big chunk of the population doesn't care about science unless there's some juicy gossip being perpetuated by an eager media machine. The traffic increase here appears to be a bit sharper relative to previous traffic than with other sites. I think the expansion to a blog format is a good thing. This site helps inform visitors what the science says, allowing them to cut through the spin they might be reading elsewhere. Keep up the good work. Not a big deal or at all high priority, but you might want to update the following skeptical argument at some point (see my last post in the comments section): http://www.skepticalscience.com/1934-hottest-year-on-record.htm
  24. Hockey sticks, 'unprecedented warming' and past climate change
    Mizimi @21 H2O and CO2 have the same number of IR active vibrations - 3. An absorption band at a given frequency is due to a specific vibration. For example the 650cm-1 CO2 absorption is due to the (doubly degenerate) bending mode. So more asymmetry in a molecule does not mean more absorption at a given wavelength. It usually means more wavelengths at which it absorbs. However asymmetry will complicate the rotational-fine structure of a particular IR absorption, however H2O's rotational fine structure will be quite dispersed because of its light mass (18 compared to CO2's 44)
  25. Climate's changed before
    I'm curious. Do we know what caused the reversal in past warm periods in the Earth's history? What made it get cool again? Clearly, despite CO2 having a positive feedback loop, we didn't get runaway warming. We're not living on Venus. Even if we're headed for higher temps, rising sea levels, drought, mass extinctions, catastrophic loss of human life, etc. At some point won't it top out an head back to another ice age? What's prevented a runaway greenhouse effect in the past?
  26. Hockey sticks, 'unprecedented warming' and past climate change
    re #21 It depends on a lot of things. Obviously it depends on the wavelength - you are really only talking about wavelengths where the CO2 and water vapour absorption bands overlap. In such a case the relative absorption is chracterised by the (wavelength-specific) absorption coefficient. Water vapour does have a stronger absorption than CO2 over the range of longwave IR wavelengths/frequencies relevant to the greenhouse effect (the wavelengths/frequencies appropriate for surface heat dissipation to space). All of that is "accounted for" in analysis of the greenhouse effect and the effect of raising greenhouse gas levels.
  27. What do the hacked CRU emails tell us?
    I find it incredible that you would suggest that all the more than 31,000 scientists who signed the document refuting the concept of AGW, including 9,000 PhD's, and including geophysicists, oceanographers, meteorologists, astrophysicists, atmospheric scientists and climatologists, do not have the academic credentials to validate their views! Moreover, those signatories are all from the U.S.; assuredly there are many thousands more scientists internationally who agree as well. Re the recently exposed emails, when scientists work to stymie the efforts of their peers to obtain information, as has been revealed, it's the antithesis of scientific community and process. All scientists should be insisting on a thorough and transparent investigation.
  28. Skeptical Science housekeeping: Twitter and double-posts
    I second the comments above. This is an excellent site. Informative and classy with a straightforward presentation of the science. What more could any citizen want...
  29. Hockey sticks, 'unprecedented warming' and past climate change
    John - I think there's another implication to the way skeptics use the "climate's changed in the past" argument. It's not just that "climate changes naturally, so humans aren't causing it" - it's also like, "climate's changed much more in the past, so it's nothing to worry about. Life goes on." My usual response is that, "yes, we've had ice ages and warm periods in the past, but what's important is the rate of change going on now," but I was hoping you could elaborate more on the implications of past climate change. e.g., just because climate's changed in the past doesn't mean it's nothing to worry about.
  30. Hockey sticks, 'unprecedented warming' and past climate change
    PS: or is it just a question of which molecule gets 'hit' first?
  31. Hockey sticks, 'unprecedented warming' and past climate change
    Question....based on SNRatios post 20.....I would expect a differential in IR absorption between WV & CO2, based on concentration, sure, but also on assymetry - WV molecule having more ways that the bonds can be stressed. So the question is, in a given sample of air where the number of CO2 molecules is equal to the number of WV molecules, and there is insufficient IR to affect all the molecules -is there preferential absorption by WV? Apologies if the question is badly worded.
  32. Skeptical Science housekeeping: Twitter and double-posts
    I'll add my thanks and appreciation for the efforts at this site. The Signal to Noise ratio is high in the comments also. Cheers
  33. Hockey sticks, 'unprecedented warming' and past climate change
    Riccardo - Surely a linear function of ln(x) is a linear function of ln(x) for as long as you want - and then some. But - to mention just one thing: There is considerable overlap between IR absorption spectra of CO2 and H2O. Which may imply that changes in CO2 absorption with concentration is not independent of H2O, and the very idea of feedback f>0 is that other things, H2O vapor not the least, change with CO2. The whole thing could just add up to sensitivity increasing with CO2 (within bounds, of course), or it could decrease. Forcing-wise, we seem to be in a unprecedented situation now, so we can't just compare and apply.
