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Global cooling, again

Filed under: — group @ 27 October 2006

The ice age is coming, the sun’s zooming in / Engines stop running and the wheat is growing thin /A nuclear error, but I have no fear /’Cause London is drowning, and I live by the river (chorus from London’s Calling, by Strummer/Jones, 1979).

These lines rather sum up the confused media response in the 1970’s (the sun zooming in would *not* be causing an ice age; sea level rise would be associated with warming); engines stop running mixes up the oil crisis. At that time (and particularly the early to mid 70’s) climate science was ambiguous about predicting the future, although the 1975 NAS report summarised the state of the science pretty well: that we didn’t know enough to make useful predictions and needed to study more. And since that time we *have* studied more, with the result that we have some firm conclusions pointing to warming.

But, we’ve done this all before. So whats new?

Not much, but Senator Inhofe has been speaking about climate change again, and predictably enough dredged up the 1975 Newsweek article headed “A cooling world”. Which appears to have prompted Newsweek to re-examine their old article. They concede that the article was so spectacularly wrong about the near-term future but defend themselves with In fact, the story wasn’t “wrong” in the journalistic sense of “inaccurate”, which seems rather self-serving. Whilst the article does manage to reference the NAS report, it does so in a minor paragraph – the headline and most text implies cooling and severe problems with the food supply. Inhofe raises other various stories from way back (see here for more) but fails to point out that a few stories culled from over a century doesn’t compare at all with the media attention nowadays paid to global warming.

The lesson to take from this is the obvious one: not to take your science stories from the mass media if you can possibly find better sources. Which nowadays are readily available: the IPCC report for a solid review of the state of the science; and RealClimate for more topical stuff.

99 Responses to “Global cooling, again”

  1. 1
    jhm says:

    History is littered with examples of accepted scientific opinions that turned out to be utterly incorrect. Thie issue seems to be less one of veracity than having reasons to believe any particular theory. Even if global warming, in the main, turns out to be without merit, one can not reasonable deny its predictions merely because it’s “inconvenient.” If wishes were horses, and all that.

  2. 2
    Jim Cross says:

    Let’s assume, for the sake of argument, that we will not alter the climate to such an extent as to escape the glacial pattern we’ve had for the last three million years.

    I know most scientists don’t lke to engage in spectulation but I would be very interested in everyone’s best estimates/guesses -whatever you want call it – as to when global cooling will begin.

    [Response: This is answered by #10, #15 and #4. The answer is, probably 50 kyr for a real ice age – William]

  3. 3
    John Gribbin says:

    I always thought the lyric refers to nuclear winter.


    [Response: Could be, its rather hard to know. I assume it was Strummer picking up the Zeitgeist and may not have known exactly himself. I always wanted to ask, but its too late now – William]

  4. 4

    When will the next ice age begin?

    Back in the 1970s, by analogy with the sketchy chronology then available for the last cycle or two, it was plausibly argued that it would begin within a few thousand years. (Speculations that it could come sooner were based on anthropogenic cooling through air pollution, which probably did indeed have a substantial cooling effect at the time, although it was soon recognized that greenhouse gases would have a stronger effect in the long run.) See my historical essay.

    More recently, it has been recognized that each ice age cycle is different because fluctuations in the Earth’s orbit, which set the timing of ice ages, vary from cycle to cycle. An Antarctic ice core record of climate published in 2004 went back 750,000 years through a previous cycle where the orbital elements had been similar to those in our own cycle. The results confirmed elaborate calculations of orbits that indicated that the next ice age would not come naturally within the next ten thousand years or so, maybe in 20-30,000 years.

    There is unfortunately another possible answer to the question. If we reach a “tipping point” of feedback between warming and greenhouse emissions, where the Earth lurches into a state without Arctic ice, then the next ice age might be delayed far longer.

    ref.: EPICA community members (Eric Wolff et al.) (2004), “Eight Glacial Cycles from an Antarctic Ice Core.” Nature 429: 623-28. See also reports in Science (November 25, 2005): 1285-87, 1313-21.

  5. 5
    muller.charles says:

    About “nuclear winter”, is it foolish to think that aerosols released from nuclear testing in upper atmosphere have contributed to the cooling phase 1950-70 ?

    [Response: Not foolish, but wrong. I don’t have any figures to hand but have asked about this before: the effect just isn’t that big – William]

  6. 6
    Alan says:

    Re #2:

    “Let’s assume, for the sake of argument, that we will not alter the climate to such an extent as to escape the glacial pattern we’ve had for the last three million years.”

    Also for the sake of argument: I don’t think we can, since we already have.

