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The IPCC Fourth Assessment SPM

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We’ve had a policy of (mostly) not commenting on the various drafts, misquotes and mistaken readings of the Fourth Assessment report (“AR4” to those in the acronym loop) of the IPCC. Now that the summary for policy makers (or “SPM”) has actually been published though, we can discuss the substance of the report without having to worry that the details will change. This post will only be our first cut at talking about the whole report. We plan on going chapter by chapter, hopefully explaining the key issues and the remaining key uncertainties over the next few months. This report will be referenced repeatedly over the next few years, and so we can take the time to do a reasonable job explaining what’s in it and why.

First of all, given the science that has been done since the Third Assessment Report (“TAR”) of 2001 – much of which has been discussed here – no one should be surprised that AR4 comes to a stronger conclusion. In particular, the report concludes that human influences on climate are ‘very likely’ (> 90% chance) already detectable in observational record; increased from ‘likely’ (> 66% chance) in the TAR. Key results here include the simulations for the 20th Century by the latest state-of-the-art climate models which demonstrate that recent trends cannot be explained without including human-related increases in greenhouse gases, and consistent evidence for ocean heating, sea ice melting, glacier melting and ecosystem shifts. This makes the projections of larger continued changes ‘in the pipeline’ (particularly under “business as usual” scenarios) essentially indisputable.

Given all of the hoopla since the TAR, many of us were curious to see what the new report would have to say about paleoclimate reconstructions of the past 1000 years. Contrarians will no doubt be disappointed here. The conclusions have been significantly strengthened relative to what was in the TAR, something that of course should have been expected given the numerous additional studies that have since been done that all point in the same direction. The conclusion that large-scale recent warmth likely exceeds the range seen in past centuries has been extended from the past 1000 years in the TAR, to the past 1300 years in the current report, and the confidence in this conclusion has been upped from “likely” in the TAR to “very likely” in the current report for the past half millennium. This is just one of the many independent lines of evidence now pointing towards a clear anthropogenic influence on climate, but given all of the others, the paleoclimate reconstructions are now even less the central pillar of evidence for the human influence on climate than they have been incorrectly portrayed to be.

The uncertainties in the science mainly involve the precise nature of the changes to be expected, particularly with respect to sea level rise, El Niño changes and regional hydrological change – drought frequency and snow pack melt, mid-latitude storms, and of course, hurricanes. It can be fun parsing the discussions on these topics (and we expect there will be substantial press comment on them), but that shouldn’t distract from the main and far more solid conclusions above.

The process of finalising the SPM (which is well described here and here) is something that can seem a little odd. Government representatives from all participating nations take the draft summary (as written by the lead authors of the individual chapters) and discuss whether the text truly reflects the underlying science in the main report. The key here is to note that what the lead authors originally came up with is not necessarily the clearest or least ambiguous language, and so the governments (for whom the report is being written) are perfectly entitled to insist that the language be modified so that the conclusions are correctly understood by them and the scientists. It is also key to note that the scientists have to be happy that the final language that is agreed conforms with the underlying science in the technical chapters. The advantage of this process is that everyone involved is absolutely clear what is meant by each sentence. Recall after the National Academies report on surface temperature reconstructions there was much discussion about the definition of ‘plausible’. That kind of thing shouldn’t happen with AR4.

The SPM process also serves a very useful political purpose. Specifically, it allows the governments involved to feel as though they ‘own’ part of the report. This makes it very difficult to later turn around and dismiss it on the basis that it was all written by someone else. This gives the governments a vested interest in making this report as good as it can be (given the uncertainties). There are in fact plenty of safeguards (not least the scientists present) to ensure that the report is not slanted in any one preferred direction. However, the downside is that it can mistakenly appear as if the whole summary is simply up for negotiation. That would be a false conclusion – the negotiations, such as they are, are in fact heavily constrained by the underlying science.

Finally, a few people have asked why the SPM is being released now while the main report is not due to be published for a couple of months. There are a number of reasons – firstly, the Paris meeting has been such a public affair that holding back the SPM until the main report is ready is probably pointless. For the main report itself, it had not yet been proof-read, and there has not yet been enough time to include observational data up until the end of 2006. One final point is that improvements in the clarity of the language from the SPM should be propagated back to the individual chapters in order to remove any superficial ambiguity. The science content will not change.

Had it been up to us, we’d have tried to get everything together so that they could be released at the same time, but maybe that would have been impossible. We note that Arctic Climate Impact Assessment in 2004 also had a similar procedure – which lead to some confusion initially since statements in the summary were not referenced.

How good have previous IPCC reports been at projecting the future? Actually, over the last 16 years (since the first report in 1990), they’ve been remarkably good for CO2 changes, temperature changes but actually underpredicted sea level changes.

When it comes to specific discussions, the two that are going to be mostly in the news are the projections of sea level rise and hurricanes. These issues contain a number of “known unknowns” – things that we know we don’t know. For sea level rise the unknown is how large an effect dynamic shifts in the ice sheets will be. These dynamic changes have already been observed, but are outside the range of what the ice sheet models can deal with (see this previous discussion). That means that their contribution to sea level rise is rather uncertain, but with the uncertainty all on the side of making things worse (see this recent paper for an assessment (Rahmstorf , Science 2007)). The language in the SPM acknowledges that stating

“Dynamical processes related to ice flow not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise. Understanding of these processes is limited and there is no consensus on their magnitude.”

Note that some media have been comparing apples with pears here: they claimed IPCC has reduced its upper sea level limit from 88 to 59 cm, but the former number from the TAR did include this ice dynamics uncertainty, while the latter from the AR4 does not, precisely because this issue is now considered more uncertain and possibly more serious than before.

