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Good climate debate FAQ

Filed under: — group @ 13 March 2006

There are a number of topics in climate science that are frequently misunderstood or mis-characterised (often by those trying to ‘scientize’ their political opinions) that come up again and again in climate-related discussions. RealClimate tries to provide context on many of these issues, and commentaries on the 1970s ‘global cooling myth‘ or whether water vapour is a feedback or a forcing are among our most referenced pieces (see our FAQ category). However, our explanations of specific points have often appeared in the middle of a larger piece, or in the comment section and are not clearly referencable. Since many of these same points keep coming up in comments and discussions, having a clear and precise resource for these explanations would be very useful and we have thought about doing just that. But it now appears that we have been beaten to the punch by a new blog run by Coby Beck, a frequent commenter here and at sci.env. His new blog ‘A few things ill-considered‘ has a point-by-point rebuttal of almost all the most common ‘contrarian’ talking points. The list of topics by category is a good place to start, and it shows the huge amount of work done so far. We’re very impressed!


87 Responses to “Good climate debate FAQ”

  1. 1
    Coby says:

    Wow, thanks for that! The best news is that now that you all have endorsed it I can be reassured that you will correct any of the scientific errors I will undoubtably make ;)

    Topic suggestions and missing substantiations welcomed.

    [Response: No problem. I think William suggested that it be placed in a wiki format so that it can be updated and corrected efficiently - that might be worth thinking about. We'd love to help out. Similarly, let us know if you want something dealt with in a little more depth... - gavin]

  2. 2
    Dan Bailey says:

    I’ve had friends and family bring up quite a few of those arguments in the past, so from now on I can just refer them to Coby’s site :D

  3. 3
    Stephen Berg says:

    Coby, your site is great! Keep it up!

  4. 4
    cp says:

    I’ve been reading this for some time now. The point by point explanations was a nice thought, just make sure -all of you scientists :) – that it stays as scientifically accurate and up to date as possible.

  5. 5
    Richard Ordway says:

    Already, I see many comments on your website :)

    Thanks for this service to humanity.

  6. 6
    Ed Arnold-Berkovits says:

    This is a wonderful resource. What would be great is a What Will They Think Of Next?” section there, or described here. That way they can be “headed them off at the pass”. I’m particulary thinking of the
    1. Trend skeptics (it’s no happening)
    2. Attribution skeptics (it’s not our fault)
    3. Impact skeptics (it won’t be that bad)
    line of thought from Stefan Rahmstorf’s article for Munich Re (http://www.pik-potsdam.de/~stefan/Publications/Other/rahmstorf_climate_sceptics_2004.pdf) where explains how most skeptics are finally convinced it’s happening, and are somewhat through the fact that man has caused (and is causing) GW. Now I feel like I’m seeing more of “it won’t be that bad” (especially in those pesky ‘balanced’ news reports) – and while modelling gives some regional impacts, obviously the generalizations will have to do until the science catches up.

    Here’s some general areas about Why They Think It Won’t Be That Bad But It Will:
    - First and foremost is that the predictions are just that – predictions. Could the GW be below the prediction? Yes, and it could easier be *higher*.

    - Northwest passage opened up north of N. America with the melting Arctic ice
    habitat destruction, native peoples uprooted are obvious, but I’m thinking of more “business” impacts such as melting permafrost cracks pipelines and transportation roads. Maybe insurance costs going up on ocean transports due to more/more intense storms?

    - Carbon fertilization effect
    only good for a small increase (I think?) and along with higher temps is bad

    I’m sure there’s a whole host more…..

  7. 7
    pete best says:

    A great achievement

  8. 8

    Rebuttals
    “sierra club compass”: Rebuttals .

  9. 9
    grundt says:

    Excellent work. Bravo, RealClimate group and Coby’s “A Few Things Ill Considered” (and also many other people who contribute with very important comments).
    Muchas Gracias!

