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What we can learn from studying the last millennium (or so)

Filed under: — mike @ 15 May 2010 - (Español)

With all of the emphasis that is often placed on hemispheric or global mean temperature trends during the past millennium, and the context they provide for interpreting modern warming trends, one thing is often lost in the discussion: space matters as much as time. Indeed, it is likely that the regional patterns of past climate changes, rather than simple hemispheric or global mean temperature trends, will best inform our understanding of the dynamical mechanisms involved. Since much of the uncertainty in future projections relates to regional climate change impacts, it makes particular sense to focus on those changes in the past that involve regional changes and the underlying mechanisms behind them.

For instance, melting of the cryosphere (and consequent rises in sea level), subtle shifts in drought and rainfall patterns, and extreme events, are all regional effects that could be important threats to ecosystems and our environment. Such changes are often associated with phenomena like ENSO or the North Atlantic Oscillation. Yet there remain large uncertainties about how such mechanisms will respond to anthropogenic climate change.

There are a number of potential ways forward to improve our understanding. A first step is to look directly at the time-series of specific systems (like the ENSO index or the ocean temperatures in the North Atlantic) and try to extend them as far back as possible using proxy data. This gives more information on what the natural variations in these phenomena look like, and thus a better idea of how big a forced response would need to be before it could be reliably detected. Secondly, we can look to see if there is a relationship between various natural drivers of climate change (volcanic eruptions, solar variability or orbital forcing say) and any characteristics of these phenomena – amplitude, frequency or duration. Do volcanic eruptions appear to affect El Niño for instance?

For phenomena that need annual or decadal resolution data to be resolved, the last millennium or so is an obvious (and only) time period to be looking at for it is only for that period that there is sufficient paleo-data coverage of high enough temporal resolution. Other periods – such as the mid-Holocene 6000 years ago – are also useful, but the results are more long-term in nature (there is also a discussion of the value of different periods for reducing future projection uncertainty in this recent paper).

There are a number of different approaches to looking at reconstructions in recent centuries – some rely on high density regional networks (as seen in this recent paper by Guiot et al concerning European temperature trends for which they mostly used pollen data) and some rely on wider networks of more diverse proxies which aim to capture longer-range correlations to specific phenomena (such as the recent Mann et al (2009) paper).

When this is done, people usually find that while it was relatively cool in global mean temperatures from the 1400s to the 1800s known as the “Little Ice Age” and relatively mild in the 900s to 1300s interval ( sometimes termed the “Medieval Warm Period”). But the spatial reconstructions reveal, however, why such global terms can be quite misleading, and why alternative phrases such as the “Medieval Climate Anomaly” are being increasingly favored by the community. This latter terminology recognizes that while the interval displayed significant climate anomalies, they varied greatly, even in sign, from region to region. Many of the more profound climate anomalies, moreover, involve variables other than temperature, such as drought, rainfall, and atmospheric circulation. Though the medieval period is seen to be modestly warmer globally in comparison with the later centuries of the Little Ice Age (the peak global mean warmth is likely comparable to mid, but not late, 20th century warmth), some key regions appear to have in fact been colder, while other regions appear to have been warmer. Southern Greenland, for example, appears within uncertainties to have been as warm as today. However, much of the tropical Pacific was unusually cold, suggestive of the La Niña phase of the ENSO phenomenon (a similar conclusion was reached by Trouet et al (2009)). Thus even though some locations may have been as warm or warmer than today, the hemispheric mean appears not to have been.

Why does this matter? It matters because there are plenty of factors that can affect the overall mean temperature (solar variability, volcanoes, greenhouse gases, internal variability etc.) and so it is hard, given the uncertainties in the solar or volcanic reconstructions to precisely attribute the paleo changes in the global or hemispheric mean to these factors. But if we can look at more complex fingerprints of the changes, it might be possible to be more quantitative in those attributions since the spatial fingerprints of the different factors are easier to distinguish. Furthermore, if we can clearly tie the regional patterns to the different forcings, we might be able to use that information to inform regional projections under future conditions.