On the hurricane/tropical strorm issue, the language is quite nuanced, as one might expect from a consensus document. The link between SST and tropical storm intensity is clearly acknowledged, but so is the gap between model projections and analyses of cyclone observations. “The apparent increase in the proportion of very intense storms since 1970 in some regions is much larger than simulated by current models for that period.”

We will address some of these issues and how well we think they did in specific posts over the next few weeks. There’s a lot of stuff here, and even we need time to digest it!

364 Responses to “The IPCC Fourth Assessment SPM”

  1. 251

    [[Global Warming, as we think we know it, doesn’t exist. ]]

    I agree. And the stars are painted on the sky.

  2. 252
    biffvernon says:

    There is a lot of attention being paid to the climate contribution from burning oil by flying, driving etc, but oil is limited. Coal may be a more serious problem.

    IPCC seem to accept CERA figures for future oil production, while these are regarded as nonsense in the Peak Oil community.

    The IPCC claim in their â��Summary of Policy Makersâ�� it will take another 490 [375 to 600] Gt of carbon emissions to give us +2C and 450ppmv yet, according to the latest ASPO newsletter, there is only 162 Gt of carbon remaining in all the available liquids fossil fuels over the coming century. The media seem to have oil in their sights as climate change public enemy number one when that just isn’t the case.

    I’m not saying we don’t face climate disaster – just that oil isn’t half as responsible as people make out.

  3. 253
    John L. McCormick says:

    RE # 242

    Ike, you said

    [In addition, wouldn’t solar forcing be expected to warm the stratosphere, which is actually cooling? ]

    You might look into the very low Antarctic ozone concentrations measured in 2006 and recently. Low concentrations of ozone in the stratosphere would enhance cooling I believe.

    In a later post, I will link several reports on extremely low Antarctic ozone DU readings.

  4. 254
    Eli Rabett says:

    #242 and #243. If you look at the measurements and attribution of cooling in the stratosphere, you see that relatively little of it is due to ozone depletion overall. As a matter of fact if you follow the links to the Stratospheric Ozone Textbook, you will see that there is essentially NO depletion in the tropics (slight exaggeration for point to be made). Therefore, if the entire process is solar driven you would see higher temperatures there, if nowhere else.

    Further, the ozone argument breaks down in the mesosphere and ionosphere. In particular, it would be indicative of solar/cosmic ray influences to know if O2 populations have decreased above the stratosphere due to photolysis, electron/ion chemistry(above~100 km most of the oxygen is found as O atoms).

  5. 255
    Lynn Vincentnathan says:

    RE #106 & 116, I didn’t think there was any evidence we had passed the point of no return….just suggesting that GW-induced mass extinctions had happened in the past (55 mya & 251 mya) & could happen now (esp since our AGW is so much more rapid). If & when there is evidence of this hysteresis upon us, it would be way too late to turn back (I figure scientific certainty about it will be reached AFTER the fact). So, it’s just fine there’s no current evidence. We really don’t want evidence on this, so we need to stop the experiment now.

    RE #163 & 177, the people who post the main articles here are top climate scientists, who publish in peer-reviewed science journals and are employed by top universities and gov research institutes, like NASA. The rest of us are a mixed batch. I’m an anthropologist and criminologist. Perhaps you should know this blog’s purpose is for scientists to explain climate science to laypersons in simple and understandable language. I’ve learn a lot, and I share what I’ve learned with my students, academic community, church, and others. So it is climate science for Mr/Ms Everyperson.

    My main contribution, since I did my thesis on environmental victimology, is to keep pointing out that science is very cautious in its claims, requiring high standards that something is happening before making claims, while (you’d think)policy-makers, victims, environmentalists, moral persons, people living in the world would be more interested in avoiding “false negatives,” avoiding doing nothing to solve a problem when it is actually happening. They’d like high probability a problem is NOT happening, before ceasing to be concerned about it. (Sorry to the regulars here that I sound like a broken record on this.) And I sometimes bring up the human dimension of climate change (as my education is in the human sciences), since humans are causing this and will be affected by it. However, we only know that psychological (cognitive/emotional), social (politics/economics/kinship and so on — the “other people” and social relations factor), and cultural (beliefs, values, ideology, technology) factors play into climate change in various ways, but the human sciences are not that great in predicting as the physical sciences are, hence the wide range of human emission scenarios in the IPCC reports — from “if people are really good and smart” up to “if people are really bad and stupid.”

    But you can take climate science & global warming or leave it if you wish — that’s what I tell my students when I teach evolution, they don’t have to believe it, they only have to learn it to pass the test. So, if you take a course in climate science, I’d suggest learning it for the test, even if your religious or political beliefs disallow you believing in it.

  6. 256
    Ike Solem says:

    Adam, Switching the baseline does matter when you are trying to make a determination of how climate changes relative to a given historical average, as well as when you are comparing th output of a 2001 climate change report and a 2007 climate change report.

    Clearly, using a higher baseline lowers the temperature anomalies, and since anomalies are often discussed as data in place of temperature records, it realy amounts to fudging data to make the observed temperature changes look lower then they actually are relative to the 20th century average.

    If you wanted to look at the variability index, what you’d want to do is compare temperature spikes to the five-year running average.

