‘The Great Global Warming Swindle’: Five major misrepresentations of the scientific evidence and researchers’ interpretations in the DVD version
The DVD version of ‘The Great Global Warming Swindle’ has been available for purchase since late July 2007. The front of the presentation case describes it as a “documentary”, which is defined by the Oxford English Dictionary as “a film or television or radio programme giving a factual account of something, using film, photographs, and sound recordings of real events”. However, the DVD contains at least five major misrepresentations of the scientific evidence and researchers’ views on climate change. This document presents details of the five misrepresentations.
Misrepresentation 1: Global average temperature today is not as high as it was during other times in recent history, such as the Medieval Warm Period, indicating that the recent warming trend is a natural phenomenon.
The DVD version of the programme presents a graph that is labelled “Temp – 1000 Years”, which is attributed to the “IPCC” [Intergovernmental Panel on Climate Change]. This graph purports to show global average temperature between 900 AD and “now”, with the highest values recorded between about 1100 and 1300 (labelled as “Medieval Warm Period”). The label “now” on the far right side gives the impression that the graph shows temperature up to the present day.
As Martin Durkin, the programme’s producer, admitted in an exchange of e-mail messages in April (the text of which are accessible at www.climateofdenial.net), the graph appearing in the DVD version of the programme is based on a figure that was originally published by Hubert Lamb in 1966, and which was subsequently reproduced in a 1975 report by the United States National Research Council (NRC), and in the First Assessment Report of the IPCC in 1990.
It is obvious that a schematic diagram that was originally published in 1966 cannot possibly show global average temperature over the last 40 years, and so the label “now” appearing on the graph in the DVD version of the programme is a false and inaccurate modification.
The figure produced by Lamb also pre-dates all of the research on the global temperature record that has taken place since 1966. It has been superseded by a number of more up-to-date temperature reconstructions for the last millennium, which were reviewed in a report published last year by the NRC for the United States Congress, in response to the so-called ‘hockey stick’ controversy. The report concluded that “none of the large-scale surface temperature reconstructions show medieval temperatures as warm as the last few decades of the 20th century”. It acknowledged that parts of the Earth may have been warmer at points over the past 1000 years, but that these regional trends were not global in extent. The report also included a reproduction of Lamb’s 1966 figure as it appears in the IPCC First Assessment Report, and noted that “[t]he pronounced warming trend that began around 1975 was not indicated in the graphic”.
The NRC report also pointed out: “Surface temperature reconstructions for periods prior to the industrial era are only one of multiple lines of evidence supporting the conclusion that climatic warming is occurring in response to human activities, and they are not the primary evidence”.
In summary, the DVD version misrepresents an out-of-date figure, published originally in 1966, to make it appear as if it records global average temperature up to the present day. The claim made in the DVD version of the programme that the recent warming of the Earth is a natural trend that has been seen before in the last 1000 years is not supported by the scientific evidence.
Misrepresentation 2: Global average temperature decreased between about 1945 and 1975, and increased more before 1945 than in the past few decades, indicating that the steady rise in atmospheric concentrations of greenhouse gases cannot be responsible for the warming.
The DVD version of the programme presents a graph with the title “Temp – 140 years”, attributed to the “IPCC”. The graph covers the period between 1860 and 2000. It shows approximately constant temperature between 1860 and 1910, a rise up to about 1945, then a very slight decrease to about 1975, and a final rise up to 2000. The narrative highlights the rise between 1910 and 1945 and claims that this represents the largest rise in global average temperature over the last 150 years. It also highlights the slight decrease between 1945 and 1975 and notes that this occurred during the period after the World War II when emissions of greenhouse gases increased markedly.
This appears to be a graph reproduced from the IPCC Third Assessment Report, published in 2001. An updated version of this graph was published early in 2007 in the IPCC Fourth Assessment Report, with the temperature record extended up to 2006. As this latter report indicated, the global temperature for the period 2001-2005 was 0.76+/-0.19۫C higher than for 1850-1899, and the temperature increase between 1910s and the 1940s was 0.35۫C compared with a rise of 0.55۫C between the 1970s and the present. Hence the claim made in the DVD version of the programme that most of the warming over the last 150 years occurred between 1910 and 1945 is factually incorrect.
In addition, the IPCC Fourth Assessment Report also concluded that “[h]uman activities have also caused increased concentrations of fine reflective particles, or ‘aerosols’, in the atmosphere, particularly during the 1950s and 1960s”. These aerosols included sulphates that are produced from sulphurous impurities in oil, gas and coal. As a result, “[d]uring the 1950s and 1960s, average global temperatures leveled off, as increases in aerosols from fossil fuels and other sources cooled the planet”, and the “rapid warming observed since the 1970s has occurred in a period when the increase in greenhouse gases has dominated over all other factors”.