  10. 10
    Steve Bloom says:

    Nice work, Coby! Also, re #8, everyone note that the new Sierra Club blog is heavily featuring material from RC (and now from A few Things Ill-Considered). The Club blog is a good mechanism for getting this material out to folks all over the US and Canada who really need it as a tool in implementing the Club’s new #1 priority on climate change.

  11. 11
    Stephen Berg says:

    Here’s the home page for Tim Flannery’s superbly-reviewed book “The Weather Makers”:

    http://www.theweathermakers.ca/

  12. 12

    The Lovelock thread from February is closed. May I comment here?
    Lovelock’s new book has a page of maps showing:
    Hotter = mostly desert over the world
    Colder = mostly forests.
    My readings of paleoclimatology usually reverse this…
    (eg: “Why does Gaia prefer ice ages, with their larger deserts and reduced tropical rainforests”. Blair Dowden â�� 19 Feb 2006)
    I usually read that colder periods have a lot of dust, implying deserts.
    Hotter periods are usually described as forested (eg dinosaurs at the pole)
    Caveat: tropical forests seem currently vulnerable to ringbarking & then burning, and some say once gone they may not return (perhaps meaning ‘will take many hundreds of years’?) …Walk about in Tikal in thick jungle, in what was a city centre 1100 years ago. The ‘wild’ forest is reportedly rich in fruit trees, escapees from classic gardens?

  13. 13
    Todd Albert says:

    Great site!

    As far as types of climate skeptics, what about those that claim that we’ve passed the tipping point, and there is nothing we can do to stop the changes from happening now?

    [Response: Well, at a discussion we had over lunch last week, a cynic pointed out the three phases of skeptics' response to environmental problems:
    Phase 1: "There is no problem."
    Phase 2: "OK there is a problem, but it's exaggerated and not really serious."
    Phase 3: "Now it's too late to stop it."
    I notice that recently climate skeptics arguments are indeed shifting into phase 3; more and more you hear the argument that yes, there is a serious problem, but it's better to adapt to the changes rather than try and stop the warming.
    Any argument will do, as long as we don't have to change... -stefan]

  14. 14
    Dragons flight says:

    Coby, RealClimate, and others on both sides of the divide seem to be slowly (or not-so-slowly) spreading my work with Wikipedia around the net. Not to mention the appearances at AGU and the recent NAS panel. So, I am wondering: Does anyone have any requests?

    [Response:You could add the curve of recent (since 1952) modern measurements of solar activity, such as cosmic galactic rays and 10.7 cm solar flux: there is no clear trend in these records (e.g see Richardson, I. G., E. W. Cliver, and H. V. Cane (2002), 'Long-term trends in interplanetary magnetic field strength and solar wind structure during the twentieth century', J. Geophys. Res., 107(A10), 1304, doi:10.1029/
    2001JA000507 or Benestad, GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L15714, doi:10.1029/2005GL023621, 2005). -rasmus]

  15. 15
    Eachran says:

    I agree Mr Beck’s site is really excellent.

    I am relatively new to understanding global warming and only became more interested through reading wikipedia and subsequently asking William to point me in the right direction for reading – I liked his style and trusted what he wrote. He did, and in that way became a “father figure” for me – dont all laugh at once particularly when he is roughly the same age as my own children and with his own children younger than some of my grandchildren.

    Through that I came to RealClimate and came to trust them too and some but not all, regular posters : I am not so sensitive as some of you who think that “mockery” (see the Greenland Ice blog) is not part of a scientist’s tools : we are all human and trust isnt broken by mockery – it must be difficult for people like William and Gavin, both on record as saying they are always right or maybe almost always right, to deal with the same tired old arguments every day. But they do it in good spirit and that takes guts.

    So the issue for me is “trust”. Now RealClimate is accrediting (if I may use that word) Mr Beck’s site on the basis that it is good and accurate and on the assumption, certainly assumed by Mr Beck, that corrections for errors will be dealt with or at least posted by RealClimate. Is that correct please? Editorial control?

