Ian Plimer on the Science Show

(9/9/09 – Note that this is a post from 2007 about a radio interview, well before the publication of the book Heaven & Earth, though many issues dealt with here are still being raised in more recent interviews, so you may find it to still be of interest, but for up to date info you can see this update)

This week Ian Plimer, Professor of Mining Geology at the University of Adelaide was one of the guests on the ABC’s Science Show to talk about his scepticism of Anthropogenic Global Warming (AGW). There is a transcript available here. There was some response to his points later in the show, but I have quite a bit more to add below the fold.


Prof. Plimer begins by pointing out that the Earth has experienced huge changes in climate in the past. No doubt he his very well qualified to make this claim, and I would be very surprised if any of the climate scientists who support AGW theory would disagree with it.
Plimer continues

And so when we look at the history of climate change and then we look at what people are claiming today, it really is very minor, and it’s very minor compared with what we see in nature. So I’m firstly sceptical that this is due to human activity …

So he is saying that the historical climate makes him sceptical that the currently observed changes are due to humans. For a start he is comparing changes that have taken place on geological time scales with something that has taken place in a hundred years or so. Saying that changes on a small time scale are small compared with changes that happened over hundreds of thousands of years isn’t saying an awful lot.

What’s more, the fact that changes have taken place in the past does not rule out human influence now. This is equivalent to acquitting a murder suspect because they point out that people have died from natural causes in the past. Of course, if the basis of the trial had been that someone was found dead and therefore they had been murdered then this argument might have some relevance – and this is exactly the sort of straw man AGW theory that Plimer’s argument knocks down. If you believe that AGW amounts to something like “The climate is changing. Therefore humans are responsible.” then you’ll find this argument very convincing. But what we have is a very strong theoretical basis (the chemical properties of carbon dioxide), together with measurements of the changes to the atmosphere due to our activities (known by analysis of carbon isotopes, or simply by a knowledge of our fossil fuel use), sophisticated computer models for predicting the affects of this and observations which confirm the theory. This is just a brief overview, but my purpose here is not to go over all of the evidence for AGW, rather just to explain why I am not satisfied by Prof Plimer’s criticisms of it. If you want all the details they are in the IPCC AR4 report. Roughly speaking,in the murder trial analogy we have a motive, a murder weapon, a plausible reconstruction of the events and witnesses whose testimony supports this. Perhaps there’s no confession, and maybe it turns out that the witnesses are unreliable, or there’s an even more likely suspect – these would be grounds for doubting guilt, but the fact that the same result (death) has had other causes in the past would not.
We’ll move on to his next point.

secondly I think those who are claiming that humans actually change climate need to explain various changes which we see in our lifetime in history and in archaeology. We need an explanation. Why did the temperatures decrease between 1940 and 1976, at a time when carbon dioxide was increasing? Why did we have the medieval climate optimum, the Roman climate optimum, the Minoan climate optimum? Why have we got these massive cycles which we see in the Sun and we can tie that in to the new isotopes that solar activity generates, and we tie that in over geological time, over archaeology and over history, and we can see that there is a strong correlation. Now, correlations don’t mean very much at all in science…

He poses these questions as if they present major problems to AGW. Now perhaps he is aware of the explanations for all of these things and isn’t satisfied with them (to be fair, there was limited time available in the interview), but to my mind, these are presented as questions that AGW theory does not have explanations for. Actually the explanations exist, and are well known. The 1940-76 decrease is explained by the effect of particles from industrial pollution reflecting sunlight back into space (which contrasts with C02 which lets direct sunlight through, but traps radiation emitted back from the earth’s surface). This effect declined as stricter pollution controls were introduced. Sure, C02 was increasing as well but no-one claims that C02 is the sole influence on climate, there are always a number of competing influences, but post-1976 C02 has really taken over as the biggest. Read more about this here.