  7. 7
    Timothy says:

    Re: 2[Jim Cross]

    I thought that was essentially the basis for the 1970’s global cooling scare:

    Look there are these glacial cycles in the ice cores. They’re probably caused somehow* by periodic eccentricities in the Earth’s orbit. Oh, it seems like we are “overdue” another ice age. Gosh, temperatures have been going down a bit for the last couple of decades. Er…

    * I don’t honestly think we know enough about the ice age onset mechanisms to be able to predict when the next ice age would have been were it not for Anthropogenic warming. The best that could be done would be a correlation with orbital dynamics, but that misses out the subtleties of the intermediate steps. I think the climate models are still too computationally expensive to have been able to run an “onset” scenario in a credible way. The most that they have done [as far as I know] is to reproduce the climate of the Last Glacial Maximum.

    Also, it’s Ruddiman’s argument that humans already altered the climate to the extent that we averted another ice age even before the onset of industrialisation.

    So [and I know you were only asking for the sake of argument], it’s less a question of whether we will alter the cliamte to escape the glacial pattern of the last 3 million years, as it is that we have already done so.

  8. 8
    natassa says:

    An’ you know what they said – well some of it was true!

    I too thought Clash were referring to the nuclear winter…

    Now, Inhofe would be so much cooler and so much more relevant had he engaged to similar topics. Oh, well.

  9. 9
    Wayne Byerly says:

    When one takes the unbroken temperature record from 1998 to 2004 from 101 US weather reporting locations, the Annual Average Temperature for these 101 locations is dramatically cooler since 1998. Adding in the Annual Average for 2005 dilutes the downward trend some, but the fact remains that every year since 1998 has been cooler than 1998. And those who are so sure global warming is increasing tell us that we are getting warmer and warmer, year by year. Ain’t so! These same people tell us that 1998 was the warmest year on record. Probably so if the record only goes back to about the 1970’s. But when you look at the long time Annual Average Temperatures back to 1900 or even further back, 1998 is only one of several unusually warm years, and looses it’s first place ranking to several other years. I’m talking about actual weather that happened, was recorded and is available for anyone to look and and analyze.

  10. 10
    Timothy says:

    As a more direct response to #2 than my previous effort, I can recommend reading RealClimates previous post on this subject [linked to in the article above under “We’ve done this all before“]. In that it appears that recent research [~2000] suggests the current interglacial, in the absence of human effects, could last for 50,000 years.

  11. 11
    Hank Roberts says:

    Someone at Newsweek has a sense of humor, probably not an editor.

    The phrase “wasn’t ‘wrong’, in the journalistic sense” seems an allusion to Pauli’s comment on a paper that it was not merely not right, it was not even wrong, as revived in Woit’s recent book.

    And someone — a Newsweek editor? — must be spinning anti-sensewise, to have jammed so much nonsense into their final sentence:
    “… society elected not to follow one of the possible solutions mentioned in the NEWSWEEK article: to pour soot over the Arctic ice cap, to help it melt.”

    Oh no?
    So where is this how you say “Arctic ice cap” now, Mr. Newsweek Editor? _ice_cap_?!

    NASA – ….. the ice covered with soot …

    Check back in 30 years if Newsweek’s still publishing for the next article, concluding

    “There was no Arctic ‘ice cap’. There isn’t even ice …”

  12. 12
    Jim Cross says:

    Re #4

    So you think we’ve already reached the point where we have permanently broken from the glacial pattern – cooling will never happen (at least any time in the next few thousand years)?

    Just asking.

  13. 13
    mlmitton says:

    Apparently this Isaac Asimov quotation is well-known, but I just discovered it yesterday. It’s excellent, and worth pointing out here just in case anyone else hasn’t read it:

    “John, when people thought the earth was flat, they were wrong. When people thought the earth was spherical, they were wrong. But if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together.”

  14. 14
    Zeke Hausfather says:

    Re #5
    As far as I understand it (drawing on my recollections of a lecture Hansen gave here at Yale a few weeks back), the actual net forcing associated with Milankovich cycles is relatively small, but it tends to trigger massive feedbacks (e.g. polar ice expanding, lowering albedo, cooling, expanding more) that “snowball” into a glacial period. Given that arctic sea ice is already set to disappear given current levels of GHGs in the atmosphere, there is little chance that this feedback will contribute to an ice age any time in the foreseeable future. Perhaps some of the Realclimate folks could provide a clearer explanation though…

  15. 15
    Hank Roberts says:

    Among the things not known in the 1970s:

    Science 23 August 2002: Vol. 297. no. 5585, pp. 1287 – 1288 DOI: 10.1126/science.1076120

    An Exceptionally Long Interglacial Ahead? — A. Berger and M. F. Loutre

    “Today’s comparatively warm climate has been the exception more than the rule during the last 500,000 years or more. If recent warm periods (or interglacials) are a guide, then we may soon slip into another glacial period. But Berger and Loutre argue in their Perspective that with or without human perturbations, the current warm climate may last another 50,000 years. The reason is a minimum in the eccentricity of Earth’s orbit around the Sun…..”