    For example, look at

    This shows the anomaly record relative to the 1950-1980 period, when global warming had not become evident (although the atmospheric CO2 content was increasing)

    If the IPCC report claims that sea levels were 4-6 m higher in the last interglacial 125,000 years ago, when temperatures were 3-5C higher then they are today, what ‘today’ are they talking about? The ‘today’ they reference in the 2001 report (the 1961-1990 period) or the ‘today’ in the 2007 report, the 1980-1999 period.

    Note that the IPCC report states explicity that 11 of the 12 warmest years on record were in the past 12 years, and that means that they are including the warming trend in their baseline – so what do you think they mean when they say “today”?

    The same argument applies to NOAA, who in their 2005 “State of the Arctic” report discuss ‘warm and cool anomalies’ even though they don’t discuss the fact that they raised the baseline from 1961-1990 to 1971-2000.

  7. 257
    lars says:

    re #248 and @251
    I guess you did not notice it was not me saying it, it was:

    Dr. Tim Ball, Chairman of the Natural Resources Stewardship Project (, is a Victoria-based environmental consultant and former climatology professor at the University of Winnipeg. He can be reached at

    As for so called scientific consensus, there have been many and completely wrong, remember the flat earth people, remember the earth as the center of the universe, etc etc etc….

  8. 258
    Ike Solem says:

    Lynne, you say – “But you can take climate science & global warming or leave it if you wish — that’s what I tell my students when I teach evolution, they don’t have to believe it, they only have to learn it to pass the test”

    Ouch! I winced when I read that – pardon me, but that is the worst approach to teaching science that exists – rote memorization and regurgitation. Science is based fundamentally on reliable and exchangeable information – Richard Feynman, a great scientist and a great teacher (a truly rare combination) explained science as something you explain to someone else on the other side of the world through a telephone – i.e. if you set up the experiment I describe, then you should get this result; pass a light beam through a glass prism, you should see a rainbow of colors – it’s all about independent verification, not about rote memorization of some text.

    Really, there is no worse way of teaching science then the method you just described!

  9. 259
    Dan says:

    rE: 257. Oh please. There was never a scientific consensus about the earth being flat (I believe this has been discussed at length here at RC). That is a tired, very old red herring that is constantly repeated with no evidence to support it. Simply repeating what someone may have told you is not a fact and spreading disinformation. For example, Columbus did not sail off from Spain thinking he would fall off the face of the earth. Maps of the earth showing it was round existed.

    Please learn about the meaning of scientific consensus, specifically how a consensus is attained and the methods that are followed. To make any assumptions without a fundamental understanding of what is involved is disingenuous. And to disavow literally thousands of scientists compared to a personal belief that does not stand up to scientific, peer review is simply wrong.

  10. 260
    Ike Solem says:

    Charles, first if we look at the IPCC report (which is clearly consevative in terms of the science), the solar and volcanic forcings are indeed included. Look at figure SPM-4, where the blue band represents the 5-95% confidence interval for runs of 19 models using only solar and volcanic forcings – your question seems to be, what accounts for the pre-WWII excursion of the actual temperatures above the ‘natural forcings’ – well, people were buring a lot of fossil fuels in those days as well – there’s no need to call on an additional ‘natural forcing’ – humans are ‘natural’, aren’t we?

    So, why does Solanki’s reconstruction, based on a single Greenland ice core, find such a widespread acceptance among contrarians? They say that the ‘period of high solar activity in the last 60 years is unique during the past 1,150 years. However, the solar maximum peaked back in 2001 – see NASA scientists who monitor the Sun say that our star’s awesome magnetic field is flipping – a sure sign that solar maximum is here. Feb 2001

    So, what effect does this have on climate? The notion that cosmic ray fluxes causes changes in cloudiness thereby controlling climate has been disposed of. So, what is the variation in solar irradiance? There is only 25 years or so of satellite data on this issue, meaning that there is plenty of wiggle room for those who wish to blame global warming on something other than human use of fossil fuels. One must rely on the paleoclimate record.

    There are two approaches: 14C in tree rings, and 10Be in ice cores, both of which are produced by cosmic rays striking the top of the atmosphere. The 14C tree ring record has also allowed researchers to show that the accumulation of carbon dioxide in the atmosphere is due to burning of fossil fuels (since million-year old fossil fuels are lacking in 14C). The 14C record does not agree with the single ice core record that Solanki and the contrarians rely on for their claims of a dominant solar influence on climate, and neither do other 10Be records.

    Thus, if the 14C and 10Be records all agreed with one another, and with the neutron data, then they might have an argument – but they don’t. In addition, since we are now approaching a minimum of the 11-year sunspot cycle, the climate should be cooling if global warming was due to solar forcing (see above link) – but instead we see a continued warming trend with new record temps being set every year.

    However, the public relations departments have picked up on this argument, and are widely promoting it; see for example:Talking Point#40: Sun is Real Culprit in Global Warming, 1998 According to that, we’re supposed to be entering a period of ‘global cooling’…

  11. 261
    Charles Muller says:

    #254 Eli

    Thanks for the link and the textbook. I don’t understand where the first graphic come from. In fact, there is some ozone depletion in low-latitudes and mid-latitudes, less pronounced than over South Pole, not located at the same geopential for the maximal amplitude (see a recent assessment from Brunner et al. 2006 thereafter).

    Atmos. Chem. Phys., 6, 4985-5008, 2006
    Variability and trends in total and vertically resolved stratospheric ozone based on the CATO ozone data set
    D. Brunner1,*, J. Staehelin1, J. A. Maeder1, I. Wohltmann2, and G. E. Bodeker3
    PDF available at

    Have a look at channel TLS (1979 – 2006) on RSS (maps thereafter) : there’s a quite heterogene distribution of cooling and warming zones for lower stratosphere, but mid- and high- latitudes southward have clearly the max. cooling.
    On the same page, the graph under the TLS map : no clear trend between 1995 and 2006, cooling was much more pronounced between 1980 and 1995 (before Montreal protocole first effects, maybe, but just an hypothesis).