Thus we can basically say that the warmer conditions of the Medieval era were tied to higher solar output and few volcanic eruptions and the cooler conditions of the Little Ice Age resulted from lower solar output and more frequent volcanic eruptions. But these drivers appear to have had an equally important, though more subtle, influence on regional temperature patterns through their impact on climate phenomena such as ENSO and the North Atlantic Oscillation. The modest increase in solar output during Medieval times appears to have favored the tendency for the positive phase of the NAO, associated with a more northerly jet stream over the North Atlantic. This brought relatively greater warmth in winter to the North Atlantic and Eurasia. A tendency toward the opposite negative NAO phase helps to explain the enhanced winter cooling over a large part of Eurasia during the later Little Ice Age period.

There is some model support for these patterns (see also instance Shindell et al, 2001) when the models include interactive ozone photochemistry to produce this dynamical response to solar forcing, but it is not captured in a simulation of the NCAR CSM coupled model which lacks those processes. Neither model simulation reproduces the apparent La Niña pattern seen in the Medieval temperature reconstructions:

Figure 1: Spatial pattern of mean temperature difference between the MCA and LIA periods (defined at the intervals AD 950-1250 CE and 1400-1700 CE respectively) compared with simulations of two different climate models forced with estimated differences in natural (volcanic and solar) radiative forcing between the two periods (Mann et al, 2009).

Other model simulations, however, using a climate model that exhibits a particular tropical Pacific mechanism, do reproduce such a response. In such models, the tropical Pacific counter-intuitively tends to the cold La Niña phase during periods of increased heating, such as provided by the increase in solar output and low volcanism of the Medieval era. If this response holds for the future, something that is still vigorously debated, it could imply a more La Niña-like response in the future. Most of the state-of-the-art climate models, e.g. those used in the IPCC Fourth Assessment, by contrast, suggest the opposite–a more El Niño-like future climate. The credibility of the models with regard to this phenomenon is not high, however, and lots more work is going to be needed (both on paleo-reconstructions and model improvements) before we can be confident in the future projections of changes in ENSO-like dynamics and mean state.

690 Responses to “What we can learn from studying the last millennium (or so)”

  1. 351
    Jason Miller says:

    #349 – Hank Roberts

    Thank you for posting the links above and clearing up my confusion. I had not heard about this.

  2. 352
    sidd says:

    Mr. Jason Miller says on the 21st of May 2010 at 7:48 pm

    “…maps, one of which is of Antarctica. I placed the 1998 and 2010 page sized maps side by side and did a comparison”

    I must recommend this exercise. I have on my wall, a world map published by the Defense Mapping Agency of the USA in 1975. It includes the summer and winter sea ice extent lines as they were then, many ice shelves that no longer exist, a non shrunken Aral Sea…

    It is quite shocking to compare that map with the reality today.


  3. 353
    Doug Bostrom says:

    Anand says: 21 May 2010 at 6:22 PM

    Saturation? That argument is an anachronism, put in its grave some time ago right here at RC among other places.

    Yet another volunteer supplied with yet another comic rubber chicken to wave about. Demand a better prop; those folks meeting in Chicago are paid to freshen their act from time to time.

  4. 354
    John Mashey says:

    re: #350
    Anand :
    1) Can you cite which of Happer’s papers you think are relevant, and explain why?

    2) I watched Happer (not a biologist) explain why polar bears will be just fine and (not a coral expert) explain that ocean acidification wont’ bother corals.

    3) As I suggested in #345, do you yet understand the nature of GMI?
    If you don’t want to read what I suggested, in just a few days, Merchants of Doubt, by Naomi Oreskes and Erik Conway, will be available, and you can read that.

    Happer’s predecessors in that job were experts, so he had good trainers.