  16. 16
    Tom Fiddaman says:

    Newsweek’s correction is worse than the original. The original article reports on cooling as a speculative scientific curiousity, with grave potential implications, but clearly reports that “Our knowledge of the mechanisms of climatic change is at least as fragmentary as our data,Â�” concedes the National Academy of Sciences report. “Not only are the basic scientific questions largely unanswered, but in many cases we do not yet know enough to pose the key questions.” Admittedly the original put the more sensational cherry-picked factoids up front and ignored obvious details like the huge gap in time scales between current weather and descent into an ice age.

    Now, rather than acknowledging the modest deficiencies of the original, they’re treating it like a point prediction, and shifting the blame to some scapegoat scientists. If they had honestly appraised their own work, they would have recognized that they’d highlighted a set of opinions that were outliers. Since the scope of their research appears to have included only reading William’s web page, you’d think they’d have picked up on that. To say that In fact, the story wasn’t “wrong” in the journalistic sense of “inaccurate.” is a cop-out. The subhead, Why scientists find climate change so hard to predict, is even worse as it tars current scientists with the same brush, yet the article doesn’t address current prediction challenges in any useful way. The net result just lends credence to Inhofe’s red herring tactics.

  17. 17
    Tim Dennell says:

    This Newsweek article has taken on the status of an urban myth.

    But also in 1975 the New York Times said earth was Heating
    Scroll down to where it has the subtitle “Effect of Heat Waste”.

    The NYT notes concern over CO2 levels and fears that production of energy ‘heat waste’ will generate so much heat as to have a major climate impact. That did represent an emerging scientific concern of its time.

    In 1975 the National Academy of Science (NAS) applied for funds to “Establish a national climatic research program”.
    Some journalists went to town to try and convince readers this was important stuff. After all their job is to try and produce articles that’ll sell copies. As I’m sure their editors impress upon them.

    The NY Times 1975 article was based on the same story as Newsweek’s “Cooling world”.

    So don’t blame scientists, it was different approaches by (doubtless hard pressed) journalists.

    The Newsweek article was written by staff writer, Peter Gwynne. (Who still works as a freelance science writer and is doubtless deeply unhappy this is being dragged up after all this time. Hey ho.) It wasn’t written by a climatologist or member of the NAS.

    Nor is Newsweek’s conclusion -Global Cooling – based on any scientific paper published in a scientific journal. It certainly doesn’t cite any.

  18. 18
    Leonard Evens says:

    I am old enough to remember the 70s; I was 40 in 1973. I remember seeing articles of this kind, but they were clearly speculative in nature and without any firm scientific consensus behind them. My response was that it was an interesting idea but not one worth spending any significant time worrying about. When fears about global warming arose in the late 80s, my response was similar. It just didn’t seem plausible to me that humans could do enough to affect climate in a significant way. But as I learned more about the science behind the concerns, I became convinced pretty early that this was something to think about and try to avert. One major difference which should have been apparent even to a lay person was that fears of an impending ice age ran their course and we heard little about it after a while, but concerns about warming didn’t go away as evidence mounted. Indeed the case became stronger and stronger. In any case, the less obvious lesson of the ‘Boy who Cried Wolf” tale is that sometimes there really is a wolf.

  19. 19
    Gene Hawkridge says:

    We shouldn’t forget that a certain amount of not completely understood changes in weather patterns continue to make seeing the longer-term patterns difficult. Just because there are a few years of cooling mixed in with a few years of warming is, of course, really meaningless in trying to ascertain what climate is doing long term. Melting Arctic sea ice, shrinking glaciers, and increased rate of Antarctic ice flow, these are, I think, far more reliable and objective gauges to long-term climate trends than are local temperature measurements. Rising CO2 levels are also particularly poignant as a driving force. Recent reductions in average ocean temperatures may very well be a result of massive ice melting, and would also influence air temperatures to an extent, and thus these may counterintuitively signal the ongoing effects of global warming (in the long term). Sea level seemingly keeps rising, too, and at an accelerated rate from what it was just a decade ago.

  20. 20
    SecularAnimist says:

    “London Calling” is one of the great rock songs of all time. Thanks for reminding me of it. I wouldn’t try reading too much into it as far as climate science goes. It’s poetry, not science — one of those late 20th century apocalyptic visions like Jefferson Airplane’s “House at Pooneil Corners” (from the great Crown of Creation album) or REM’s “The End Of The World As We Know It.”

  21. 21
    Steve Latham says:

    This discussion of recent history reminds me of something I read in the 90’s. Unfortunately I’m not very good at using ‘the Google’, and I can’t find a link. There was a time when a large number of scientists opposed CO2 limitations and signed a petition of some sort. The reason wasn’t that they thought that CO2 emissions could not enhance greenhouse warming; rather, they were concerned that the uncertain climate benefits of CO2 limitation policies could not justify keeping the third world poor (and without access to fossil fuels). I believe the letter/petition was in 1994. It’s interesting to me that back then the science wasn’t attacked irrationally. The focus was on the policy, where it should have been. Ah, the good ol’ days.