    Please dont think I am being overly critical here but I’ve been there and done that – it has something to do with age.

    Understanding and dealing with virtual communities is also something to do with age – I havent been there and done that : at least not yet but I’m learning fast.

    Good luck to all and keep up the good work.

  16. 16
    Peter Hearnden says:

    Re #14. Rather OT, but when you see ‘they are licensed under the GNU Free Documentation License.’ you think, (or at least I did…), ‘oh, so you need a licence to use them? Pity.’.

    I then went on to read the licence and instead of saying ‘these documents can be freely copied and used’ there is a vast webpage of words saying, well, that..I think?

  17. 17
    Tom Rees says:

    Shameless plug for my site, while we’re on the subject of FAQs: http://www.brighton73.freeserve.co.uk/gw/globalwarmingfaq.htm Bits of it are getting a bit long in the tooth now tho :D

    Dragonsflight, I use your figures – they’re excellent. Do you have one showing the latest on sea level rise (e.g. Church’s 2005 paper that finds an acceleration).

  18. 18
    Florifulgurator says:

    I can’t hear the word “sceptic” anymore. Wasn’t that word populismarized by Lomborg & friends? Why not use a word made by our own, like denialist ?

  19. 19
    Hank Roberts says:

    Drag, some of your figures go left to right, others go right to left (time sequence). I realize the originals you draw from do that. But if you could always put the old on the left and the new on the right, or vice versa, and do it consistently, it’d make the images much easier to comprehend when viewed as a group.

  20. 20
    Blaine Johnston says:

    Dragonsflight: It seems like every time I hear someone with little knowledge of the field talk about your figures they ask, “But why isn’t there huge warming at the end? The only data set which shows big warming near the present time is the modern instrumental record. That must be the one that’s wrong.”

    The reason, of course, is that most of these data sets end before the modern rapid warming and hence miss most of it, but also end close enough to the end of the graph that this is not obvious that they do not continue to the present. It would be nice if this was made more clear on the graphs.

  21. 21
    Leonard Evens says:

    Great job Coby!

    But some of the entries need proof reading. In a brief look of some of the topics, I found one spelling error and one case of a plural noun and singular verb. I thought of posting comments, but it would seem easier to do it all at once. Let me know if you would like some help with the proof reading.

  22. 22
    Pete Best says:

    I am reading the Tim Flannerys the Weather Makers at the moment myself and it is a fascinating read for the most part. I wonder if anyone at realclimate has picked it up and taken a look. Be good to hear a few comments from Gavin etc on the book.

    According to Tim Flannery, climatologists seem to be suggesting that by 2050 at present rates of fossill fuel consumption we will have hit 550 parts per million of CO2, double pre industrial levels and this would indeed spell disaster as global warming would be around 5 deg C on average give or take a degree or two.

    There are many other fascinating things in the book especially to do with the complexity of climate, especially feedback and the non linear nature of all things bound to earth.

  23. 23

    Re #21; the conventional wisdom is that the warming due to CO2 doubling is around 3 C or 5 F, not 5 C. The sensitivity you quote is considered barely plausible by some and implausible by others; it’s certainly far from a consensus estimate.

    Also (and this is a crucial fact in understanding the situation) the warming is not instantaneous. About half the warming due to a CO2 perturbation is delayed by some decades, so the likelihood of seeing 5 C by 2050 is very small. On the other hand, while we won’t see the warming due to a given CO2 perturbation instantaneously, it’s pretty much certain that we will see it eventually.

    Fortunately there is almost certainly still enough time to avoid anything like a 5C perturbation, which would be vastly more catastrophic than the loss of a percentage point or two in economic growth rates that has some people so exercised.

  24. 24
    Pete Best says:

    I did not say 5c by 2050, I said a doubling of CO2 by 2050, and yes climate latency is many decades behind so 5C (give or take a degree or two) by 2100 I think is what he is saying.