Next there is the question of climate in medieval, Roman and Minoan times. Firstly, we once again have the situation that the existence of warming then does not disprove AGW now. As it turns out the best estimates are that those times were not as warm as it is now anyway, and did not experience global change at the pace that we are now observing. For a start, remember that all claims about climate in those times are based on reconstructions of some sort. There were no thermometers to record the temperature. There may be historical records, evidence of thriving agriculture, evidence of the presence of certain species, and so on. This archaeological evidence tells us about local rather than global climate. Now paleoclimatologists have been able to use many more proxies, from a wider variety of locations, to get a global picture and are satisfied that these historical instances of warmer temperatures do not compare directly with what is happening today. There is an explanation in more depth with additional links here.

I’m afraid I’m not entirely sure what Prof. Plimer is referring to in terms of solar cycles, since he didn’t have a chance to elaborate. At first I thought perhaps the 11 year sun spot cycle, but the mention of geological timescales suggests rather the Milankovitch cycles. If this is what he means, then I don’t believe it presents any problem for AGW since we understand these cycles as the superposition of a number of different effects due to the Earth’s orbit, and it is known that it should not currently be affecting the climate, and in the long term (on geological scales) we would be heading towards colder climate anyway. Perhaps there are other cycles, but direct measures of the intensity of the sun are possible with satellites. and there is no trend which corresponds to the observed warming. You can see satellite measurements of solar radiation here, where we see that, apart from the 11-year cyclical variation, there is no long term trend, however looking at global temperature measurements in the same period at NASA’s site you will see that that temperature has been increasing over this period. Let me stress that I am not claiming that changes in solar radiation can’t have a large impact on climate, just that there is no evidence that they are responsible for the current changes. There is evidence on the other hand that a trend in solar radiation did contribute to warming in the early part of the 20th century for example. In fact, even if solar radiation was increasing now, this still wouldn’t negate what we know about the chemistry of C02 and it’s role in the atmosphere, it would just mean that both the greenhouse effect and solar radiation were having an effect, so there would still be good reason to act on C02 emissions. As it happens, direct observations can rule out the sun as causing major change at the present time.

Moving on, the next claim is that the amount of C02 that we emit is very small compared to the amount released through natural processes – degassing from oceans, release from other lifeforms, release from geological processes. My response here is that the absolute amounts are not the most important point, rather the variation. There is a natural cycle of C02, huge amounts are emitted and absorbed. Maybe our contributions are small, but due to the long atmospheric lifetime of C02 they accumulate. This is C02 which was taken out of the natural cycle millions of years ago, which we are removing from under the ground, so we are adding extra C02 to the system. Imagine a bucket with a small hole, and a tap dripping water into it – under equilibrium, where the same amount is going in from the tap as draining through the hole, then the level in the bucket would be constant. Now, suppose that you increase the flow of water by a relatively small, but still significant fraction of the amount you already have. While the extra flow is only a small contributer, if you end up with more going in than coming out the hole then the level will slowly rise. Given enough time you might have twice as much water contained in the bucket than what you started with – this is basically what has happened with C02. Over one year the amount may be small compared with the natural carbon cycle, but it is adding something extra to the system, and it is accumulating, so now we have a concentration of 380ppm compared with 280ppm in the pre-industrial era. Not double, but an increase by more than one third which is rather significant.
On the topic of volcanoes we can see what the US Geological Survey have to say:

Comparison of CO2 emissions from volcanoes vs. human activities.
Scientists have calculated that volcanoes emit between about 130-230 million tonnes (145-255 million tons) of CO2 into the atmosphere every year (Gerlach, 1999, 1991). This estimate includes both subaerial and submarine volcanoes, about in equal amounts. Emissions of CO2 by human activities, including fossil fuel burning, cement production, and gas flaring, amount to about 27 billion tonnes per year (30 billion tons) [ ( Marland, et al., 2006) - The reference gives the amount of released carbon (C), rather than CO2, through 2003.]. Human activities release more than 130 times the amount of CO2 emitted by volcanoes–the equivalent of more than 8,000 additional volcanoes like Kilauea (Kilauea emits about 3.3 million tonnes/year)! (Gerlach et. al., 2002)