  22. 22
    Coby says:

    Re #9,

    1998 was not the start of a cooling trend, it was merely a single anomalously high year due to El Nino.

    And you are equally incorrect about the time period for which 1998 (or 2005) was a record. It is for sure a 150 year record, almost definately a 500 year record, probably a 2000 year record, likely a 12000 yr record, likely a 125Kyr record.

  23. 23
    wacki says:

    wow, they linked to Connolley’s website but misrepresented it’s content. William, just curious, when you talked to them did you stress the point that these predictions where never made in peer review? They seem to portray your conversation a little differently.

    Everyone: There is a Rate this story at the end of an article. Make sure you give it a 1 star!.

  24. 24
    Ian Forrester says:

    Re #21

    Steve, there were at least four petitions put out in the 1990’s. They are the Heidelberg petition , the Oregon petition, and two Leipzic Declarations. They are completely bogus and were put out by the usual supects Singer, Seitz et al. The Heidelberg petition did not argue against climate change, though it is sometimes presented as though it does. It called for honesty in using science to solve and describe environmental problems. So ironic that the publishers used it so dishonestly.

    Ian Forrester

  25. 25
    S. Molnar says:

    “The lesson to take from this is the obvious one: not to take your science stories from the mass media…” William, I think you’re being much too cautious here. It’s obvious to me that you should not believe any stories from the mass media, although I admit that I haven’t restricted my sampling to your single example.

  26. 26
    Eli Rabett says:

    One of the implicit points in the frequently pointed to graphs from the various Hansen et als, which is explicitly stated in many of the same papers and Hansen’s presentations is that we are entering (indeed are already in) a state where there can be no ice ages.

  27. 27
    Robert Wagner says:

    Discussion by itself is worthless, if we wait to take action until the signs are evident (like pollution today), we miss our oppertunity to avoid what our children WILL have to deal with.

  28. 28
    Jim Cross says:

    Re: #4, 6, 10,15

    Thanks to everyone who responded to my invitation (Post #2) to speculate on when global cooling might begin.

    Regarding post #15, I’d love to read the â��An Exceptionally Long Interglacial Ahead?â�� article. Is it posted anywhere that doesn’t require membership or subscription?

    I find it rather odd that most put global cooling very far in the future or, perhaps, never happening at all. We have had three million years or so of a somewhat regular pattern of cooling and warming. The interglacials have typically been about 10k years. We’ve been in this interglacial about 11.5k years. No one seems to understand exactly how the astronomical influences, which seem fairly certain to exist, are augmented to produce the magnitude of the heating and cooling effects. Yet some seem to think we’ve stepped outside of history because of a few extra ppm of CO2 in the atmosphere. Well, maybe we have. Or, maybe the extra CO2 is driving us ever faster to a tipping point not understand at this point that leads to global cooling.

    For my own speculation, I’ll invoke Gott’s Principle. If we are 11.5k years into this interglacial, we can be 95% certain it won’t end in less ~300 years and 95% certain it won’t last longer than ~450,000 years.

    [Response: The interglacials have typically been about 10k years – simply repeating this won’t make it true. Look at, for example, . Can you spot the regular 10kyr interglacials? But this is a case where we have theory to guide us, based on the orbital variations, which is better than relying on extrapolating past cycles – William]

  29. 29
    andrew worth says:

    Would someone up on the maths care to comment?

  30. 30
    Steve Latham says:

    Thanks Ian (#24), but it was much more specific than either the Heidelberg Appeal or the World Scientists’ Warning To Humanity (suggesting that it was a bit later than ’92). Maybe it was just a letter from a few people, but I thought it would be something big enough that I would be able to find it again.

  31. 31
    AspiDJ says:

    I totally agree with the thought that discussion of climate change, whether it is cooling or ‘warming’ is worthless – unless we act on it NOW! If we keep only discussing we are going to miss the bus at probably the last chance to save planet earth.

    Scientific theories and statistical data on temperature variations and global warming are important. However what are we seeing? What is the common man actually experiencing in terms of climate variations? Across the Globe summers are turning warmer, winters milder, ice caps and glaciers are melting and the oceans are rising; and this can be seen and experienced by the common man in Canada, Europe, India and the far corners of far-east.

    We are polluting our atmosphere, like never before, with fossil fuels and toxic emissions and if we don’t control this now it will be too late! Each one of us has our individual responsibility to ACT NOW and minimize polluting the atmosphere and clean up the environment.

  32. 32
    William Astley says:

    When will the next ice age begin?

    Re: #4 and similar comments which repeat the erroneous belief that there is no concern with the abrupt start of the next ice age, due to insolation similarities of the current period to ice age cycle 11.

    The following is justification as to why there is a real concern with a sudden start to the next glacial cycle.