    He also mentions Global Dimming and it possibly offsetting global warming but I am unsure about this as realclimate has reported it as bogus in a recent article, well it needs more investigation anyway.

    [Response: Doubling of CO2 by 2050 is pretty pessimistic - 2080 or so is more likely (in the unlikely outcome that nothing is done to reduce emissions). PS. We never said that Global Dimming was 'bogus', just that a particular documentary on the topic was rather alarmist and did not give enough proper context. - gavin]

  25. 25
    llewelly says:

    Re Dragons Flight:
    Overall, I think your work is excellent. However, some nitpicks:

    Your 25 year graph uses the CRU dataset, which has 2005 as 0.1 C cooler than 1998. The NASA GISSTEMP dataset has slightly different values, with 2005 being a bit warmer than 1998. Due to NASA’s results, here in the US 2005 was widely reported as ‘the warmest year ever’. I feel some may look at your graph and think ‘Aha! 2005 was actually *cooler* than 1998! the liberal media is wrong, and global warming is a hoax!’. I’m not suggesting you switch to GISSTEMP (since my understanding is the two agree within their uncertainties), but A short explanation of why your graph appears to differ with certain media headlines, and the meaning of this difference with respect to the recent warming trend would improve your page. Relevant RealClimate article .

    Links to other temperature data sets would also be nice.

    Like Hank, I think it’s confusing for the layman that nearly half (450 kyr, 5 Myr, 65 Myr, and 500 Myr) of the graphs are ‘backward’. I know this is a result of a long and reasonable tradition from geology, paleontology, and paleoclimatology, of graphing deep time as increasing to the right, but non-scientists are used to seeing the present on the right, not on the left.

    I notice your 12 kyr graph has a mark indicating the 2004 temp, and an explanation that the recent warming is below the effective resolution of the graph (with respect to rapid fluctuations) . This is much appreciated, and I think something similar would improve the 450 kyr, 5 Myr, 65 Myr, and 500 Myr graphs.

    Finally, thank you for your work on graphs, and thanks to Coby for his ‘a few things ill-considered’ (finally, one on-topic phrase … :-) ), and thanks to RealClimate.

  26. 26
    Harry Pollard says:

    As I said to Ray, one of the worst parts of Real Climate is its excellent hyperlink system.

    One can travel around from page to page encountering masses of fascinating information. A quick look can rapidly become a marathon read (when other tasks need doing).

    Along the way through the “Climate Debate” I came across a denigration of the Medieval Warming Period, suggesting it was purely a northern hemisphere event.

    Here’s the CO2 Science Url for their discussion of this – as a global event.

    http://www.co2science.org/scripts/CO2ScienceB2C/data/mwp/mwpp.jsp

    Any comments?

    [Response: We've been trying to improve the navigation - but clearly we are not there yet! With respect to the MWP, it is not a 'denigration' to be a regional phenomena (I wonder what ENSO would think about that...). The problem with the global MWP idea is that for well dated proxies, the putative MWP doesn't tend to line up very well across regions (Bradley, Science, 2002; Osbourn and Briffa, 2005; D'Arrigo et al, 2005) and so in the global mean things tend to cancel out. But the number of quality records are not high, and so coverage is spotty. It's possible that with better data, the MWP will look more consistent, but as it stands, the evidence does not support as widespread a warming event as we have seen in the late 20th Century. - gavin]

  27. 27
    Steve Bloom says:

    Re #13 comments: I would suggest a 2a: “Well, sure we’re seeing the early signs and we can’t let the situation go on indefinitely, but it’s too expensive to deal with it now and we can be confident that advances in technology will make it cheap and easy to deal with in the future.” I’ve even seen this reasoning extended to support for building large numbers of new coal plants since the cheap and plentiful electricity will get us to those promised techno fixes that much sooner.