However, the DVD version of the programme does not make any mention of the impact of atmospheric aerosols on the record of global average temperature. The producer of the programme, Martin Durkin has attempted to justify this by suggesting that if aerosols caused the cooling between 1945 and 1975, then global average temperatures should be lower today, because he believes that atmospheric concentrations of aerosols should be even higher today than they were during that period. But the IPCC Fourth Assessment Report pointed out that “[g]lobal sulphur emissions (and thus sulphate aerosol forcing) appear to have decreased after 1980”.
In summary, the DVD version of the programme misrepresents the record of global average temperature by stating that most of the warming during the last 150 years occurred before 1945, rather than after 1970. It also misrepresented the current state of scientific knowledge by failing to mention that the cooling effects of aerosol need to be taken into account when considering the period of slight cooling between 1945 and 1975.
Misrepresentation 3: Models of anthropogenic climate change are inconsistent with the data because the surface is warming at a faster rate than the troposphere, indicating the increasing greenhouse gas concentrations cannot be responsible for the rise in temperature.
The DVD version of the programme stated that all models of the increase in global average temperature due to a rise in the concentration of atmospheric greenhouse gases indicate that the troposphere should warm faster than the surface, but the data shows that the surface is warming more quickly. This is untrue. In 2006, the US Climate Change Science Programme (USCCSP) published a review of the scientific evidence on temperature trends in the lower atmosphere. It pointed out that for global averages, the recorded temperatures show greater warming trends in the troposphere compared with the surface. However, since 1979, most data sets show a slightly greater warming at the surface. The report indicated that for temperatures since 1979, “the range of recent model simulations is almost evenly divided among those that show a greater global-average warming trend at the surface and others that show a greater warming trend aloft”. It concluded that “[g]iven the range of model results and the overlap between them and the available observations, there is no conflict between observed changes and the results of climate models”. One of the lead authors on this report was John Christy, who was portrayed in the programme as supporting the notion that the models are not consistent with data.
The USCCSP report acknowledged that on decadal and longer time scales, model simulations for the tropics show that the troposphere should warm more quickly, but the data records a faster increase in surface temperatures. It suggested that “non-climatic influences remaining in some or all of the observed tropospheric data sets lead to biased long-term trends”.
This finding was reinforced by the IPCC Fourth Assessment Report, based on a review of the worldwide scientific literature, which concluded:
“For global observations since the late 1950s, the most recent versions of all available data sets show that the troposphere has warmed at a slightly greater rate than the surface, while the stratosphere has cooled markedly since 1979. This is in accord with physical expectations and most model results, which demonstrate the role of increasing greenhouse gases in tropospheric warming and stratospheric cooling; ozone depletion also contributes substantially to stratospheric cooling.”
In summary, the DVD version of the programme wrongly claims that the records of surface and tropospheric temperature are inconsistent with each other and with models for anthropogenic climate change. It also failed to explain the likely cause of discrepancies relating to the tropics.
Misrepresentation 4: Ice cores show that during earlier periods in the Earth’s history, rises in carbon dioxide followed increases in temperature, and therefore the current rise in greenhouse gas concentrations cannot have caused the recent increase in global average temperature.
The DVD version of the programme presents a graph with the title “Temp and CO2”, attributed to “Caillon et al”, for period from about 237,500 to 240,500 years ago. It shows two lines, one for CO2 and the other for temperature, and highlighted a gap between peaks in both curves of 800 years. This graph appears to be based on a paper by Nicolas Caillon and co-authors which was published in the journal ‘Science’ in March 2003. The axis labelled as “Temp.” on the programme’s graph actually uses a scale for isotopic argon composition, rather than temperature, like the corresponding graph in the paper.
The paper by Caillon and co-authors examined the timing of changes in atmospheric carbon dioxide and temperatures during the Termination III deglaciation event about 240,000 years ago. The main finding of the paper was that “[t]he sequence of events during Termination III suggests that the CO2 increase lagged Antarctic deglacial warming by 800+/-200 years and preceded the Northern Hemisphere deglaciation”. Although the narrative for the DVD version of the programme correctly reported the 800-year lag, it wrongly suggested that this meant the rise in carbon dioxide concentration had no impact on global average temperature.