    In the 1990’s paleoclimatologists’ discovered evidence in the Greenland ice sheet core data that the periodic 200yr, 500yr, 1500yr, 8000yr, etc. climate changes (up to 20C drop in the Greenland ice sheet temperature) were rapid not gradual events. For example, the Greenland ice core data shows that the Younger Dryas cooling event occurred in a 5 year period (Younger Dryas is the name for a climate change from the current interglacial Holocene, warm period, back to the Wisconsin glacial, cold period, that occurred 12,800 yrs ago).

    The Greenland ice core finding was not expected (the old consensus belief was that climate changes were gradual) and many at first stated the planet’s climate could not possibly change that rapidly. (The doubter’s suggested that the ice core data was flawed.) A second Greenland ice core was drilled. The second set of ice core data corroborated that the changes were very, very, rapid.

    The question is now not did the Rapid Climatic Change Events (RCCEs) “Rickies” occur, but rather what is causing them? What are the forcing function(s) that could possibly cause such a rapid and extreme change in the planet’s climate?

    Broecker suggested that the “Rickies” such as the Younger Dryas could be due to a sudden stoppage of the thermohaline conveyor. Broecker hypothesized that a sudden release of ice sheet melt water down the St. Lawrence River, rather than the Mississippi River caused an abrupt stoppage of the thermohaline conveyor and that the stoppage of the conveyor caused the Younger Dryas. Later evidence showed that Broecker’s hypothesis was not correct. Paleoclimatic data shows that ice sheet melting has very low for 1000 yrs before and after the Younger Dryas and that the St. Lawrence River flow was lowest during the period of the Younger Dryas. Beside the problem of what could possibly cause the sudden stoppage of the thermohaline conveyor, there is the problem as to why would the hypothesized change of flow from the Mississippi River to St. Lawrence River, occur periodically. Finally, climate simulations and fundamental climatic reasoning shows that the affect on the Northern Hemisphere climate due to the stoppage of the conveyor is not sufficient to account for the observed change. It is fortunate, that a stoppage of the conveyor is not catastrophic (2C expected drop in European winter temperatures and possible winter freezing of the Baltic Ocean) as there is evidence that the conveyor flow has reduced by 30% and may stop in the near future. (It did briefly stop Nov. 2005).

    Another hypothesis as to what could be causing periodic rapid changes to the planet’s climate is that there are periodic solar events which affect cloud formation. The solar hypothesis is currently being investigated.

    [Response: This is badly garbled. In particular, no-one has seriously suggested solar forcing to explain the rapid climate changes in the last glacial – William]

  33. 33
    Rod Brick says:

    for Steve, #30, et al. You’re probably thinking of the referenced Oregon Project aka “The Petition Project”.

    It had some minor credibility problems, mostly automatic ad hominems from the folks who didn’t like the 17,000 or so scientists (predominately) who expressed doubt with GHGs causing global warming. [Though the same folks are fully supportive of the 1200 or so (mostly) politicos who put out the IPCC reports.]


    While our earth may be heating up disastrously (I personally doubt it, but I might be wrong… and what do I know??) I think the science verdict is still out irrespective of the near-manic pep rally going on by the proponents. I think its potential risk demands an even greater full-fledged scientific investigation, and, btw, one that considers the “aginers” rather than dissing them out of hand as “outlyers”. But to cost our economies probably $40 trillion to fully implement Kyoto because some ‘don’t like the pollution’ is a bit of a stretch. It’s possible that this fully accepted theory might prove utterly incorrect like so manay before, as jhm (#1) points out. The risk still warrants spending lots (more) bucks on research, but not utterly destroying the economy.

    [Response: A better ref for the Oregon petition is You’re wrong about the economics, but we avoid that here anyway – William]

  34. 34
    Hank Roberts says:

    >15, 28
    When you can’t find something with Google, try Google Scholar; view html, view the related links — you may find the actual article; you’re sure to find enough quotes from it and citations to it to get the information.–+A.+Berger+and+M.+F.+Loutre

  35. 35

    The Pacific Decadal Oscillation � An Observed Phenomenon in Global Climate and Pacific Ecology with Implications for Flooding and Drought in Australia.

    Global temperatures of the 20th century showed a warming phase to the 1940�s, a cooling phase to the 1970�s and renewed warming to 1998. The Pacific Decadal Oscillation (PDO) is mainstream science, can explain some of the observed warming and has significant implications for flooding and drought in Australia.

    Figure 1: Global Surface Temperature Anomalies (Source: Goddard Institute for Space Studies)

    In the past century cool PDO regimes prevailed from 1890-1924 and again from 1947 to 1976, while warm PDO regimes dominated from 1925 to1946 and from 1977 to 1998.

    Figure 2: October-to-March averaged PDO indices. Positive values indicate warm phases of PDO, while negative values indicate cool phases of PDO. Solid curve shows a 5-year running average for each time series. (Source: Joint Institute for the Study of the Oceans and the Atmosphere)

    The Pacific Decadal Oscillation (PDO) is a natural climate phenomenon that has been traced back in trees and coral for more than 400 years. The divergent climate states were first discerned in arctic fisheries in 1996 but have since been discovered in changing abundances of anchovies and sardines in Monterey Bay (having given rise to John Steinbeck’s novel Cannery Row) and in Australian multi-decadal rainfall trends.