    You might want to read The Daily Princetonian’s interview with him. That’s the one that quotes him:
    “This is George Orwell. This is the ‘Germans are the master race. The Jews are the scum of the earth.’ It’s that kind of propaganda,” Happer, the Cyrus Fogg Brackett Professor of Physics, said in an interview. “Carbon dioxide is not a pollutant. Every time you exhale, you exhale air that has 4 percent carbon dioxide. To say that that’s a pollutant just boggles my mind. What used to be science has turned into a cult.””

  5. 355
    Lawrence McLean says:

    Re #344 Anand,
    It seems to me that to say the atmosphere is saturated with CO2 is a silly thing to say! Something obvious: the atmosphere declines in density with altitude. What this means is that even if CO2 was saturated (in terms of radiative effect) at sea level it will not be at some altitude above sea level. If I am wrong please let me know.

  6. 356

    #348 Hank Roberts

    Re. Jason Miller #346

    Thanks Hank :)

    Jason, it may be that you were looking at data or images from Antarctic minimums for southern hemisphere at max melt?

    Remember, context is key.

    A Climate Minute The Greenhouse EffectHistory of Climate ScienceArctic Ice Melt

    ‘Fee & Dividend’ Our best chance for a better future –
    Learn the Issue & Sign the Petition

  7. 357
    Jacob Mack says:

    Also an interesting article. Let me know if the link does not work, as there is free access online:

  8. 358
    Completely Fed Up says:

    jacob mack says:
    21 May 2010 at 5:24 PM

    CFU try reading the IPCC report”

    And what am I going to read there except that AGW causes, globally, warming? Which is what I’ve been saying and you’ve been refusing to accede.

    Why try to throw me on a wild goose chase when you refuse to answer my rather simple queries?

    Because you don’t like the idea that we are being affected by climate change, though you’ll admit (if you have to) that there is climate change going on. Just not in any one event.

  9. 359
    Completely Fed Up says:

    Ibrahim says:
    21 May 2010 at 4:21 PM”

    Go to the Start Here page. Or


  10. 360

    Gilles 309: Very honestly, if I didn’t read newspaper, I would have never thought there is a climate change at all. I have travelled all around the world, I’ve seen very different climates, and I do not know any place where the climate has changed following the usual taxonomy ( arctic, oceanic, continental, tropical, and so on…, or more precisely for instance the Köppen climate classificationöppen_climate_classification ).

    And this simply because I do not know any place in the world where “changes” have exceeded significantly ( statistically speaking ) the known natural, preanthropogenic, local variability.

    BPL: As a French citizen, you may not know about the imported Chinese vine, kudzu, which has devastated much of the American southeast for the past century or so.

    It has now been reported in Pennsylvania, New York, Maine, and Ontario.

    Look at a map to see why that indicates climate change.

  11. 361

    Ibrahim 340,

    Mt. Pinatubo depressed world temperatures by about 0.3 K for two years.

  12. 362
    Ray Ladbury says:

    Anand, Happer’s expertise is atomic and molecular physics, not climate or atmospheric physics. His thinking on the matter is quite shallow, actually, giving no indication that he has ever undertaken serious study of climate.

    Lindzen is another matter. He has fallen in love with the idea of strong negative feedback giving rise to an ultra-stable climate–despite there being no evidence in favor of the idea and plenty of paleoclimatic evidence against it. Why he has fallen in love with the fallen idea, I do not know. Some of his writing on the subjece gives an impression that he believes in the strong anthropic principle.

    Lindzen is worth listening to. He is still trying to play the game–although his rejection of CO2 as a climate driver makes it very difficult for him to contribute. Happer is talking out of an alternative orifice.

  13. 363


    Yes, carbon dioxide is a natural component of the atmosphere.

    So is nitrogen. In fact, nitrogen is the main component of the atmosphere. Like carbon, it is necessary to many life forms. The latter point can be made about phosphorus, which, like carbon dioxide and nitrogen, can act as a fertilizer–and, like nitrogen in fact, is sold commercially for precisely this purpose.

