Summary. Coordinated  by the IPCC a great number of climatologists world-wide have put a great deal of effort over a number of years into producing and refining simulation models of climate change. Lomborg questions the ability of these models to match actual temperature changes. He presents a graph of a model simulation which includes only the greenhouse effect, not the natural variations, in order to "show" that the IPCC climatologists are very far from reproducing the actual temperature course. He has also studied other IPCC simulations where the effects of natural variations and the effect of the man-made greenhouse effect are combined with the result that the temperature course up to now is replicated quite well, demonstrating that the models have recently become so well refined that they reflect reality to a high degree. But instead of showing graphs that demonstrate a good fit to reality, he only reproduce those that demonstrate a bad fit, by insisting that graphs combining natural and man-made effects should not be presented in his text.
    Lomborg, who has no expertise in this area himself, tries at great length to undermine confidence in those experts who have worked in the field for many years. He derogates those experts by whom he should have been peer reviewed - and was not !

    In discussing the effects of man-made greenhouse gases on global temperatures, Lomborg does not deny that there may be an effect, but he does all he can to make the effect look as insignificant as possible. One way of doing this is to undermine confidence in the work of the International Panel on Climate Change - IPCC. IPCC is an institution that co-ordinates climate research world-wide: It is a forum where scientists communicate, discuss simulation models, and constantly refine them. Thereby they gradually improve their understanding of what factors are important for the temperature course and what are their relative contributions, and obtain better and better predictions of what will happen in the future. During the late 1990s, for instance, IPCC improved its models by including the effects of sulphate aerosols in the atmosphere.
    In figure 138, on page 267, Lomborg purports to demonstrate that the IPCC models come nowhere near close to simulating the actual temperature course up to now. First there is a curve which does not include the effect of sulphate aerosols, and this curve obviously overshoots the mark - it predicts too much warming. Then there are two curves that include the effect of sulphate aerosols, and these simulate the general trend quite well. Even these curves are strongly criticized by Lomborg, however, although I will not here go into detail with his criticism (see notes to p. 268). Lomborg says that in the finer details, these curves do not simulate the actual fluctuations in temperature very well. He writes (p. 267): " . . the rapid temperature increase from 1910 to 1945 is still left unexplained". At this point he inserts note 2172, which refers to IPCCs authoritative report from 2001, including their figure 12.7.
    Now, if one studies IPCC´s figure 12.7, which Lomborg obviously must have done, you see that IPCC has actually been able to simulate the temperature course up to now surprisingly well. The figure is in three parts, one which shows the contributions form natural causes (a), one which shows the contributions from manmade courses (b), and finally one which combines the two (c).
   I reproduce the figure here below. Each graph shows the deviations from the average temperature during the years around 1900. In all three graphs the actually observed temperatures are represented by the red curve, and a number of runs of the model simulations are shown with black curves. The idea of showing several black curves is to give an impression of the degree of uncertainty in the model predictions.

In chart (a) we see that the increase in  temperatures during the period 1920-1960, relative to 1900, is simulated well. This means that natural fluctuations - for example. in the energy of the sunlight and in the amount of dust from volcanic eruptions - can indeed explain some of the variation. But overall, the degree of prediction is poor. We note especially that the unprecedented temperature rise during the last 20 years cannot be explained by natural courses - on the contrary, natural causes would have given a slight cooling. Chart (b) gives the effect of anthropogenic, i.e. manmade, causes, including sulphate aerosols. Here, the temperature rise during the last 20 years is simulated quite well, whereas there is considerable deviation from the actual (red) curve during the temporary rise from 1920 to 1960. This is the type of simulation that Lomborg criticizes, telling us that it demonstrates that the modellers in IPCC are not able to simulate the actual temperature fluctuations very well. Chart (c) shows the result of combining both natural and manmade causes into the model. In this case the black curves fit the red curve both during the temporary increase in the period 1920-1960 and during the sharp rise from 1980 onwards. The conclusion is that the present understanding of what affects the temperature is sufficient to explain most of the observed fluctuations. It seems obvious that the global temperature is affected by natural as well as manmade causes, but the temperature rise from 1980 onwards is due only to manmade causes. As the level of greenhouse gases is still increasing, it is obvious that the temperature will rise even faster during the next decades.

Now, let us return to Lomborg´s treatment of the subject. He has seen the above figures, and could have presented them in his book. If he had done that, he would have given his readers the impression that the scientists in IPCC have now got a good understanding of what is happening, and have models which simulate the actual situation quite well. Instead, he chooses to bring his figure 138 which gives the opposite impression, viz. that models based on the emissions of greenhouse gases are far from simulating the actual situation, and hence that the scientists do not understand what is happening. This may be contrasted with his figure 146 on p. 277 which suggests that those scientists who focus on natural causes are good at simulating the actual situation. So the reader will get the impression that natural causes may explain a lot, whereas manmade causes explain only little. At the bottom of page 277, he writes: "This theory [the sunspot theory] also has the tremendous advantage, compared to the greenhouse theory, that it can explain the temperature changes from 1860 to 1950, which the rest of the climate scientists with a shrug of the shoulders have accredited to `natural variation´". Knowing that Lomborg has actually seen and studied IPCC´s figure 12.7, this text must be characterized as delliberately misleading.
    At the start of the next page (p. 278), Lomborg admits that the natural causes fail to explain the temperature rise during the last 10-30 years. He says: "Most likely we are instead seeing an increasing signal, probably from greenhouse gases like CO2." This is certainly an understatement of what we know. But in order further to minimize the significance of this rise, he continues: ". . the fact that the emerging greenhouse gas signal only appears now seems to indicate once again that the estimated CO2 warming effect needs to be lowered." Once again we must say that Lomborg is deliberately misleading, as we know that Lomborg has studied IPCC´s figure 12.7, in which the slope of the recent rise fits fairly well with what the slope predicted from the level of greenhouse gases.
    The whole of Lomborg´s chapter on global warming is permeated with such bias. On page after page he does all he can to undermine the credibility of the majority of climate scientists in the world - hundreds of scientists who through years of constant trial and error, carefully checked by colleagues in a very thorough peer review process, have gradually achieved a reasonably good understanding of the very complicated temperature balance. He himself, on the other hand, is not a specialist in the field, and has not been subjected to any peer review by those who are. On this basis, no-one would have taken Lomborg´s writings seriously had they not been forced to do so by the political backup he recieves. Lomborg has damaged science by replacing the scientific truth with the "truth" of what is politically expedient.