    Re #18, I’m beginning to lean toward evasionist. It seems that as long these folks are convinced that nothing very bad is likely to happen to them (within their lifetimes), they just don’t see climate change as a problem and will continue to rationalize inaction. Probably the classic example of this kind of thinking is Lomborg’s “Copenhagen Consensus” wherein it was argued that the money to reduce global warming is better spent on other human needs (water supply, anti-malaria, etc.). I was holding my breath for a while waiting for news of Lomborg actually working on one or more of these other issues, but now I find I’ve had to resume steady breathing.

  28. 28
    Dragons flight says:

    Re: 16, 19, 25

    I have been quietly preparing a non-Wiki site as a venue of first publication for my graphical work. In the process I have been doing things to clarify the reuse policy (which I want to be liberal) and make the series visually more consistent. As much as it galls me to do (earth science training and what not), this includes producing figures with the present day consistantly shown on the right for better comparison across the series.

    Re: 20, 25

    Putting present day marks on the very long-term plots is problematic because the scales and timing would make it very difficult to see. It also becomes a dangerously apples to oranges comparison if one tries to compare a global annual value to data that is both greatly smoothed and often less than global. As llewelly suggests I may add comments to the description pages about this.

  29. 29
    pete best says:

    Tim Flannery to me at any rate is a connectionist in the gaia tradition of earth science.

    He states on page 197/198 of his recent book that the Amazon creates its own rainfall via transpiration and increased Co2 is causing the stomata to open for less time allowing less water to escape as transpiration. Transpiration is rainfall in the amazon such is the volume of water given off. By 2100 transpiration will be 20 % less than it is now, another major factor here is a persistant el nino effect that sequesters carbon by turning land mass carbon sinks into carbon sources.Rainfall over all of the Amazon will fall from 5mm to 2mm a day. By 2100 the Amazon will begin to die basically due to global temperatures being 5 C hotter than today. Some massive release of carbon from Amazon soil will push Co2 levels to 1000 ppm.

    Stuff like that.

  30. 30
    Dragons flight says:

    Re: 17,

    As far as I know, there is no evidence of recent acceleration that is statistically distinguishable from noise. If you are refering to the Church and White paper in GRL, they are looking at data from 1870-2000, and the significance of their result is mostly constrained by what I might call a kink around the 1930s. While their data is consistent with a long-term acceleration, it is not really a compelling exposition of what might happen in the future given global warming driven climate change. Or put another way, I find their graphs less interesting than the amount of press surrounding them would suggest.

  31. 31
    mark says:

    Wasn’t the impact of Krakatoa a drop in world wide temp, by about a degree, centigrade?

    [Response: No, it was a few tenths of a degree C at most. See the CRU global mean temperature series. The global mean response to explosive volcanism and solar irradiance explains a modest fraction of the observed global mean surface temperature changes recorded since the mid 19th century, but only anthropogenic factors can explain the substantial warming trend of the late 20th century. - mike]

    The crop devastation was far more significant. The rise in global temp can be drastically offset by a volcano, in a period a lot shorter than the ‘global warming theory’.

    [Response: The statement reflects a misunderstanding of the timescales on which these different forcings primarily act. See the links provided above. - mike]

    Curious as to the output of the volcanoes, in regard to the actual co2 output v. man-made.

    [Response: Then I suggest you go to Coby's FAQ, which covers that... -Stefan]

  32. 32
    Ben Coombes says:

    RE: 24 and the response,

    With reference to your prediction that a doubling of CO2 by 2050 is pretty pessimistic, I was wondering if anybody has any data (or more likely an inclination) on the impact of fast-industrialising nations Vs the actual curbing of emmissions developed countries may achieve?
    I don’t want to be pessimistic but when I read that “China has plans for about 560 new coal-fired plants, and India 213 – without any consideration for carbon capture” (New Scientist, 2005), I do indeed become pessimistic.
    On the original thread, thanks a million to the Real Climate crew and also Coby’s excellent site – it’s much appreciated.