  34. Skeptical Science housekeeping: Twitter and double-posts
    John, thank you again and again for your tireless efforts on this site. Over the past few months the blog has really been outstanding. There is no better site on the internet for the informed and intellectually curious lay reader to learn about and discuss the science of climate change.
  35. Hockey sticks, 'unprecedented warming' and past climate change
    They're not absolute temperatures RSVP. Obviously the top of the Antarctic ice sheet at Vostock isn't at a temperature anywhere near positive values! I think the temperatures are actually temperature differences between then and current temperatures, and the temperature difference may correspond to the air temperature in the atmosphere where the precipitation forms, since the temperatures are based on isotopic fractionation. It would be helpful if this was more carefully specified in graphs, although it obviously is in the scientific papers from which the graphs are derived. The warmer last interglacial is associated with much greater ice melt than now; the evidence indicates that sea levels were 4-6 metres higher then, than now...I believe there is some uncertainty about exactly how warm the previous interglacials actually were.
  36. It's the sun
    These words spring to mind. “No amount of experimentation can ever prove me right; a single experiment can prove me wrong.” and "If we knew what it was we were doing, it would not be called research, would it?". -- Albert Einstein (1879-1955) [German physicist] Just because its warming does not PROVE its CO2. Cause and effect issues. The commentary on radiative "forcing' is also a bit hard for me to understand. Is it another word for Convection? After all, hot gases rise (when not trapped in a glass greenhouse) and when surrounded by cooler gases, they lose that latent heat, clods are created, humidity changes. Where are the records and observations of the changes in humidity and cloud cover?.
    Response: "Just because its warming does not PROVE its CO2. Cause and effect issues."

    That is true. The reason we know the warming is caused by CO2 is because satellites and surface measurements are observing more infrared radiation being trapped at the specific wavelengths that CO2 absorbs energy. That is what is meant by 'radiative forcing' which is just another term for an imposed energy imbalance. More CO2 is causing less radiation to escape back out to space which causes an energy imbalance. The result is the planet is accumulating heat.
  37. Hockey sticks, 'unprecedented warming' and past climate change
    On the graph of Vostok Ice Core data above, the temperature peaks around +3, +2, and +4 degrees. How could any ice have survived these peaks?
  38. Hockey sticks, 'unprecedented warming' and past climate change
    re #15 No one is that concerned about "regurgitating hockey stick arguments" HR. It's unfortunate that this isn't always done honestly and with a bit of scientific rigour (although one shouldn't have great expectations about the more dismal corners of the blogosphere!). After all the large amount of aditional paleoproxy data since the original "hockey stick" has pretty consistently supported the initial conclusions of that study concerning the anomalous nature of late 20th century warming. Alley's analysis of GISP 2 temperature proxy data for the Greenland ice sheet is also consistent with the "hockey stick" as originally presented. It's unfortunate that some blogger has made a false representation of the warming at the Greenland ice sheet surface during the last 100 years (see my post #7 above), but again, there does seem to be a concerted effort to misrepresent the science on climate-related matters. Your comments about "criticism of the science...moved....into peer reviewed literature" isn't really correct (of course all science has an essential critical element); a Nature blog simply isn't "peer reviewed science" HR! You're also incorrect in your assertion that "Mann has refined his arguement this year to suggest that MWP was a regional phenomenon". Mann has presented evidence for a regionality of the MWP for many years (as have many other scientists). That's simply what the evidence indicates, and there are many studies in the peer reviewed literature that indictaes that the MWP was represented predominantly in the high Northern latitudes and was spatially and temporally non-homogeneous elsewhere. See, for example, the following papers [*] that discuss evidence for the regionality of the MWP in comparison with the global scale nature of late-20th century and contemporary warming. This is a conclusion that has been around for quite a while....it's certainly not a "new version". You're right that "this particular bit of science has been seriously affected by its collision with politics". How true. But why not focus on the science and treat the political nonsense on the blogosphere with the disdain it deserves? [*] PD Jones and ME Mann (2004) Climate over past millennia Reviews of geophysics 42, RG2002 T. J. Crowley and T.S. Lowery (2000) How Warm Was the Medieval Warm Period? AMBIO: A Journal of the Human Environment 29(1):51-54 Bradley, R.S., Hughes, M.K., Diaz, H.F. (2003) Climate in medieval time Science 302, 404–405 Osborn TJ, Briffa KR (2006) The spatial extent of 20th-century warmth in the context of the past 1200 years Science 311, 841-844 H. Wanner et al. (2007) Mid- to Late Holocene climate change: an overview Quaternary Science Reviews 27 (2008) 1791–1828 etc. etc.