    None the less, nitrogen and phosphorus can act as a pollutant when present in excessive quantities in the wrong places. You could make analogous points for NaCl, too, and I’m sure for other substances.

    So why do folks like Happer–who presumably should know better–want to treat CO2 differently than these other natural-and-necessary-substances-which-nevertheless-can-pollute?

  14. 364
    John E. Pearson says:

    332: Thanks Hank. Excellent thought.

  15. 365
    Bill Ruddiman says:

    There is still at least one fly in the ointment regarding natural explanations of the MWP/LIA cooling. That view says or implies that a natural cooling drove the observed CO2 drop (~10 ppm) from ~1200 to 1700. Estimates of the (N Hem) cooling over that interval range from ~0.2C (Mann) to ~0.5C (Moberg). Carbon-climate models suggest that the sensitivity of CO2 to temperature forcing is around 10 ppm per degree C. The model estimates range widely, but that seems to be the consensus number. If so: the estimated cooling can explain a CO2 decrease of about 2-5 ppm out of the 10 ppm observed.

    The same problem arises for the interval 1500-1650. The estimated cooling (0.15-0.4C) explains just 1.5-4 ppm out of a measured CO2 drop close to 10 ppm (and sustained at 5-7 ppm until 1750).

    So: if most of the measured CO2 response was not natural in origin, how complete is our understanding of this interval? I said this in my 2003 ‘Early anthropogenic’ paper, but it seems to have drawn little attention, except from Nevle/Bird.

  16. 366
    Anand says:

    Mr Ruddiman:
    Your books are always checked out at the library. I hope to read them soon. ;)

    Re you CO2 sensitivity to temperature:
    Frank et al (2010) estimate gamma to be much greater (by a factor of 10) in cooling phases than in warming phases. Their estimate is in the order of 40 ppm CO2 per degree.

    [Response: Anand, why do you say this? Did we not go over this at length in the discussion at that time? There was no stated relationship between the direction of temperature change and the magnitude of gamma, and Frank et al. did NOT find a gamma of 40 ppm/degree when temperatures were cooling. Furthemore, the higher values of gamma associated with the rapid CO2 drop in the late 16th C should not really be considered as gamma values if land cover changes were in fact responsible, because gamma attempts to estimate sensitivities independent of such confounding factors. Please go back and re-read.–Jim]

    Perhaps CO2 solubility/sinks behavior in cooling phases has been underestimated.


  17. 367
    Bill Ruddiman says:

    Response to #366:

    Frank et al gave a best estimate of 8.8 ppm CO2 change per degree C, which is even lower than the 10 ppm/C that I cited, so it would explain even less of the observed CO2 drop. They do estimate a higher sensitivity (roughly a doubling) during the cooling after 1550, but they don’t explain why the sensitivity would have changed at that time. Cox and Jones, Science Sept 19, 2008 suggest a very high sensitivity like the one you mentioned for the interval 1550-1800, but again don’t say why the system sensitivity would abruptly go up by a factor of four or more compared to ‘normal’. There is a serious danger of circular reasoning here— deriving a very high sensitivity from the observed temp/CO2 trends in order to explain a CO2 drop that the normal sensitivity cannot explain. In contrast, if most of the CO2 drop is anthropogenic (the American pandemic and demographic collapse), then the normal sensitivity would still apply over that interval.

  18. 368
    Rod B says:

    John Mashey (345), is this the old ‘if you can’t refute the science conjecture, at least show that he hangs around with ugly people” argument??

  19. 369
    Jacob Mack says:

    CFU spewed: “CFU try reading the IPCC report”

    And what am I going to read there except that AGW causes, globally, warming? Which is what I’ve been saying and you’ve been refusing to accede.”

    I have always stated that AGW increases global warming. Or, in your language causes new warming that is NOT due to natural variations. You have no evidence to support this claim.

    CFU: “Why try to throw me on a wild goose chase when you refuse to answer my rather simple queries?”