    I’m still skeptic about GHGs as a main driver of cooling stratosphere. Anyway, as I explained, these recent trends (past 20 yrs) are not really interesting, so far everybody agree there is few if any solar trends between cycle 21 and 23. I question if yes or no 19-22 cycles (approx.1950-90) are the most active of the past 150 years, if solar signal may be delayed by oceanic thermal inertia (so far solar warms the first 100 meters of oceans, 70% of globe surface), if our current undestanding (low) of solar variability and solar-climate connexion are sufficient for any “very likely” conclusion, etc.

  12. 262
    Lynn Vincentnathan says:

    #258, very much agreed, Ike. I do that just to avoid endless, disruptive debate in class, since I’m here in the Bible belt & evolution is a dirty word (like communism). I just had a class last week in which I told them I was a religious person who believed in evolution, that the 2 are not incompatible, that in fact evolution and science in general even strengthen my religious beliefs. And that led to an endless debate, wasting half a class period. I have to think about the other students, who want to learn.

    Same with climate change contrarians, some are so set in their disbelief, that at some point it becomes a waste of time trying to convince them (in fact, that may be one of their ploys — getting people to waste their time, so as not to do anything about GW).

    RE #198, Martin, I posted my #255 comment before reading your #198 comment (I wrote it yesterday, then posted today). Yes, a shift to a society reducing its GHGs will open up a lot of business opportunities, and if you read NATURAL CAPITALISM, you will get a sense of how the economy can even improve in doing so (see: ). As for a social science scenario, I look forward to a “revitalization (or social) movement” in which people try to construct a more satifying culture and society. These happen rather quickly (like an ice sheet breaking off), not like cultural evolution. So we could wake up any day now, and nearly everyone will be tauting solutions to GW. For now it’s “in my dreams!”

  13. 263
    lars says:

    Re #259

    Ok Einstien…. are you a big bang universe or steady state universe?

    are you a Closed universe, Open universe or Flat universe?

    a theory is only a theory, until it can be proved…..

    BTW Einstien was a steady state universe guy….. does that make him stupid?

  14. 264

    [[As for so called scientific consensus, there have been many and completely wrong, remember the flat earth people, remember the earth as the center of the universe, etc etc etc…. ]]

    Who were “the flat earth people,” exactly? Aside from Cosmas Indicopleustes, that is.

  15. 265

    [[Lynne, you say – “But you can take climate science & global warming or leave it if you wish — that’s what I tell my students when I teach evolution, they don’t have to believe it, they only have to learn it to pass the test”

    Ouch! I winced when I read that – pardon me, but that is the worst approach to teaching science that exists – rote memorization and regurgitation. Science is based fundamentally on reliable and exchangeable information – Richard Feynman, a great scientist and a great teacher (a truly rare combination) explained science as something you explain to someone else on the other side of the world through a telephone – i.e. if you set up the experiment I describe, then you should get this result; pass a light beam through a glass prism, you should see a rainbow of colors – it’s all about independent verification, not about rote memorization of some text.

    Really, there is no worse way of teaching science then the method you just described! ]]

    I don’t think she was talking about rote memorization, or not only that. Nothing she said ruled out helping students to understand the concepts involved.

  16. 266

    [[Ok Einstien…. are you a big bang universe or steady state universe?
    are you a Closed universe, Open universe or Flat universe?
    a theory is only a theory, until it can be proved…..
    BTW Einstien was a steady state universe guy….. does that make him stupid? ]]

    No. Einstein died in 1956. Although there was already some evidence by then that the ratios of Seyfert and N-galaxies fell off with distance, which shouldn’t happen according to Steady-State, it would be nine years before Penzias and Wilson discovered the cosmic microwave background, thus moving the Big Bang into consensus and pretty much killing Steady-State.

  17. 267
    Dan says:

    re: 263. “a theory is only a theory, until it can be proved…..” Ah yes, the tired and very dated attack on the scientific method now (we do live in the 21st century now, not the Middle Ages). Look, “proof” is a mathematical property. Until you learn that fundamental concept and how the scientific method works (it was used to develop the basics for computers such as the one you are typing on), your conversation is dead. See

    Einstein is the perfect example of someone who followed the scientific method. He had a hypothesis, he gathered data, conducted experiments, published them for peer-review, and made new hypotheses based on the information he and others found for further research. If you are going to reference someone, be sure he supports your point.

  18. 268
    Hank Roberts says:

    21st Century Science, Medieval Hot Air
    It’s a puzzle which to choose, isn’t it?

  19. 269
    James says:

    Re #257: “As for so called scientific consensus…remember the earth as the center of the universe…”

    In fact, though, there was never a _scientific_ consensus on geocentrism. There was a cultural and religious one, within which early protoscientists were constrained to work. As soon as scientists like Copernicus started actually looking at the data, that consensus fell apart.

  20. 270
    lars says:

    Re 266

    The idea of a static universe is one which demands that space is not expanding nor contracting but rather is dynamically stable. Albert Einstein proposed such a model as his preferred cosmology by adding a cosmological constant to his equations of general relativity to counteract the dynamical effects of gravity which in a universe of matter would cause the universe to collapse. After the discovery by Edwin Hubble that there was a relationship between redshift and distance, Einstein declared this formulation to be his “biggest blunder”.