  39. Hockey sticks, 'unprecedented warming' and past climate change
    SNRatio, the 3 degrees per doubling concentration holds as long as the simple logarithmic approximation holds. For exaple, the IPCC TAR quote three different aproximations for the forcing. You get 3.71 W/m2, 3.98 W/m2 and 3.97 W/m2 respectively for doubling from 280 to 560 ppm. If you double from 140 to 280 you get the same 3.71 W/m2 (obviously), 3.8 W/m2 and 3.45 W/m2 respectively.
  40. Hockey sticks, 'unprecedented warming' and past climate change
    You can point at skeptics regurgitating the MWP/Hockey stick arguement over and over again but it shouldn't be forgotten that it was warmers who really shot this to fame. Al Gore and the IPCC 2001 made sure this would be at the centre of the climate change debate. Critisism of this science has moved from marginal skeptic websites into peer reviewed literature. You could look at the Nature blog as a jumpimg off point. For this reason I think it's wrong for John to dismiss all this as "the inevitable consquence when forced to respond to rehashed skeptic arguments." As John mentioned, in a previous post, Mann has refined his arguement this year to suggest that MWP was a regional phenomenon. It will be interesting to see if this new version can stand up to inspection. You could view all this as the normal process of a developing science but we shouldn't forget this particular bit of science has been seriously affected by it's collision with politics.
    Response: The regurgitation was refering to the use of the Climate's Changed Before argument. The YouTube movie doesn't look to dispel the hockey stick - but demonstrate that over longer periods, there have been even greater changes in climate. I've yet to encounter any peer reviewed science claiming that past climate change means that climate is not sensitive to the radiative forcing currently being imposed by rising carbon dioxide.
  41. Hockey sticks, 'unprecedented warming' and past climate change
    It would be nice to have a collection of properly calibrated temperature series from cores in one easily accessible post. As chris points out, the 'instrumental record' part of fig 1 is probably misleading. Maybe not the most rewarding task, but I fear WUWT and likes will bring up this again. And again and again and again. I think it would also be worthwhile to go more into the orbit/precession/nutation material, to give better understanding of the forces at work - AND - the sensitivity.. Apropos sensitivity: Who is quite sure that a 3 deg sensitivity at the doubling from 140 to 280 ppm necessarily implies a 3 deg sensitivity at the next doubling, to 560 ppm? I'm not :-)
  42. Hockey sticks, 'unprecedented warming' and past climate change
    re #12 (i) No one claims that 15-18 ppm rise will produce a 1oC rise in temperature, livas. Taking the central value of the likely range of climate sensitivities of 3 oC (the temperature rise from doubling atmospheric CO2) the equilibrium temperature rise is expected to be: Temp rise = ln([CO2]2/[CO2]1)*3/ln2 where [CO2]1 is the starting [CO2] level, [CO2]2 is the end [CO2] level, 3 is the climate sensitivity and ln2 refers to the doubling. (ii) Note that water vapour doesn't remain at the same level. The water vapour concentration in the atmosphere rises as the atmospheric temperature rises. So water vapor provides a positive feedback to whatever forcing increases the atmospheric temperature.
  43. CO2 is not the only driver of climate
    cleanwater, you forgot to mention Ångström! It's a pitty. Apart from your random quotes and some standard shouting, you're welcome to discuss science, if you'll ever will. P.S. much too easy to copy and paste to leave garbage around ;)
  44. Hockey sticks, 'unprecedented warming' and past climate change
    Chris, you have put it very well. For every 1oC rise in temperature we observe as a result an additional 15-18ppm of CO2 levels. Of course, this does not mean the opposite direction. 15-18ppm rise of CO2 levels do not necessary means that it will produce a 1oC rise in temperature, which is about what the anthropogenic global warming supporters claim. Not, if you ignore the fact that the other 95% of global warming factor which is water vapor will likely remain at the same levels. Not, if scientists, as I hear, have not concluded to the basic physics behind the relation of water vapor, cloud formation from water vapor and the effect of clouds in global warming.
    Response: "15-18ppm rise of CO2 levels do not necessary means that it will produce a 1oC rise in temperature, which is about what the anthropogenic global warming supporters claim"

    What the peer reviewed science finds is that a doubling of CO2 leads to 3°C warming. Eg - if we move from the pre-industrial levels of around 280 parts per million (ppm) of atmospheric CO2 to 560 ppm, the CO2 forcing would cause 3°C warming. We're currently at around 385ppm.