Now Prof. Plimer goes on to refer to other geological processes which he claims are not taken into account in the usual calculations. This is his area of expertise, so his opinion should be of particular interest here (I have to admit, on the other hand, that my area of academic expertise will not be called upon, I can say with confidence that Bundle Gerbes are not responsible for global warming). He discusses earthquakes as a cause, I can’t really say much about the details of this, but one thing strikes me about this argument – these earthquakes, or other geological processes, would have to have increased to have contributed to the increased levels of C02 in the atmosphere. If they’d been going at roughly the same rate since pre-industrial times then they would simply elevate the “equilibrium level” (or the water level in our leaky bucket). While we would expect that a significant increase in earthquakes on land over this period would be well documented, the earthquakes on the deep ocean floor are another matter. This article gives an idea of the difficulties involved. So perhaps these could have increased without being noticed, and have played a significant role in the carbon cycle, but to the extent that we can disregard industrial emissions?
Well since I’m outside my field of expertise I’ll appeal to the experts at NOAA (National Oceanic & Atmospheric Adiministration)

· How do we know that humans are responsible?

The evidence for a dominating human role in the CO2 increase is extremely strong. The 36% increase (in 2006) in atmospheric CO2 observed since pre-industrial times cannot be explained by natural causes. CO2 concentrations have varied naturally throughout Earth’s history. However, CO2 concentrations are now higher than any seen in at least the past 650,000 years. Furthermore, the observed progressive depletion in carbon-13 (see the question below about isotopes) shows that the source of the CO2 is either fossil fuels or deforestation because produce CO2 depleted in carbon-13. The atmospheric CO2 increase cannot have come from the oceans because that would not have caused any depletion of carbon-13. In fact, carbon in the oceans has itself become gradually depleted, with the greatest depletion at the surface. That implies that the signal is imposed from the atmosphere. The next piece of evidence is that we also observe a depletion of radioactive carbon-14 in the atmosphere and oceans, with the strongest signal in the atmosphere suggesting it is the place where the depletion originates. Fossil fuels contain no carbon-14, and their combustion produces CO2 without carbon-14. Deforestation does not cause a change in atmospheric carbon-13. The observed depletion in the atmosphere and oceans is in fact quantitatively consistent with the amount of fossil fuels burned until now. Finally, annual mean CO2 concentrations in the northern hemisphere are higher than in the southern hemisphere, and more so in recent years compared to the early years of atmospheric CO2 measurements. This suggests a growing source of CO2 in the northern hemisphere, which is in fact where most of the fossil fuel burning takes place.

More on isotopes from the same source :

· Why are isotopes of greenhouse gases important?

Chemical and biological processes in nature, such as respiration, photosynthesis and atmospheric chemical reactions, often show very slight preferences for one isotope over another. For example, photosynthesis discriminates against the heavy 13C isotope, and plant matter and respired CO2 is therefore depleted in 13C relative to the atmosphere. Careful analysis of the isotopic composition of atmospheric trace gases can provide valuable information on the sources and sinks of the gases concerned because each natural process leaves its isotopic “signature” in the gases it produces.

This appears to provide conclusive evidence that for the most part the increase in C02 is due to the burning of fossil fuels. Interestingly it is possible to estimate just how much carbon has been released in this way. It would be interesting to look into the implications of that figure but I would like to get to the end of this post some time, so perhaps I’ll return to that later. To my knowledge it hasn’t been used in determining the attribution of C02 so it’s not really relevant here.

So overall there may be some additional geological effects that have not been factored in, but to claim that these effects dominate to the extent that human effects are negligible is an extraordinary claim which goes against a huge body of peer reviewed science. This does not make it incorrect, but there needs to be some serious evidence (Eg studies published in peer-reviewed journals) to back it up. Think about it, for Plimer’s thesis to be correct we have the following requirements:

  • The change from 280ppm to 380ppm of C02 in the atmosphere is predominately due to geological processes.
  • Thus these processes must be increasing their release of C02.
  • Overall there must be vastly more carbon entering the atmosphere than currently thought, since we are aware of the amount from fossil fuels, yet this is required to be small compared with these “geological emissions”.
  • Hence there must be much more C02 absorbed by natural processes than we currently think.
  • The geological emissions must have a similar isotopic composition to fossil fuels – there would have to be an explanation for this.