  33. 33
    Mark A. York says:

    It is excellent and I have used some of the points in my anti-Crichton novel.

  34. 34
    Rick says:

    Good and useful site, Coby Beck. Where DO you get your energy?

    Thanks, Rick

  35. 35
    Coby says:

    Dragon’s Flight,

    Those are some beautiful graphs, it looks like just about all my favorites are your work. As for requests, I would like to see a models vs observations 20th century with some appropriate smoothing, eg the last or all of the plots here:
    http://www.grida.no/climate/ipcc_tar/wg1/fig12-7.htm smoothed perhaps to a 5 yr mean like the red line on the GISS analysis. People still look at the non-smoothed ones and note where a particular year is off by as much as .5oC, silly as that observation may be. Actually I see one that has that in it:
    http://en.wikipedia.org/wiki/Image:Climate_Change_Attribution.png maybe that’s the one I want.

    Very nice stuff!

  36. 36
    Coby says:

    To all:

    Thanks very much for the encouraging and complimentary words. WRT corrections, comments at the article in question are probably the easiest for me, I will just delete them after fixing the problem. If it is easier (ala the proof reading offer from Leonard, #21) to email a bunch at once that is much appreciated, use (remove #Space “coby 101 @ gmail . com”). I will be discussing the wiki approach offered in #1 once some of my deer-in-the-headlights feelings subside…

  37. 37
    mark says:

    I’ll need a little more than a graph.

    Seems there is a volume of literature indicating that the temp did drop more than a degree C.

  38. 38
    egbooth says:

    Hi guys,

    What are contributor’s opinions on Vladimir Shaidurov of the Russian Academy of Sciences. EurekAlert just posted an article on his theory that the Tunguska Event caused recent global warming. Here’s the link to the article:
    http://www.eurekalert.org/pub_releases/2006-03/uol-gts031306.php

    Interested in hearing what you think. Perhaps another post could address this as it seems like some media outlets will definitely quote this article.

    [Response:Sounds pretty nutty, but eerily reminiscent (minus the meteorite) of some aspects of Fred Hoyles theories of ice ages - William]

  39. 39
    mark says:

    hmmm, Tambora…1816

    http://en.wikipedia.org/wiki/Year_Without_A_Summer

    or 92 being the coldest year on record, along with 1915…?

    [Response: "92 being the coldest year on record". Hunh? You need to take a more careful look at the CRU global surface temperature record you were referred to once already. As for 1816, its one of the best examples of precisely the point that has been stressed by us previously with regard to the essential distinction between regional and hemispheric/global anomalies: "See e.g. our review paper (Schmidt et al, 2004), where the response of a climate model to estimated past changes in natural forcing due to solar irradiance variations and explosive volcanic eruptions, is shown to match the spatial pattern of reconstructed temperature changes during the "Little Ice Age" (which includes enhanced cooling in certain regions such as Europe) as well as the smaller hemispheric-mean changes." - mike]

  40. 40
    Coby says:

    Re #36

    mark, you were pointed to a global temperature analysis but you have only provided your own assertion. It seems like the ball is in your court, no?

  41. 41
    Coby says:

    #33 Thanks for the Wikipedia reference. Seems we are talking about a regional effect here.

  42. 42
    Hank Roberts says:

    I wonder if that’s a refereed journal?

    The Tunguska effect on stratospheric clouds needs a magnitude — to factor in compared with the known forcings and feedbacks.

    I do recall reading somewhere that more stratospheric clouds are being seen at lower latitudes in recent decades (Great Britan has published some nice photos) — but do we have a historical (or artistic!) record of them occurring so far south before Tunguska?