    No wild goose chase; some areas of drought will be worsened by AGW, some will not; some areas as Ray Ladbury stated have drought and flooding in a very short span of time. Again you are making this up CFU.

    CFU: “Because you don’t like the idea that we are being affected by climate change, though you’ll admit (if you have to) that there is climate change going on. Just not in any one event.” AGW is a fact CFU and I have stated so numerous times. Of course we are and will be affected by climate change. My only point is you are hypoer-fcoused on droughts alone, and this is a gross oversimplification of the issues of AGW.

    Prediction is still somewhat troubled and attributions range from being very statistically significant to not so much.

    Please read a little more carefully my posts and references I leave. Pay attention to Ray and Hank’s posts as well. Inferential statistics is by its very nature interpretive and probabilistic.

  20. 370
    Jacob Mack says:

    Yeah guys there is no scientific basis for saturation of CO2 in the atmosphere whatsoever, so can we get off that topic?

  21. 371
    Jacob Mack says:

    CFU: “Warmer temperatures.

    When you already HAVE a drought, is it true or not that making it warmer makes the drought more severe.

    Answer that question.

    Seems nobody reads anymore.”

    Global warming can sometimes does and will make some droughts more severe, but as the wold wams some areas prone to droughts will on average have more rainfall with inceased evapoation. Also some regional weather conditions will change, possibly cooler in some regions.

    Back to Ray’s example of monsoons and drought in Africa; this is certainly detimental as most of us agree, but not necesaaily in terms of worse doughts alone.

    p.s. AGW has both negative and positive consequences, but the majority seem to be more negative in the majority of regions. Still some polar regions along with others in North America will benefit in several ways, but desrtification is a real issue in already dy and aid climates.

  22. 372
    Rod B says:

    Jason Miller (346) Graphs from the U of Illinois show very little difference in ice extant in Antarctica — virtually zero anomaly the past 30 years, though with noticeable annual variation. These graphs have large granularity and may not readily show the changes you’re talking about. They also measure sea ice which I am assuming is what shelves are. Comment on these two points?

    There does seem to be agreement that the average temperatures around the coast of Antarctica (though not the interior and, curiously, not north into the Southern Ocean) have increased in recent decades and that ice shelves are, on the whole, losing mass. The coastal temp increase is much greater than what the average global temperature has been; it is also close to H2O freezing normally so it doesn’t take much to rise above freezing. But there is serious disagreement as to whether this is due to AGW or just regional natural variance. For example warmer Antarctic temperatures ought to increase ice mass from increased precipitation.

  23. 373
    Rod B says:

    Doug Bostrom (353) says, “Saturation? That argument is an anachronism, put in its grave some time ago right here at RC among other places.”

    For the record (my broken one to be precise) put in its grave with convenient (though maybe reasonable) hypotheses as opposed to irrefutable physics. It’s not obvious who is waving a comic rubber chicken. (Is that like a strawman???)

  24. 374
    Rod B says:

    Lawrence McLean (355), theoretically if CO2 did absorb all of the radiation in its absorption band, then no matter how much CO2 was at higher altitudes it would have no radiation to absorb. This is an oversimplification of what actually happens but does address your point in the main.

  25. 375
    David B. Benson says:

    Jacob Mack (287) — What more would you like to know?

    I realize I know of another paper which I now ought to reread to add to the three considered so far.

  26. 376
    Septic Matthew says:

    360 Barton Paul Levenson: It [kudzu] has now been reported in Pennsylvania, New York, Maine, and Ontario.

    Look at a map to see why that indicates climate change.

    That is an interesting comment. Within the last 100 years most of the American chestnuts of the northeast have died of natural causes and the remainder are severely diseased. Is there evidence that the spread of kudzu is not also due to random variation and natural selection? The stuff grows and reproduces rapidly, so spreading (as with XDR TB) is inevitable with time unless native browsers start preferring it as food.

  27. 377
    jacob mack says:

    Regarding C02 saturation, reading Spencer Weart puts the final nail in that coffin.