    Hubble’s law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. The law was first formulated by Edwin Hubble and Milton Humason in 1929[1] after nearly a decade of observations. It is considered the first observational basis for the expanding space paradigm and today serves as one of the most often cited pieces of evidence in support of the Big Bang.

    Re #367

    your link goes to Page Not Found….. good one……..

  21. 271
    tamino says:

    Re: #269

    As far as my knowledge of the history of science goes, there was indeed a truly scientific concensus on geocentricism, stretching from the days of ancient Greek science until its overthrow by Copernicus, Galileo, Kepler, and eventually Newton.

    Very few would dispute the point, that consensus is not proof. But it is the best we’ve got. The stronger the consensus, the more likely it is to be correct, and the concensus on global warming is as strong as you’ll find. Furthermore, the consensus on global warming is not an old, tired consensus being attacked by new theory. It is itself the “new kid on the block” that has overthrown the old, tired, and mistaken consensus that the human race is too puny to cause global climate change.

  22. 272

    Clarification please:

    You write “Note that some media have been comparing apples with pears here: they claimed IPCC has reduced its upper sea level limit from 88 to 59 cm, but the former number from the TAR did include this ice dynamics uncertainty, while the latter from the AR4 does not”

    I look at the TAR and see this explanation:

    “The region in light shading shows the range of all AOGCMs for all 35 scenarios. The region delimited by the outermost lines shows the range of all AOGCMs and scenarios including uncertainty in land-ice changes, permafrost changes and sediment deposition. Note that this range does not allow for uncertainty relating to ice-dynamical changes in the West Antarctic ice sheet.”

    It read as it the TAR also did not consider ice dynamics uncertainty. Can you clarify this please?


    [Response: The TAR range included mass-balance estimates for the Greenland and Antarctic ice sheets (though did not include dynamical changes – i.e. changes due to changes in ice streams, calving, grounding line movement, etc which were then thought to be small). Recent observations point to the vital importance of such terms in assessing the net mass balance, thus since they are highly uncertain, it was thought more prudent to not include the mass-balance terms this time around. Our statement above should probably state that “the former number from the TAR did include some ice-sheet mass balance uncertainty, while the latter from the AR4 does not”. -gavin]

  23. 273
    Lance Armstrong says:

    Has anyone else noticed that the SPM available at the link provided has gone from 21 pages down to 18? I haven’t sorted out what exactly is missing, but the scenario descriptions are now on the last page, and they used to be back on page 14. Has there been a revision? Shouldn’t that be mentioned somewhere?

  24. 274
    Dan says:

    re: 270 “your link goes to Page Not Found….. good one……..”

    Gee, a very simple inspection of the URL address would tell you to leave off the period at the end, sport. As in
    It is not rocket science to figure that one out.

    And please do not forget to read up on the meaning of the “scientific method” and what the concept of “proof” is all about.

  25. 275
    Vicky says:

    Re:#149 and 160.

    Asa, if you’re after an economic interpretation of the costs of climate change, see Sir Nicholas Stern’s review on it, published in the UK last year. It is an excellent report, broken into chapters on things like mitigation, adaptation, modelling etc. Whilst I’m not sure if it covers fossil fuels directly, it is implied, and well worth a look.

    The one drawback is that as it was published in 2006, it draws projections from the Third Assessment, but you, as an economic-based person, could look at the difference in projections from the AR4 and roughly tell which direction the costs go.

    Hope that helps.

  26. 276
    lars says:


    Among other facets shared by the various fields of inquiry is the conviction that the process must be objective so that the scientist does not bias the interpretation of the results or change the results outright. Another basic expectation is that of making complete documentation of data and methodology available for careful scrutiny by other scientists and researchers, thereby allowing other researchers the opportunity to verify results by attempted reproduction of them. This also allows statistical measures of the reliability of the results to be established. The scientific method also may involve attempts, if possible and appropriate, to achieve control over the factors involved in the area of inquiry, which may in turn be manipulated to test new hypotheses in order to gain further knowledge.

  27. 277
    Dan says:

    re: 276. That last sentence is not an acccurate description of the scientific method whatsoever. Especially the crock about “achieving control over the factors”…”which may in turn be manipulated…” Sorry, that is simply not the way it is done. New hypotheses are tested but it is not due to “manipulation” over the factors involved. Manipulation removes objectivity and does not jive with the method.

  28. 278
    Dan says:

    re: 277. I neglected to add that yes, I know that came from Wikipedia’s supposed definition of the scientific method. Such as it is.

  29. 279
    Mark Hadfield says:

    Re 272: Roger, I see you have an article on this subject on your blog:

    I’m not sure that you’ve grasped the distinction between mass balance uncertainties and ice-sheet dynamics uncertainties, but, hey, what do I know?

    Perhaps Gavin or Stefan could comment.

  30. 280
    Aaron Custance BSc (UK) says:

    Doesn’t an increase in atmospheric, anthropogenic CO2 mean a decrease in atmospheric O2, and a decrease in atmospheric volume(before considering expansion due to warming)?

    I recall the classroom experiment that demonstrates the air volume reduction commensurate with the burning of carbon (a candle) in a closed system (bell jar inverted in water). While consuming oxygen and releasing CO2 and H20, the floating candle rose up in the jar some 20% (by memory) before extinguishing, even with the system temperature having risen (unmeasured, but likely several degrees C) .