    I wonder whether Tunguska’s effects could have been much greater than those of all the anthropogenic large/high-altitude airbursts we have on record in the last fifty years or so?

    http://www.johnstonsarchive.net/nuclear/tests/index.html

    I think I recall the amount of water injected into the stratosphere by jet aircraft in each of the last three or four decades amounts to something like a quarter the amount injected by natural processes.

  43. 43
    Hank Roberts says:

    Further – estimates vary but suggest a Tunguska-scale (12.5 megatons) event happens about once every 100-300 years; nice summary from sci.space here:
    http://www.totse.com/en/technology/space_astronomy_nasa/tunguska.html

    Description with several paintings, basing pictures on witness reports:
    “… estimate is that the Tunguska had an explosive energy roughly on order of 60 A-bombs, or 500 KT of TNT. It was closer in effect to a very large H-bomb.”
    http://www.psi.edu/projects/siberia/siberia.html

    Here’s a trace of it:
    “… a pulse of cosmic iridium has been reported to coincide with the 1908 Tunguska impact event. It is likely that many events of Tunguska magnitude should be preserved in a deep ice core….”
    http://www.gisp2.sr.unh.edu/NOTEBOOKS/Notebook2.html

    I doubt there’s a good proxy for the presence or absence of noctilucent clouds, except the art museums!

  44. 44
    llewelly says:

    In reply to Mark and his insistence about the effect of Krakatoa.

    I’ll start with this graph of radiative forcings. Scroll to the bottom. The bottom graph is of volcanic radiative forcings, in Wm-2. Negative values cause cooling. Notice the downward spikes are all very narrow. The cooling effects are short lived. This paper by Alan Robock seems to give a reasonable (to me, but I am neither a climatologist nor a vulcanologist) explanation of how volcanoes affect climate. Robock claims cooling effects of volcanoes last 1-3 years. Next, compare graph 6.8 (d) to the graph at the top of the same page, 6.8 (a). Notice the sustained upward trend, which becomes very strong, particularly after about 1970. The volcanic cooling effects may occasionally be larger in magnitude, but they are very short lived.

    Using the years of eruption from table 1 in the previously linked Robock paper, a few of the downward spikes in 6.8 (d) are easily associated with major eruptions. Pardon me for ignoring the many minor eruptions which also contribute to these spikes. The biggest – at about 6.4 Wm-2 – is Tambora, in 1815, responsible for the Year Without a Summer. Next biggest is probably Krakatoa , in 1883. There is some disagreement at about 1982, when El Chichon erupted. Robock’s reconstruction has El Chichon (and other lesser volcanoes) causing a much stronger radiative forcing than Sato’s. Robock’s has El Chichon stronger than Krakatoa, but Sato’s has it weaker. Since they agree on Krakatoa’s radiative forcing, I take Krakatoa to be the second biggest. The far right spike I take to be Pinatubo‘s 1991 eruption, with some addition from Hudson‘s 1992 eruption. Two other spikes – probably Cosiguina, Nicaragua, 1835, and Katmai, Alaska, 1912, are similar in size to the Pinatubo spike. Note this usgs page has some information about weather-affects of volcanoes that I have not covered here. (It says nothing about Krakatoa, however.)

    It seems to me there are about 6 downward spikes in the volcanic radiative forcing that are of magnitude comparable to or greater than that recently reached by well-mixed greenhouse gasses (WMGG). Again, compare 6.8 (d) to 6.8 (a) . Tambora 1815 and Cosiguina 1835 predate the instrumental global temperature record , and are hard to pick out on a 1 kyr reconstruction. Tambora is widely reported to have lowered global temps by as much as 3 C. However, in the above linked 1 kyr reconstruction, it looks to me like the 1815 global temp dip is only about 0.2 C. (Although the dip appears, and looks about the same size, in most of the reconstructions in the graph, it is smaller than the differences in the reconstructions.) I take this to mean that even the effects of Tambora, a much larger eruption than Krakatoa, were too short lived to be accurately captured by such reconstructions, and therefor, too short lived to have much effect on long-term trends. A year without a summer, ruined crops in New England and Europe, but it nonetheless had little significant effect on long-term trends. Krakatoa seems similar, but smaller. 1.2 C of global cooling appears to be widely reported, but the seemingly associated dip in instrumental global temperature records is maybe 0.1 C at most. This too may be due to the effects being too short-lived to be captured by such records, but note that annual averages do not appear to capture any larger a dip after 1883 than the 5-year smoothed averages. (I can’t help but wonder if 1.2 C is simply over-reporting of the most exciting number – perhaps the top end of a range of uncertainties, or research that was later rejected?) The downward spikes in radiative forcing which I associate with El Chichon and Pinatubo also seem to appear to have very small and short-lived effects.