  28. 378
    Hank Roberts says:

    > most of the American chestnuts of the northeast have died
    > of natural causes
    False, and you can look it up

    > Is there evidence that the spread of kudzu is not also due to
    > random variation and natural selection?
    Yes, and you can look it up.

    Good grief.

  29. 379
    Hank Roberts says:

    Oh, let me correct myself; only the above-ground part of the chestnuts after five or six years old dies.

  30. 380
    Jacob Mack says:

    David B. Benson, # 375: any information and references you have would be most helpful; thanks in advance.

  31. 381
    RichardC says:

    376 Matthew asked, “Is there evidence that the spread of kudzu is not also due to random variation and natural selection?”

    Kudzu can’t take a very hard frost. A good hard killing frost would still kill off any kudzu in Maine.

  32. 382
    Completely Fed Up says:

    “theoretically if CO2 did absorb all of the radiation in its absorption band, then no matter how much CO2 was at higher altitudes it would have no radiation to absorb.”

    Theoretically, the CO2 at the higher altitudes would have the radiation from the saturated CO2 at the lower levels to absorb…

    Energy is not destroyed, you know…

  33. 383
    Completely Fed Up says:

    “Global warming can sometimes does and will make some droughts more severe,”

    So show it happened with the SE US drought.

  34. 384
    Completely Fed Up says:

    Jacob, I’ve read the IPCC.

    It seems you haven’t if you think they say that no drought has been affected by AGW…

  35. 385
    Completely Fed Up says:

    “Prediction is still somewhat troubled and attributions range from being very statistically significant to not so much.”

    Uh, show how the CO2 didn’t warm the SEUS, jacob.


    PS you’re still avoiding answering my questions.

  36. 386
    David B. Benson says:

    E. Tziperman, M. E. Raymo, P. Huybers, C. Wunsch, 2006. Consequences of pacing the Pleistocene 100 kyr ice ages by non linear phase locking to Milankovitch forcing (pdf), Paleoceanography convincingly demonstrate that very many nonlinear systems of equations are capable of approximating, rather well, a d18O compilation for the past 900,000 years. So just matching such a proxy does not facilitate the selection of one model over another in a highly robust way. I take the conclusions to imply that the use of such models says essentially nothing about the question of whether or not AGW avoided a glacial at the present time.

    The situation isn’t quite that bad in that prehaps various information criteria, AIC or BIC, might aid in model selection. Even better, I opine, would be to follow on from the use of CO2 is Crucifix & Rougier (2009) to devise a conceptual model which tracks both CO2, maybe aslo CH4 and a choice of d18O conpendium of the interval for which CO2 records are available from Antarctic ice cores. Even then answers to the avoidance question are likely to be model dependent.

  37. 387
    Doug Bostrom says:

    Hi, RodB.

    The Saturated Gassy Argument appears not to be required in order for researchers to continue producing findings consistent with hypotheses constructed without it.

    Thus it seems reasonable to conclude that while possibly not lying cold in its grave, the Saturated Gassy Argument is elsewhere and playing no active role. Possibly it is even poolside at a conference in Chicago sipping from a drink with a tiny umbrella and doing nothing while everybody else is hard at work. Yet nobody notices; its absence from duty has no measurable effect so it’s quite safe to say that the Saturated Gassy Argument is not necessary to better scientific understanding of climate and thus is irrelevant.

    Regarding rubber chickens, I’m still struggling to find exactly the right metaphor for the sort of weapons being handed to volunteers stepping forward to defend industrial interests with a need to maintain the status quo in terms of fossil fuel consumption.

  38. 388
    Ray Ladbury says:

    Rod B., you need to review:

    It is irrefutable that CO2 radiates as well as relaxing collisionally.

    It is irrefutable that absorption lines broaden with pressure and velocity.

    It is irrefutable that CO2 is a well mixed, long-loved greenhouse gas well into the stratosphere.

    Any model starts out as a series of “convenient assumptions”. Once they are verified by the predictive power of the model, they cease to be merely assumptions. It’s called science.