    Assuming botanical sequestration (and photosynthetic O2) deals with a quarter of our global 9Bn T output of CO2, that still leaves the other three-quarters of the volume reduction effect. With the Earth’s photosynthetic capacity diminished(rainforest destruction, desertification, forest fires), shouldn’t we be talking about O2 levels and atmospheric volume (and including them in our climate models)?

    [Response: Try the math yourself. Take a million molecules of air. How many molecules of O2 do you have? Now how many of those do you need to use to double CO2 (i.e. add about 280 molecules of CO2)? So how much does that change the fraction of O2 in the air? It’s small, but as a diagnostic of fossil fuel burning it’s interesting. However, we’re not going to run out of air to breath and the associated surface pressure changes (extra credit: does surface pressure go up or down in this process?) are not going to change the circulation to any significant degree. In fact, the main influence of global warming on surface pressure comes from the additional water vapor in the atmosphere. Still a small effect, but bigger than the CO2 effect. –raypierre]

  31. 281
    Mark Hadfield says:

    What? Scientists don’t (shouldn’t) manipulate controlling factors to test hypotheses? Damn, so that’s what I’ve been doing wrong!

  32. 282
    Mark Hadfield says:

    Re 280: the bell jar experiment has always puzzled me. I mean, assuming the fuel is a solid hydrocarbon, CnH2n+2 or similar, C + O2 -> CO2 gives no reduction in gas volume and 4H + O2 -> 2H20 gives an increase. Does the reduction occur when the H20 condenses and/or the CO2 dissolves?

  33. 283
    S. Molnar says:

    Re 272 and 279: I am growing more confused on this issue. My assumption from reading the SPM was that the only thing left out was a possible change in ice dynamics. If I read Gavin correctly, he’s telling me that they also left out non-dynamic ice mass balance uncertainties, but I don’t know quite how to interpret that. The ice dynamics are explicitly assumed to exhibit a constant flow rate based on observations from the recent past, but what about melting? Same as before? Increasing linearly with temperature? And what about snowfall in the interior? I don’t know if I’m just being muddleheaded or if there’s a technical use of some terminology that I’m missing, but a more complete explanation for dummies would be much appreciated.

  34. 284
    mark s says:

    Hiya all,

    I think the FAR has had quite alot of success, judging by the traffic RC is getting.

    Talk about rattling the contrarian/confusniks cage. Good grief! :-)


  35. 285
    Ike Solem says:

    RE#262, 265
    Lynn & Barton: Well, I suppose I meant that saying “you don’t have to believe it, you just have to learn it in order to pass the test” gives students a poor idea of what science is about – if you don’t believe it, you should ask questions about it. I imagine there are very few people who actually think that a divine being placed fossils in the ground to test the faith of the true believers, after all.

    For example, take this baseline issue. If your students asked, “what do they mean by the temperature is increasing? Increasing from what? It’s warm in the summer, and cold in the winter – what do they mean when they say it is going to get ~3C warmer as the CO2 level doubles from it pre-industrial level? That’s not very much!”, how would you respond? (That seems like a reasonable question for a student to ask.)

    Well, you’d first have to explain what was meant by the ‘normal climate’ – and you could explain that scientists picked a certain time period as a baseline to compare changes to, and that they all use the same baseline so that they can compare their results to one another. You could also explain that the 3C is a global average, and and that the poles will get much warmer than their baseline temp (10C?), and the equator would not warm as much.

    You could also discuss how temperature and heat relate to one another, and show them that it is a truly massive amount of heat (a good example would be in terms of say, 1 megaton nuclear weapons – how many 1 megaton nukes would you have to set off in the atmosphere to raise the average temperature of the planet by 2 degrees C – anyone want to take a stab at that?)

    Then your students ask you, “well, all these reports use different baselines! 1950-1980, 1961-1990, 1971-2000, 1980-1999 – if they say the ‘equilibrium climate sensitivity’ is 3C, that’s compared to what?” How do you respond to that?

  36. 286
    Hank Roberts says:

    > increase in CO2 …. decrease in O2?

    This is a misunderstanding that I think goes in skeptical circles back to a misapprehension by an economist(?) named Curtin, which started with his asking

    “… what happened to the 100 ppm of the atmosphere displaced by CO2 since 1750?” by: Tim Curtin | June 19, 2006 08:37 AM ”

    The issue was rather well thrashed out. It’s a rowdier forum than this one. Basic confusion was that measurement in ‘parts per million’ does not mean the total number of molecules has to be exactly one million. it’s not a zero sum game because photosynthesis is so good at adding oxygen from water so the level of oxygen in the air overall doesn’t go down as carbon is burned.

  37. 287
    Mark Hadfield says:

    RE 283: I thought the SPM *was* a summary for dummies … oops, policymakers.

    Seriously, if you’re a policymaker who is not hung up on the question of whether AR4 differs from TAR (and why would you be?) the AR4 message is not all that confusing: there’s some stuff we think we understand and here are the results and there’s some other complicated stuff that we’re not at all sure about and we’ll get back to you later on that. Simple!

    Oh, you want to *understand*? Ah, well that’s a bit harder…

  38. 288
    Eli Rabett says:

    #280 Ralph Keeling has done some beautiful work on O/N changes in the atmosphere and O isotope ratios. The effect of combustion is observable.

  39. 289
    tamino says:

    Re: #280, #282

    There’s an excellent paper on the bell-jar experiment in the journal of chemical education here. Fascinating reading.

    BTW Raypierre, my guess is that the surface air pressure goes up, because replacing a single O2 with a single CO2 doesn’t change the number of gas molecules, but does make the atmosphere heavier. Atmospheric pressure is, after all, the weight of all that air over our heads. Do I get the extra credit?