    Australia has good flood records going back more than 100 years. It has been known for some time that Australia experiences decades long periods of drought and, alternatively, decades long periods of flooding. Recent flood analysis suggests that the phenomenon is a result of long term modulation of both the frequency and intensity of La Nina and El Nino events in the El Nino Southern Oscillation (ENSO).

    An effect on global temperatures should be anticipated from a phenomenon that involves the ENSO. More frequent and intense El Nino leads to higher global temperatures � as seen in the last warm phase of the PDO. Conversely, more frequent and intense La Nina in a cool phase of the PDO results in lower global temperatures.

    Beginning to disentangle the PDO effects from other climate forcings in the temperature record requires consideration of a full cool/warm cycle from 1947 to 1998. The resultant trend in temperature increase is 0.07 degrees C per decade rather than the 0.2 degrees C trend obtained from consideration of the last warm phase alone. This is a significant moderation of the warming trend.

    The PDO index moved into negative territory after 1998 � but has since settled back into the positive. Global temperatures have not increased since 1998 suggesting that the effect of a cool phase of the PDO is being felt. If so, the effect will last for decades and will moderate global warming. The cyclical nature of the PDO with a period of 20 to 30 years over a long time strongly suggests, if history remains any guide, that a phase shift is likely in the near future if it has not already occurred.

    The powerful climate signal of the PDO is not included in the climate models because, quite simply, there is no agreed explanation for the observed phenomenon. This is a current limitation of the models when confronted with, as yet unexplained, real world climate variations occurring over periods of decades to millennia.

    The implications of a cool phase of the Pacific Decadal Oscillation include a decades long and large increase in rainfall, cyclones and flooding in eastern and northern Australia.

    As the Joint Institute for the Study of the Oceans and the Atmosphere says, from â��a societal impacts perspective, recognition of PDO is important because it shows that “normal” climate conditions can vary over time periods comparable to the length of a human’s lifetime.â��

  36. 36
    William Astley says:

    Re: Comment 32 which outlines the issue of Rapid Climatic Change Events, RCCEs.

    Reviewer’s Comment: “In particular, no-one has seriously suggested solar forcing to explain the rapid climate changes in the last glacial.”

    There is currently no accepted explanation as to what is causing the observed periodic rapid climatic change events, throughout the last and past glacial periods. Solar variance is most certainly on the short list of suspects. The following is an excerpt from M.Christl et al’s (2004) paper in the Journal of Atmospheric and Solar-Terrestrial Physics, which explains how the sun could affect the earth’s temperature:

    “A leading candidate to explain the link between relatively feeble solar fluctuation and climate is the effect of solar (magnetic) modulated galactic cosmic rays (GCR) on cloud formation (Editors of science, 2002). … their contribution to the global radiation climate forcing is estimated to be about -28 W/m^2 (Hartman, 1993). This is one order of magnitude larger than the radiative forcing caused by the anthropogenic greenhouse gases (IPCC, 2001).

    The observed rapid climate change events, “RCCEs” are becoming stronger based on a significant increase in atmospheric dust in both the Antarctic and Greenland ice cores during the last glacial period, as compared to past glacial periods. For example, see figure 1, “Dust (ug kg-1)” from the EPICA Dome C Ice Core, from the article “Eight glacial cycles from an Antarctic ice core”, which was published in the June 10, 2004 issue of Nature.

    [Response: This has nothing at all to do with rapid change during the last glacial. And there is no consensus on them being periodic. If there was a strong solar signal in climate, then you would need something like GCRs to explain it, though – William]

  37. 37
    William Astley says:

    When will the next ice age begin? Do ice ages begin gradually?

    The current insolation received at the critical latitude of 65N is the same as it was 18kyr ago, during the Last Glacial Maximum, (Laskar 1990; Berger & Loutre 1991). July 4th the earth is at its greatest distance from the sun (156 km) at the aphelion. January 3rd the earth is closest to the sun (146 km) at the perihelion. This orbital configuration is posited to initiate an ice age (Warm winters which increases snow fall and cold summers which enables there to be a gradual build-up snow.)

    Past interglacial periods have lasted no more than 10 thousand years. Is this interglacial different? Why?

    [Response: If what you said about interglaical length was true, then this one would be different in that its lasted more than 10 kyr already – William]

  38. 38

    Re #28 and “Yet some seem to think we’ve stepped outside of history because of a few extra ppm of CO2 in the atmosphere.”

    It’s not “a few extra ppm,” laddie buck. It’s 380 ppmv now compared to 280 before the industrial revolution. My calculator says that’s a 36% increase. I rarely hear 100 ppm described as “a few ppm.”