If this theory can be supported with evidence then so be it, but until then it hardly renders AGW as extremely unlikely. You would generally propose a new theory if there is some observation which cannot be explained by an existing theory, and your new theory should explain everything that the old one could, as well as fill the gap. I don’t see this theory achieving that here, it seems to raise more questions than it answers.
Next Prof. Plimer elaborates on his scepticism:

So I think my scepticism derives from the fact that if you ignore history, which we are doing, then to understand the present and the future we’re doing that very much at our peril. The arguments where we are being bombarded with information that humans are changing climate can only be valid if we ignore astronomy and if we ignore geology, and I argue that these arguments are not scientific because science is coherent, that a scientific hypothesis needs to be coherent with evidence from all quarters and that evidence has to be validated.

Do proponents of AGW ignore history? Try looking at the report by Working Group 1 of the IPCC in the AR4 titled The Physical Basis of Climate Change, specifically chapter 6 which is titled Paleoclimate. Here is a whole chapter looking specifically at the history of the Earth’s climate. Also worth looking at is Chapter 9: Understanding and Attributing Climate Change. Section 9.3 is titled “Understanding Pre-Industrial Climate Change” and is divided into subsections “Why Consider Pre-Industrial Climate Change?”, “What can be Learned from the Last Glacial Maximum and the Mid-Holocene?” and “What can be Learned from the Past 1,000 Years?”.
Perhaps Prof. Plimer has reason to disagree with their findings, but I cannot see how it can be claimed that AGW theory ignores history.
I’m not sure how astronomy comes into it though I can suggest a few possibilities. Firstly some critics claim that AGW theory ignores the sun, this is blatantly wrong, as solar forcings are an important part of climate models, and at a more fundamental level, it is the energy from the sun which is trapped by C02, causing warming. As mentioned above, direct observations show that solar variation does not match the observed change in climate, so while the sun may be the main driver of climate, it has been ruled out as the prime suspect in climate change. Secondly, there is the old “why is there global warming on Mars? Must be all those martian SUVs” argument … I don’t honestly believe that this is what he could be referring to, but if you want to know about it you can try here or here for details. I think the most likely candidate for how astronomy is left out of AGW theory is the cosmic ray theory of Svensmark which I have previously discussed here. Essentially it is a theory about how cosmic rays can play a role in cloud formation which has been backed up by experimental evidence. The problem is that it is a big leap from finding an additional influence on climate, and saying that it invalidates AGW. In particular, there is no observed change in the intensity of cosmic rays which would produce the observed change in climate. (Update: more at Bad Astronomy, via Deltoid)
So where is all the evidence from other scientific areas which contradicts AGW? The following cross-disciplinary scientific organisations don’t seem to be aware of it: Academia Brasileira de Cie�?ncias, Royal Society of Canada, Chinese Academy of Sciences, Acade�?mie des Sciences (France), Deutsche Akademie der Naturforscher, Indian National Science Academy, Accademia Nazionale dei Lincei (Italy), Science Council of Japan, Academia Mexicana de Ciencias, Russian Academy of Sciences, Academy of Science of South Africa, Royal Society (UK) and the National Academy of Sciences (USA). They recently jointly issued this statement . These are just the national scientific bodies of the “G8+5″, there are many others, including the Australian Academy of Science. This may bring accusations of “appeal to authority” (more on this later), but remember, I am examining the claim that climate scientists don’t incorporate expertise from other scientific fields – if this was true surely these organisations would notice? Their support suggests that climate science is mainstream science, accepted by the majority of scientists.
Prof. Plimer does give an indication of who the dissenting scientists that he has in mind are,

You would be very hard-pushed to find a large number of geologists who would argue that humans are creating modern climate change because in geology we’ve seen massive climate changes, we’ve seen sea levels go up and down like a yoyo.