    [Response: Right, you got it. It’s the hydrostatic law in action. You’re just moving carbon from formerly buried fossil fuels into the air. –raypierre]

  40. 290
    Steve Latham says:

    Along these lines (#289), I have a question that is perhaps naive: As the sky falls (a previous post on RC) does the amount of the Sun’s radiation that is refracted (or whatever) in the atmosphere toward the Earth’s surface change?

  41. 291
    Urs Neu says:

    Re 256,285
    Ike, maybe you missed my comment to the baseline problem in 247.

  42. 292

    [[You could also discuss how temperature and heat relate to one another, and show them that it is a truly massive amount of heat (a good example would be in terms of say, 1 megaton nuclear weapons – how many 1 megaton nukes would you have to set off in the atmosphere to raise the average temperature of the planet by 2 degrees C – anyone want to take a stab at that?)

    Then your students ask you, “well, all these reports use different baselines! 1950-1980, 1961-1990, 1971-2000, 1980-1999 – if they say the ‘equilibrium climate sensitivity’ is 3C, that’s compared to what?” How do you respond to that? ]]

    1. To raise the temperature of the atmosphere 3 K, I calculate as follows. The mass of the atmosphere is about 5.136 x 10^18 kilograms. The specific heat of average wet air is about 1,010 Joules per Kelvin per kilogram. So you need 1.556 x 10^22 Joules.

    A kilogram of TNT releases about 4.18 million Joules when detonated. A ton is 4.18 billion, a megaton is
    4.18 x 10^15 J. Therefore, you would need to detonate 3.72 million 1-MT bombs to heat the atmosphere that much. (Actually, some of the energy goes into blast, large-scale air motions, and not directly to temperature — so you’d need even more.)

    2. The equilibrium climate sensitivity being 3 K means, if you double the amount of carbon dioxide in the air, then, taking into account all the known climate feedbacks, the surface temperature of the Earth would rise by about 3 K.

  43. 293
    Adam says:

    Re 256:

    There may or may not be some in NOAA (or above) who are quite happy for confusion to set in, but NOAA is not alone in this sort of thing. See the MetO & NOAA websites:

    You’re right that NOAA’s a bit ahead of the game, as the WMO still uses 61-90 (I was wrong earlier), and there is no mandate to update to a newer one until 2021 (I think). However some countries are already seeing the 61-90 baseline as a bit meaningless.

    The IPCC needs to be clear what baselines it’s using, and so does any other use of anomalies. See post 247 for more.

    If you use the 61-90 baseline then you will have less -ve anomalies and more +ve and if you use the 71-00 baseline you’ll have more -ve and less +ve. “Now” will always mean the latest baseline (as it should – in twenty years time why should “Now” refer to the 1960s?).

    This can make +ve anomalies to pre-AGW pattern emergence look smaller to the casual viewer, which is (possibly) why the GISS (and I guess the CRU) keep their baseline constant. If however you’re giving a forecast or a meteorological summary, you would say that “above average” is above what the population see as currently average.

    The “State of the Arctic” report may well have needed to make a bigger point of the new baseline, but if it means that a year in the ’60s was average is now below average, it would still show past years to have more -ve anomalies than before. I don’t know though, as I’ve not read it.

    Re 285

    “Then your students ask you, “well, all these reports use different baselines! 1950-1980, 1961-1990, 1971-2000, 1980-1999 – if they say the ‘equilibrium climate sensitivity’ is 3C, that’s compared to what?” How do you respond to that?”

    Compared to the average temperature at the previous equilibrium (before you started adding CO2). In this case, pre-industrial times. The value will be the same, but the anomaly will change (eg “from 1 less than now to another 2 on from now” or “from 0.5 less than the 1960s to another 2.5 on from the 1960s” – I’ve made the figures up BTW).

  44. 294
    Lynn Vincentnathan says:

    RE #284, well, actually, Ike, while I allow students to stick with their religious beliefs re evolution (which some feel is an extreme threat to all they hold dear in life), I do not allow anyone their own beliefs re AGW. I don’t really teach this topic (and I barely touch on evolution, since I’m a cultural, not physical, anthropologist), but I do occasionally mention AGW, and make it clear the science is in on it.

    For the most part students don’t have the foggiest of what I’m talking about, so it’s all new to them. However, I did get 2 grad students last semester who debated me bitterly, stating that AGW was not supported by science. One even said her father was an eminant greenhouse gas scientist in ?Utah?, who totally disclaimed AGW. But I held to my guns and said they were wrong, and suggested they read science journal articles on it. To which the other one said she gets Science delivered to her home, and their articles disprove GW. I only have time to read an abstract now and then, so based on that I again said she’s wrong. To avoid wasting more time I had to change the subject back to the day’s topic.

    I don’t have the background or ability to argue about GW much scientifically, except the basics. Thank goodness for this site. I just refer people to it, especially if the argument goes over my head.

  45. 295
    Lynn Vincentnathan says:

    And, of course, I refer them to the IPCC, which I’ve been doing for years, even before RC.

  46. 296

    [[One even said her father was an eminant greenhouse gas scientist in ?Utah?, who totally disclaimed AGW.]]

    It sounds like she was snowing you. What the heck is a “greenhouse gas scientist?” A chemist? If so, that hardly qualifies him on climatology. A physicist specializing in radiative transfer? Then he ought to know better.

    I have the strong suspicion her father is some kind of engineer, and she thinks he’s a scientist.