  39. 389

    376, Septic Matthew–

    Yes, there is evidence. The historic spread pattern correlates very well with the temperature record. If you link back on RC, you should be able to find references.

    The recent news on this topic was the publication in PNAS of Lerdau, 2010, which showed that kudzu infestation significantly raises tropospheric ozone levels in summer–enough to cause public health impacts.

    Kudzu has now been found in Canada (Leamington, Ont–where a lot of my mom’s family went to high school) and in Maine. The Canadian find was just last year, and has prompted the issuance of alerts to try and prevent the plant from becoming established.

  40. 390
    Jason Miller says:

    Mr. John P. Reisman ( 22 May 2010 @ 1:24 AM),

    I did not understand when you said “Antarctic ice extent increase” in #334 that you meant the extent of sea ice. I thought you were implying the ice shelves and glaciers were expanding, thus the subsequent post. Mr. Hank Roberts pointed out at #348 that you were referring to sea ice and provided links. I had not considered sea ice before. So yet another item has been added to the list of things I need to learn more about concerning climate change.

  41. 391

    Well, this symposium powerpoint has some pretty good analysis on kudzu & temps, too:

  42. 392
    Anand says:

    “long-loved greenhouse gas”

    I love CO2!

  43. 393

    One last kudzu link: this is the one John Mashey originally provided; it actually includes some lab work, they actually chilled/froze kudzu stems, measured tissue damage and subsequent growth if any. You can see they drew on the Ziska work linked above.

    Bottom line: I think the temperature/kudzu range link looks pretty damn solid. (As well as being eminently sensible in the first place.)

  44. 394
    Hank Roberts says:

    > Rod B says: 22 May 2010 at 2:58 PM
    > Lawrence McLean (355), theoretically if CO2 did absorb all
    > of the radiation in its absorption band

    In your theory, the CO2 would do what with all this absorbed energy, Rod?
    Tuck it away into some string theorist’s extra curly hidden dimension?

  45. 395
    John Mashey says:

    re: 376 Septic Matthew
    Back in #206, I posted a pointer to a nice presentation on kudzu by Toronto researchers. You don’t need to perform onerous research, like looking in Wikipedia or looking for research papers, that presentation ought to do it, and they actually have better maps. Hopefully, you will read that and return, saying “yes, that is convincing evidence from people who actually study it.”

  46. 396
    CTG says:

    It is irrefutable that CO2 is a well mixed, long-loved greenhouse gas well into the stratosphere.

    I assume that was a typo for “long-lived” – or have you gone over to the “CO2 is life” side, Ray? ;-)

  47. 397
    Rod B says:

    CFU (382), agreed, but that was left out of my maybe over simplification for clarity.

  48. 398
    Rod B says:

    Ray Ladbury (382), I concur with all of your statements. My assertions of the “less than irrefutable” are based on the degree or the differential of the functions.

  49. 399
    Jacob Mack says:

    CFU learn how to read please. Obviously I know AGW can affect droughts and increase the probability of worse droughts. I answered all of your questions as well. CFU, are you high or something?

  50. 400
    Jacob Mack says:

    Not every drought is made worse, yes you know that. Also some droughts are made less severe or reversed by FLOODING. Some droughts are made less severe by some moderate rain due to evaporative processes. I cannot fathom how you got from my posts that I thought NO droughts would be worse. My statement to you originally was to the effect that a drought discussion alone is getting out of hand. There are better ways to see highly correlated evidence in AGW than droughts or hurricanes at this point. Not all droughts are made worse when it gets warmer: fact. Not all droughts which may be more severe can be attributed to AGW with great confidence: fact. The IPCC report discusses more severe and frequent droughts, floods, dying crops, better growing crops, more possible farming in higher latitudes, more and larger pests threatening crops, etc, all facts.

    CFU one thing is clear to me that you have no college degree in anything and on that note I am done with this topic on droughts which you give more attention than it is due.