I believe that the Geological Society of America would represent a large group of geologists. Here is their position statement on global climate change,

The Geological Society of America (GSA) supports the scientific conclusions that Earth’s climate is changing; the climate changes are due in part to human activities; and the probable consequences of the climate changes will be significant and blind to geopolitical boundaries. Furthermore, the potential implications of global climate change and the time scale over which such changes will likely occur require active, effective, long-term planning. GSA also supports statements on the global climate change issue made by the joint national academies of science (June 2005), American Geophysical Union (December, 2003), and American Chemical Society (2004). GSA strongly encourages that the following efforts be undertaken internationally: (1) adequately research climate change at all time scales, (2) develop thoughtful, science-based policy appropriate for the multifaceted issues of global climate change, (3) organize global planning to recognize, prepare for, and adapt to the causes and consequences of global climate change, and (4) organize and develop comprehensive, long-term strategies for sustainable energy, particularly focused on minimizing impacts on global climate.

Note that they accept the human role in climate change (though I would say that they downplay it compared with the other statements which they endorse). They also accept the need for action, in particular including the use of sustainable energy to minimise our impact on the climate. Like Plimer, they call for more study, and a better understanding from a geological point of view, but clearly they do not think that geological considerations cause any significant problem for the scientific consensus as presented by the IPCC. What’s more, there position is even less equivocal if you look at the background to the statement where they say

The geologic record provides a direct measure of the frequency, range, and duration of significant global climate changes throughout Earth’s history. Natural phenomena and processes have caused significant alterations of Earth’s climate. Of significance to the issue of modern global climate change are the interpretations of the geologic record showing that the rate of change in atmospheric composition, especially with respect to carbon dioxide and other greenhouse gases, is unprecedented in Earth’s recent history. Specifically, the carbon dioxide content of the atmosphere is higher than at any time in the past 650,000 years, and probably higher than at any time in the past 30 million years.

Clearly they are not of the opinion that current warming is the sort of business as usual that is suggested by Prof. Plimer, so his statements do not necessarily broadly reflect the opinions of his fellow geologists.

There is one large group of geologists at least who do appear to agree with him, they are the American Association of Petrolium Geologists. Their position statement agrees substantially with the overall points that Prof. Plimer makes, though the details are a little different. It seems, however that they have found more recent developments in the science persuasive, and they are working on a new statement which will does not reject the validity of AGW.

Returning to the quote from the interview, why should geologists disagree with AGW because they know how much sea level has changed in the past? This is a return to the point we started with (and there are similar references throughout the interview). Now I have a great respect for the work of geologists in reconstructing the history of the Earth, in fact I consider it one of the great achievements of science that we have such a detailed knowledge of things that happened in a past so distant that it is hard to really comprehend in terms of our lifetimes. However, this knowledge does not in any way contradict AGW. Nothing in AGW says that the climate hasn’t changed in the past, or that humans can only ever be the only major influence. If the geological record indicated a great degree of climate stability then in my opinion it would in fact weaken AGW. Climate does not change randomly, it happens for a reason. There have been all sorts of reasons proposed for past changes, but the important thing is that the geological record shows that the climate is sensitive to various factors and it is this which makes it plausible that human influence can effect climate. If it had always been stable in the face of orbital variations, changes in atmospheric conditions and so on, then it would indicate a very robust climate that could well stand up to whatever we throw at it.