  39. 39

    Re #29 and “Would someone up on the maths care to comment?”

    Surely. Earth’s present IR flux up from the ground is 390.1 Watts per square meter, corresponding to a temperature of 288.0 K. Add 3.7 so that the flux is 393.8, and the temperature only moves up to 288.7, indicating a temperature sensitivity of only 0.7 K for doubling CO2. Similarly, the flux up at top of atmosphere (TOA) is 239.3 W m^-2, corresponding to 254.9 K. Raise it to 243.0, and the temperature becomes 255.9, for a temperature sensitivity of 1.0 K. Looks like the bad guys won this one.

    Except that they didn’t. Their math is fine, their climatology stinks. The IPCC temperature sensitivity of 3.0 K for doubling CO2 ADDS IN ALL THE KNOWN FEEDBACKS. The figure for CO2 doubling by itself, with no feedbacks, is 1.2 K (Houghton 2004). Thus these guys’ estimate is quite in line with the IPCC estimate.

    The reference to “the seminal work of Sherman Idso” is a joke. I have critiqued some of Idso’s work myself, and it is not only wrong, it is in some places deliberately misleading. For his greenhouse line drawn between Venus and Mars, there were ten figures available from the literature on the bolometric Bond albedo of Mars. Idso chose the darkest of the ten. Thus the Martian effective temperature was way high, so the Martian greenhouse effect came out as way low, surface temperature minus effective.

    Beware of greenhouse denialists bearing gifts. There is frequently a worm or two in the apple they offer you.

  40. 40
    David (Average Joe) says:

    What wonderful insight and thought provoking information this page has to offer. I’m just an average Joe seeking information so I may make informed decisions of my own. I’ve surfed the net a fair bit about our earth’s current climetology but in no way profess to be knowledgable. This site seems to have reached the level of sophistication not found on other web sites.. Here’s what this average Joe has determined through the net.
    1. The earth’s average temperature has risen dramatically since the Industrial Revolution although there has been marked warming and cooling trends during that period. However it has been mostly warming.
    2. Interglacial periods have a track record of ~10K years. This pattern might be, could be, possibly, somewhat or maybe not be influenced by the earth’s orbit, tilt, solar radiation output (maybe not), etc.
    3. Current measurments of CO2 are ~380 ppm which is very much higher than in recent history (~60K years) but no where near some levels experienced in the past 10 million years.
    4. There is several graphs and depictions that GHG emissions lag just slightly behind global warming (graphs I saw of ice sheet data). This then causes more warming which in turn causes more GHG, etc
    5. Man made GHGs are contributing to Global warming. However the earth produces large amounts of GHG regardless of man.

    The question I have is this. If all 6 billion humans ceased to exist tomorrow (call it Kyoto on steroids), what percentage of TOTAL GHG emissions would be eliminated? I seem unable to find the amount of impact that man has on the global climate vs. the impact that good old Mother Nature has. I understand somewhat about Carbon sinks and that currently the rate of total GHG emission does not equal the rate of absorption. There is a plethora of information screaming that man is causing catastrophic climate damage due to GHG emissions with out any comparison to TOTAL GHGs including water vapour. Anyone care to speculate regarding a scenario without man in the equation. Can anyone enlighten me to what was the cause of the massive climate changes the earth experienced pre man. I have no doubt that the earth is warming quickly. What would be the impact if suddenly the earth was devoid of all humans, thus eliminating the human production of GHGs. Thank you for your consideration. I’m sorry for barging in out of the blue and asking this, but it seems I could get the straight goods right here.

    It seems to me that we are pretty much hooped anyways.

    [Response:The human contribution to CO2 is roughly 20 times the natural volcanic flux that maintains the atmosphere’s CO2 content in the absence of industrial activity. –raypierre]

  41. 41
    Grant says:

    Re: #9

    Your conclusions are as mistaken as the “facts” on which they are based. But thanks for giving most of us a good laugh.

    101 weather stations across the U.S. is only a small fraction of the available data; there are over 1200 U.S. stations in the global historical climate network. And *even if* you included all U.S. stations, and came to the same conclusions (which you wouldn’t), the contiguous U.S. is only about 5% of the surface area of the *globe*.

    We’re not your typical global-warming discussion group. *Lots* of us have looked at “actual weather that happened, was recorded and is available for anyone to look and and analyze.” I get the impression that your perspective on this issue is as narrow as the geographic slice on which you base it.

  42. 42
    Hank Roberts says:

    David (Average); lots of sources. Here’s one:
    “Levels of several important greenhouse gases have increased by about 25 percent since large-scale industrialization began around 150 years ago (Figure 1).
    During the past 20 years, about three-quarters of human-made carbon dioxide emissions were from burning fossil fuels.”

  43. 43
    David donovan says:

    Re 40.

    Hank provided some good links. Here is my 2 cents.