    The cooling effects of volcanoes appear so short lived I am tempted to suggest a Krakatoa a decade would be required to counteract human-induced global warming. That seems unlikely …

  45. 45
    C. W. Magee says:

    Mike, and other people loooking for short-term alterations in the 1000 year temperature record:

    You need to read the methods of the papers to see how the data has been processed to form the lines shown. As an example, the data in line number 6 has been smoothed: “Each regional temperature record was standardized by removal of the long-term mean and division by the standard deviation after decadal smoothing (lowpass filtering at f = 0.1 cycle/year).” (Mann & Jones 2003).

    Looking for any climactic events that operate on a time scale shorter than the smoothing is sort of a waste of time.

    -Chuck

  46. 46
    Armin says:

    I doubt there’s a good proxy for the presence or absence of noctilucent clouds, except the art museums!

    I think you are confusing polar stratospheric clouds (PSC) with noctilucent clouds (NLC) here. Noctilucent clouds have been first reported in 1885 (Jesse, Meteorol. Zeit.; Leslie, Nature). People working on the field (including colleagues at my institute are pretty sure that they did not exist before as there was an International Polar Year in 1882/83 which did not report them.

    Although a connection to the Krakatoa eruption is often quoted for the appearence of noctilucent clouds, there is no convincing proof of the exact connection of these two events.

    About polar stratospheric clouds, I can’t tell you much. Maybe someone else knows more.

  47. 47
    Tom Rees says:

    Dragonsflight, regarding plots of sea level rise. I haven’t read Church’s paper so I haven’t been able to see for myself. Which is why I was hoping you’d make a plot :) But I believe it’s the most authoritative amalgamation of topex/poseidon and gauge data to date. I think gauge data after calibration to poseidon is likely to be more realistic.

    Also, while we’re on the topic, what about quaternary sea level. The sea level calculated by Shackleton from Vostock d18O data doesn’t show too good correlation with ice ages (from visual inspection, I know his calculation of the phasing comes out right). Are there better sea level data from this period. I have seen some in a recent presentation by Hansen Slide 16 or thereabouts that are quite different.

  48. 48
    Pete Best says:

    I know that this is slightly off topic but the recent readings of the thermohaline system in the atlantic seems to be telling us the evaporation at the equator has increased thus causing the upper layers of the Ocean to increase in salinity whilst the northern Atlantic waters are becomming fresher due to increased rainfall from precipitation. This increased salinity vs increased freshness is causing the thermohaline system to speed up thus carrying more heat (is this possible ?) from the equator to the poles and hence bringing about its slow demise.

    Could realclimate comment on this at all and state whether it is possibly true ?

  49. 49
    SteveF says:

    Slightly off topic and I may have mentioned this before, but methinks a review of Carl Wunch’s latest in Quaternary Research would make for a valuable contribution to the site. Not exactly convinced by wind fields, but it is an interesting contribution. I wonder how many other big ideas in palaeoclimatology he is going to go after!

  50. 50
    Lawrence McLean says:

    Re #31
    Mark,
    volcanic eruptions produce about 110 million tons of CO2 each year.
    Human activities contribute almost 1,100,000 million tons of CO2 each year.


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