Next there is a discussion of the CBC program “The Denial Machine” which has also screened on the Four Corners program on the ABC. Prof. Plimer was not convinced by their claims of a “denial lobby” which is funded to dispute the scientific evidence. I, on the other hand, was impressed. The quality of this program is largely a matter of opinion so my suggestion is that you follow the links and make up your own mind about the program.
There are many other claims about this “denial lobby” that you can assess, I would recommend DeSmogBlog as a good resource on this issue.
Finally he compares supporters of AGW to creationists in that they both appeal to authority to support their claims. It’s certainly true that Plimer is well acquainted with the arguments of creationists since he has been a well known critic of creationism. I just don’t see where the appeal to authority in AGW is. Perhaps the IPCC, but this is very different to an appeal to a deity, or to the authority of the bible. The IPCC is a summary of published research, citing the IPCC is no more of a creationist-style appeal to authority than if I say that the earth is about 4.6 billion years old. I have to trust the authority of the scientific consensus on that, I have not personally come to this conclusion through study of the evidence – but if I doubted it I could look through the scientific literature to understand how it works. Similarly, with AGW, I have not personally read all of the relevant papers (a formidable task!), and would not be qualified to judge all of them, but I can trust in the opinion of the IPCC and the various national academies. Where I want to know more detail I can look it up, as I have done at various points in this post. You see I can trust these sources because I know about their methods, and really I’m not putting faith in what these people say, rather I just need faith in why they say it – that their opinions are based on multiple peer reviewed papers in reputable journals, which have employed the scientific method. Sometimes this faith is misplaced, scientific frauds and have been perpetrated, and there have been honest mistakes, but over time these are corrected.
Let’s consider the alternative that Prof. Plimer gives us. We have to accept his claims that all of this is wrong for geological reasons, which it seems, are not acknowledged by major scientific academies, or even the Geological Society of America. Now maybe he’s right and they’re wrong but he is essentially appealing to his own authority as a geologist. He indicates that from the point of view of a geologist it is very hard to believe that AGW theory is correct. As a Professor of Geology he is well qualified to make such a claim, and we should place significant value in his opinion, but this is about science. It is often complicated and you might have to trust the opinion of an expert, yet if you’re not convinced you can always look to the evidence, as Plimer himself suggests, and as I have done in this post. I don’t believe that the available evidence supports the claims that he has made with regard to the validity of AGW theory.
I think the question of “appeal to authority” deserves a little more thought before I conclude. When I made an appeal, for example, to the expertise of NOAA this was an appeal to authority, but very different to a creationist saying that the Earth is 6000 years old because the bible says so. NOAA provide logical arguments to back up their claims, and you can follow these arguments right down to the original scientific papers if you feel the need. If you did this because something appeared to be wrong, or perhaps wasn’t completely consistent with new evidence then new results could be published, and no doubt NOAA would update their information. With the creationist, there is no logical argument, no scientific method, simply an appeal to infallible and unquestionable authority, and no amount of evidence will have an effect on the claim.

8 Responses to “Ian Plimer on the Science Show”

  1. Brian Bahnisch says:

    Great post. I followed you here from Quiggin’s.

    If you don’t mind me saying so, I think you are being kind to Plimer. To me it seems clear that he hasn’t really gotten his head into the issue of AGW.

  2. C. Allen says:

    Kind of makes you wonder about the legitimacy of any work that Professor Plimer has ever engaged in doesn’t it. I mean, setting aside for a moment the particular topic under discussion, the thought processes and methodologies he uses don’t really resemble anything most scientists would consider to be legitimately part of the scientific method. Sad really.

  3. Dylan Nicholson says:

    Hi, Stu

    I was actually planning to write an article about Ian’s views myself…looks like you’ve done 90% of the work though.

    I’m currently attempting to assess his claim that there is little consensus among geologists re AGW, via an e-mail survey of geologists currently working in Australia. So far he’s right, but admittedly I’ve only had 6 replies!

    I’d also like to clarify what his concern about CO2 release from earthquakes really is, and determine his exact connection to the IPA.

  4. R2D2 says:

    “The 1940-76 decrease is explained by the effect of particles from industrial pollution reflecting sunlight back into space”

    You state this as if it is a proven fact, then reference a shoddy web page. Do you have any evidence for this?

    I think the point about explanation of natural variation is important. Regardless of the magnitude, the climate has always experienced natural variation. It must be experiencing some level of natural variation today.

    Today the aim is to measure anthropogenic global warming, the hypothesis is this is significant and positive and the null is that this is zero.

    The first task is then to remove natural warming from the last centaury, and then to place a confidence interval on anthropogenic warming in order to reject the null.

    We therefore need to understand natural climate change before we can prove the existence of anthropogenic global warming, until then it is only a theory.