    Keep in mind that it is the Total net (sources-sinks) that is important. Natural CO2 sources are larger than the anthro component BUT if you take proper account of the sinks then one finds that the anthro contribution has a BIG effect on the net. Were are emiiting more that the natural sinks can keep up with and until when/if we get serious about carbon sequestering, we are not providing much in the way of sinks. If you earn 10K$ a month and your “natural” level if spending is about the same, you will find that you can go broke or get rich if you change your income or expenses an amount that is small when compared to 10K (but large when compared to your “natural” income-minus-expenses).

    As for the relationship between CO2 and the very important GHG H2O, see Basicly H2O has such a short residence lifetime in the atmosphere it turns out that levels of other longer lived GHS’s end up controling the amount of H2O in the atmosphere (in part because there is a strong relationship between the amount of H2O air can hold and it’s temperature).

  44. 44
    mark schneeweiss says:

    Hiya folks,

    I think Jo Strummer might have meant the Gulf stream shutting down (like in November 2004! TimesOnline, Nature etc)… whilst the rest of world warms, which is why London is drowning:-)

    regards, Mark

    [Response: Not sure why the GS shutting down would drown London – unless some mystical association of oceans comes in. Also not so sure that was one of the ideas floating around in those days – William]

  45. 45
    Gareth says:

    Re: 40 “If all 6 billion humans ceased to exist tomorrow”

    New Scientist‘s October 12 issue had a lead feature on just such a thought experiment, and – miracles – it’s not behind their subscriber-only archive wall. It’s an interesting and thought-provoking read.

    “Carbon dioxide, the biggest worry in today’s world because of its leading role in global warming, will have a more complex fate. Most of the CO2 emitted from burning fossil fuels is eventually absorbed into the ocean. This happens relatively quickly for surface waters – just a few decades – but the ocean depths will take about a thousand years to soak up their full share. Even when that equilibrium has been reached, though, about 15 per cent of the CO2 from burning fossil fuels will remain in the atmosphere, leaving its concentration at about 300 parts per million compared with pre-industrial levels of 280 ppm. “There will be CO2 left in the atmosphere, continuing to influence the climate, more than 1000 years after humans stop emitting it,” says Susan Solomon, an atmospheric chemist with the US National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado. Eventually calcium ions released from sea-bottom sediments will allow the sea to mop up the remaining excess over the next 20, 000 years or so.”

  46. 46
    Olly says:

    As an interested amateur looking at the issues under discussion I see little evidence of other effects caused by man and nature being added to the computer modelsâ?¦
    What about man made cooling effects that offset CO2 and methane production?
    Such as aircraft aerosols emissions, the Hamatan (movement of Sahara dust clouds over Africa â?? sunlight reflector) and large South Asian forest fires are all sunlight reflectors.
    Every time I read about aircraft emissions adding to the CO2 in the atmosphere I never see any reference to the contrails which reflected sunlight.
    Also deforestation due to man made activities does this decrease or increase sunlight absorption?

    The other thing is no one seems to be taking account off is human history in consensus taking.
    A few hundred years ago the scientific consensus was the world was flat and also that witches existed. Looking at it this way makes you wonder what the value of scientific consensus is worth.
    Just my two pennies worthy of comment for what itâ??s worth.

  47. 47

    Re #46 and “A few hundred years ago the scientific consensus was the world was flat and also that witches existed. Looking at it this way makes you wonder what the value of scientific consensus is worth.”

    1. Educated people have known the world is round since about 300 BC, when Eratosthenes measured its circumference. The idea that Columbus proved the world was round is a myth.

    2. There is an analogy between the global warming consensus and the witch trials, but it’s not the analogy you think. Scientists of the day never did believe in witches; the witch craze was a mass movement from the bottom up, a popular consensus. The academics of the day condemned it — the faculty at Tubingen issued a statement that it was “better to cure the soul than to torture and kill the body.” Johann Weyer, now known as “the father of modern psychology,” attributed confessions of witchcraft to mental illness. The analogy to the global warming consensus is obvious. The academics were telling people the popular beliefs were wrong and dangerous. but they got overruled by the politicians.

  48. 48


    A few hundred years ago the people believed that the world was flat, but the scientist knew differently. Why do you think Columbus tried to sail round the world. Why do you think the Queen of Spain financed him?

    Witches were burnt quite recently but not at the insigation of scientists. Many of them were scientists themselves. Galileo only escaped the stake by recanting his science.

  49. 49
    Tim Hughes says:

    re #42

    great, but do you have a source where has anyone actually measured it? (CO2 from fossils should have a different isotope signature from present day CO2, should I would have thought it would be reasonably easy to do.)

    Also, do you have a source for CO2 diffusion? There are very few winds that cross the equator, so does CO2 is the southern hemisphere CO2 level delayed wrt to the northern hemisphere?

  50. 50
    Zeke Hausfather says:

    Re: Olly

    There are many different forcings taken into account beyond simple CO2 emissions. See and for some good examples of the different forcings considered, and their relative magnitudes.