  47. 297
    A. ROSARIO says:

    If compliance targets for anthropomorphic CO2 emissions still call for CO2 emmissions at or near current levels. Even with cut backs in the developed world, How are we going to even have a chance of impacting on CO2 levels while at the same time have developing economies in Asia, Latin America & Africa increasing their carbopn footprints without strageties that sequester massive amounts of Carbon. Has additional research has been done with Iron-Catalyzed Plankton Restoration? What I have seen so far looks promising.

  48. 298
    Jeremy Kenyon says:

    So much excellent work is being done by so many people around the world, but it seems to me that communicating the results to policy makers and the public is a dismal failure, leaving it to the press, TV and film makers to do their best to interpret things.

    The SPM is a Summary for Policymakers. I would hazard a guess that less than 1 in 100 policymakers will understand it, so they will all have it interpreted by their own scientists, thus introducing a totally unnecessary layer of confusion. It is not at all surprising that people pick up on the 88cm dropping to 59cm – its tough reading to do more than glance at a few tables and pick the highlight.

    In business, a report is targeted at its audience – SPM seems to be more of a summary for climate scientists of yesterdays news (given that it misses out the recent developments, and gives an artificially good picture).

    It also refers to 6 scenarios, which I know are well understood by climate scientists, but policy makers don’t have that background, and even if they did, a Summary should describe them in a clear fashion – eg reduce emissions to 1990 levels by 2020 and population stays under x and air travel doesn’t proliferate etc. The table stuck at the end of the SPM is just not going to make sense to our politicians – it needs to be stated near the start of the report, in terms PMs will understand.

    The whole point of the work being done around the world is to help policy makers make the right choices. The SPM should clearly show a range of scenarios, and what is the likely outcome from each one, albeit with caveats.

    The summary might be better presented as a small introduction, then a section on each scenario, with its resulting CO2, temperature and sea-level outcome. Then, because there is too much slack between CO2 and temperature/sea-level estimates, just describe the resulting situations for a set of temperature/sea-level combinations, noting which scenarios are likely to result in that situation. That would also help deal with the contrarians who say that it is not CO2 or not human changes, but that it is natural. The consequences are there no matter what the cause.

    The SPM fails to mention just about any real world consequences of the various scenarios. A good report should include examples that will be understood by the target audience. Rather than only say vague things like “Increased incidence of extreme high sea level”, give examples for each scenario, such as Thames Barrier needing renewing by x date, Bangladesh population needing relocating by y or whatever it is.

    The report needs to push back a lot of the superfluous details and actually tell policy makers about the consequences of the detailed report, in understandable terms, for each of the scenarios. So far, it is programs such as the David Attenborough ones and Al Gore’s movie that have best explained it in ways policy makers will understand, but they are interpretations only, and both are short on what the background scenario was. I won’t knock either, but I think the IPCC should be setting the background for those sorts of things, rather than them being left to the tv and film makers and their scientific advisers.

    Table SPM2 is typical of the meaningless data in the SPM – it doesn’t even say which scenario it refers to – as if all the scenarios are equivalent – the whole point of having multiple scenarios is to show how the choices we make will affect the outcome.

    Also, while I do care about things like Polar Bears starving and know that things such as the arctic getting warmer has huge knock-on effects for us, I am not sure that it carries much weight with policy makers. They care about how they are going to feed their populations, whether they are going to have to spend trillions on sea defences and relocating people, whether thousands of people are going to die every summer in heat waves. The SPM should have less comment about obscure happenings far away from anyone, and more about the consequences of those happenings on human populations around the world.

    Also, we should stop assuming that all badness happens at 2100 and then stops getting worse – it doesn’t, but there are very few indications of that in the SPM. There is talk of huge inertia in the system, but the real world explanation for scenario A1F1 should say that sea levels will rise by up to 59cm by 2100, causing x, y and z, followed by another xxcm rise by 2200, causing p, q and r. Similarly for other consequences such as ocean acidification and drought.

    Unless the IPCC report writers want the same set of folks (journalists and government scientific advisers) to re-interpret the report for policy makers, the SPM needs renaming to SCS (Summary for Climate Scientists) and a real SPM writing that clearly shows how the choices we make about emissions reductions will affect the outcome in 50, 100 and 200 years.

  49. 299
    SecularAnimist says:

    It seems to me that much of the discussion following the release of the Fourth Assessment SPM has been about the prospects for sea level rise. However, as far as I know, even in the worst-case scenarios sea level rise would be expected to take many decades at least. Clearly that is a huge challenge given the major cities all over the world that would be affected, but sea level rise is not something that is going to be a sudden catastrophe, as in the global warming fantasy movie The Day After Tomorrow.

    However, there is something that it seems to me could be a major sudden catastrophe: drought. Drought is the sort of “extreme weather event” that global warming might be expected to lead to, and unlike sea level rise, it could occur suddenly and without any advance warning.

    Consider the drought that is currently affecting Australia. Now, imagine that a similarly intense, extreme, and prolonged (i.e. multi-year) drought hits the North American grain producing regions, and that perhaps simultaneously, other major grain producing regions of the world are also afflicted by drought. This could lead to mass starvation — the deaths of tens or hundreds of millions of people from starvation — within only a few years.

    What does the science have to say about the possibility of such an event?

  50. 300
    SecularAnimist says:

    Lynn Vincentnathan wrote: “… I allow students to stick with their religious beliefs re evolution (which some feel is an extreme threat to all they hold dear in life) …”

    Even more than that, for many people whose religious beliefs deny evolution, evolution is an extreme threat to their hopes of an afterlife. Thus evolution denies their hopes for immortality, and forces them to confront their own impermanence.