  5. Stu says:

    My point was that it was disingenuous to suggest that the cooling during that period was unexplained when there is a standard explanation for it. Perhaps the standard explanation is wrong, but if Plimer had good reason to believe this why pretend that there is no explanation?
    I take issue with the description of Real Climate as a “shoddy web page”. I was addressing the point that climate scientists supposedly do not bother explaining various historical changes in climate. I linked to a blog run by climate scientists, in particular a post by a chemist who studies the effect of aerosols on climate. I feel that this is an appropriate response.
    The evidence that you ask for was not really the point in this case, as it wasn’t the details of the explanation for the mid-century cooling that was brought into question, rather it was its very existence. I demonstrated that climate scientists do indeed have an explanation for this and various other features of the historical climate. The diagram in the real climate post (from the IPCC AR4) is of particular interest, it shows the relative impact of various forcings on the climate. This shows the way to go if you do want to see the evidence – the IPCC AR4.
    This report summarises a huge effort that has gone into explaining how the climate is determined by various factors and distinguish anthropogenic effects from natural ones. Chapter 9 on Understanding and Attributing Climate Change is of particular interest. Section 9.2 on Radiative Forcing and Climate Response has a subsection 9.2.3 Implications for Understanding 20th Century Climate Change. Section 9.4 is on Understanding Air Temperature Change During the Industrial Era.
    The effect of aerosols is well understood. Volcanic eruptions have shown and quantified the cooling effect they have. Also their chemical properties can be studied, by observation in the lab, and by analysis of their molecular structure. The cooling effect of aerosols is not in any way controversial, neither is the fact that lots more of them were put into the atmosphere by industrial activity in the mid 20th Century, and that they decreased after pollution controls were introduced in the 1970′s. Using the basic science of aerosols, greenhouse gases and other forcings (as shown in the linked diagram) climate scientists make models of the climate. They test them by hindcasting, i.e., run the models with historical forcings as input and compare outputs with historical data. Doing this, the aerosol induced cooling is replicated in the models. Another feature is that the post 1970′s warming is not shown without the forcing provided by greenhouse gases.
    A historical perspective on how these ideas were developed is given by Spencer Weart in his book The Discovery of Global Warming, particularly the sections on aerosols and the modern temperature trend.
    One final point, you are right that there is no proof that aerosols caused the mid-century cooling. There is also no proof of Newton’s Laws of motion, Darwin’s theory of evolution (as creationists like to point out), the Germ Theory of Disease (popular with Chiropractors), Einstein’s theory of relativity (most physics cranks) or any other scientific theory. Proofs belong to mathematics, not science. There is however an abundance of evidence which is the best you can hope for in science.

  6. I debunked some claims that evidently were based on Plimer’s book at Australian prime minister Kven Rudd’s blog, and repeated the main ones at my personal blog. Since I haven’t read the book, I’m ready to be corrected but since no one has so far, I assume the person I was correcting was quoting correctly from the book.

    I’d appreciate it if someone who has read the book would mosey over to Opinionations and let me know if the comments I quoted are an accurate representation of the book. If so, it’s pretty shocking; this is stuff someone has quoted to support their argument that climate change is a hoax and made a right fool of themselves.

  7. Les Cook says:

    I have just read Plimer’s book. It was clearly rushed to print and needed better editing, but it is still an impressive review of a large area of scientific research (over 2300 references, mostly to peer reviewed articles in respectable journals. I am an (ex) physicist and computer modeller and feel comfortable evaluating research papers. I arrived at this site looking for a rebuttal of the book, but I have not yet found anything rigorous enough to be convincing. I would welcome references to such material if it based on the content of the book, not a lay description in a TV program.

  8. Stu says:

    Les, this post is not about Plimer’s book, it was written two years ago, well before the book was published (in fact I didn’t even know then that he was writing one). It is also not about a TV program. It is in response to claims made by Plimer in a radio program, as given in the transcript (linked in the post).

    More recently I have written some posts about the book. I have not written a review or rebuttal (since I haven’t read his book), rather I have chiefly just commented on the press coverage, however I have also linked to a number of other websites containing detailed reviews and rebuttals which clearly show that it is not simply an editing issue.
    The most relevant post would be Details of Heaven and Earth, and the numerous links therein. Also Geological Timescales and the Effects of Climate Change and the follow-up More Reactions to the SMH Piece.

    I will be particularly interested to see how Plimer answers these questions from George Monbiot.