    For more on water vapor and how it enhances CO2 warming, see water vapor is the most powerful greenhouse gas.
  45. Hockey sticks, 'unprecedented warming' and past climate change
    Livas, analysis of the Milankovitch cycles that underlie the transitions from glacial to interglacial periods and back again, indicates that the present interglacial will likely be very long lived in the context of the last several cycles (e.g. around another 50,000 years of interglacial to go before the next descent into a glacial maximum) e.g. A. Berger and M. F. Loutre (2002) An Exceptionally Long Interglacial Ahead? Science 297, 1287-1288 http://www.sciencemag.org/cgi/content/short/297/5585/1287 On the lead/lag phenomenon of CO2/temperature. There's no question that temperature changes during ice age cycles lead CO2 changes by a few hundred years (at least in the Antarctic cores; the CO2 changes lead temperature changes in Greenland ice cores). The CO2 rises (during insolation-driven glacial to interglacial transitions) amplify the primary warming resulting from insolation-driven ice melt/albedo contributions and water vapour feedbacks. One can get a handle on the amount of atmospheric CO2 that results from glacial-interglacial transitions. The atmospheric CO2 levels rise pretty faithfully during the slow, 5000-year, glacial-interglacial transitions from around 190ish ppm to 280ish ppm (and back to 190ish ppm in the following descent to glacial conditions: http://en.wikipedia.org/wiki/Ice_age This is in response to a global temperature change near 5-6 oC. So each oC of warming produces around 15-18 ppm of raised CO2 levels (90 ppm rise resulting from 5-6 oC rise). Obviously the massive rise in CO2 from preindustrial levels (280ish ppm) to now (386 ppm and rising) can't have resulted from a temperature rise, since we've only had around 1 oC of this since pre-industrial times.
  46. Hockey sticks, 'unprecedented warming' and past climate change
    What should also be mentioned is that the graphs compare the global temperature record with a local record. I think that region in Greenland is more sensitive to changes and has warmed more than the global average, so the comparison is not valid.
  47. Understanding Trenberth's travesty
    Philippe, I agree...in my opinion the CERN experiment will never be conclusive about any putative effect of CRF variation on clouds, let alone climate. It's simply not an experiment that can yield information on this subject. The experiment will no doubt yield useful physicochemical information on aerosol particle nucleation by gamma rays under controlled conditions in a particle chamber, and its response to variation in the composition of atmospheric mimetics. Also, in my opinion, the main proponent of the CERN experiment has misrepresented the science on contributions to historical temperature variation, as a way of "beefing up" the justification for the experiment [*]. ([*] see posts #99, #127 here: http://www.skepticalscience.com/Climate-time-lag.html )
  48. Understanding Trenberth's travesty
    oops. In my post just above, I meant to say in paragraph "3.": The temperature variation leads the CRF variation reconstructed from cosmogenic isotope (14C) formation, through the MWP period. (In other words the CRF variation can't be causally related to the temperature variation of the MWP).
  49. Hockey sticks, 'unprecedented warming' and past climate change
    Looking at Figure 2 makes me wonder if any scientist has been able to make a computer model to reproduce this “near” periodical cycling between -8 and current temperatures in the past thousand years scale. Those supporting anthropogenic global warming say that solar activity is stable over the years, so these major temperature changes can depend mostly on earth’s axial tilt than any other factor. If a computer model is able to reproduce and verify all these past temperatures, then it would have chances to predict future climate as well. On the other hand, the skeptical argument says that coming out of the ice age into interglacial there is a delay of hundreds of years after which CO2 rises. They argue that CO2 is a product of temperature rise (maybe with some feedback effect) and not the primary cause of the temperature rise. Is it only me feeling I should enjoy the last years of interglacial before going into the next ice age?
    Response: We address the CO2 lags temperature argument here. Basically, warming causes CO2 outgassing from oceans. However, this doesn't mean CO2 doesn't cause warming - this is proven by a laboratory measurements plus empirical observations of an enhanced greenhouse effect. When you combine the two effects - warming causes CO2 rise and CO2 rise causes warming - you get a positive feedback system which enabled our planet to come out of a global ice age.
  50. Philippe Chantreau at 03:32 AM on 16 December 2009
    Understanding Trenberth's travesty
    The CERN experiment on cosmic rays is anything but conclusive so far. They are struggling to prevent interactions with the chamber wall from completely ruining the experiment. In my opinion, it does not bode well for the hypothesis in the real world, where CCN are found in the millions per liter of air, whether over land or water. And over the ocean these CCN include lots of ions.

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