In fact, the paper by Caillon and his co-authors concluded that a fluctuation in the Earth’s orbit (and hence its distance from the Sun) initiated the increase in surface temperatures in Antarctica, and was followed by a gradual warming of the oceans, which released substantial volumes of carbon dioxide that was dissolved in the sea water. The paper also indicated that the carbon dioxide released by the oceans added to the warming of the atmosphere, and contributed to the deglaciation of the Northern Hemisphere. It stated that the sequence of events during the Termination III deglaciation is “still in full agreement with the idea that CO2 plays, through its greenhouse effect, a key role in amplifying the initial orbital forcing”.
The DVD version of the programme ignored descriptions of the role that carbon dioxide has played in changes in temperature during glacial and interglacial cycles that have been published in scientific journals, such as the paper by Claude Lorius and co-authors which appeared in ‘Science’ in 1990. It explained that the fluctuations in the Earth’s orbit are “relatively weak when considered on an annual globally averaged basis”, and must have been amplified by changes in atmospheric concentrations of carbon dioxide and methane to have resulted in the global patterns of warming and cooling that are contained in the geological record.
In summary, the DVD version of the programme misrepresents the conclusions of the paper by Caillon and his co-authors by suggesting that the 800-year lag proves that rising carbon dioxide levels did not contribute to the increase in temperatures during deglaciation. It misrepresents the state of current scientific knowledge by failing to acknowledge research findings that rising carbon dioxide concentrations amplified the warming during deglaciations that were initiated by fluctuations in the Earth’s orbit.
Misrepresentation 5: The variation in global average temperature since industrialisation is due to solar activity instead of the rise in atmospheric concentrations of carbon dioxide and other greenhouse gases.
The DVD version of the programme presents a graph with the title “Temp & Solar Activity: 120 Years”, and attributed to “Friis-Christensen and Svensmark”. The scale extends between 1860 and 2000 and shows a line for “Temp.” between 1860 and about 1982, and for “Solar” between 1860 and about 1975. There appears to be a reasonably good correspondence between the two lines for the period between 1860 and 1975.
This graph appears to be based on a figure from a paper by Eigil Friis-Christensen and Henrik Svensmark, which published in the journal ‘Advances in Space Research’ in 1997. The figure in the paper showed “11-year average values of the Northern Hemisphere Land temperature (T) and the length of the solar cycle (L)” (with solar cycle length plotted on an inverse scale). The paper indicated that the figure was based on data reported in a paper published by Friis-Christensen and Knud Lassen in the journal ‘Science’ in 1991, and stated that “a comparison with the Northern Hemisphere land temperature during the last 130 years did show a remarkably good correlation with the smoothed curve of the varying solar cycle length indicating that this parameter was possibly a better indicator [than smoothed sunspot number] of a solar cycle activity variations that could affect the Earth’s climate”.
However, the DVD version of the programme failed to mention any of the subsequent studies that report measurements of solar activity since 1975. For instance, Paul Damon and Alexei Peristykh published a paper in the journal ‘Climatic Change’ in 2005 which showed sunspot cycle length (on an inverse scale) against the temperature of the Northern Hemisphere between about 1700 and 2000. The paper shows that the filtered values of sunspot cycle length have decreased only slightly since 1976 and are still longer than in 1950, while Northern Hemisphere temperature has increased sharply since about 1970. The authors calculated that known solar periodicities accounts for 18 per cent of 20th century warming to 1997. They concluded that “[a]lthough our model demonstrates that solar forcing is not a dominant cause of 20th century Northern Hemisphere warming, it demonstrates that it could produce a very significant forcing of pre-industrial climate”.
Furthermore, the programme failed to point out that the length of a sunspot cycle has not been demonstrated to provide a good indication of the Sun’s energy output. A recent review of the scientific literature by Peter Foukal and co-authors, published in the journal ‘Nature’ in 2006, drew attention to the fact that the proper measure of the Sun’s total contribution to the temperature on Earth is “the wavelength-integrated radiation flux illuminating the Earth at its average distance from the Sun, called the total solar irradiance (TSI)”. The authors stressed that observations of sunspot cycle length “lack a demonstrated connection to TSI variation”.
Precise measurements of TSI have been possible through satellite-borne radiometry since the 1970s, and as the paper by Foukal and his co-authors makes clear, “the variations [in TSI] measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years”.
In addition, the programme failed to point out that, as the reviews of the scientific literature by the IPCC have shown, the variation in global average temperature since the Industrial Revolution can only be reproduced by models that take into account all natural and man-made factors. A paper by Gerald Meehl and co-authors in the ‘Journal of Climate’ in 2004, for instance, confirmed previous studies that showed the rise in global average temperature between the early 1900s and 1940s was “caused mostly by solar and volcanic forcing”, while the increase in temperature since the late 1960s was caused “mostly by the increase of greenhouse gases (partially offset by aerosol cooling)”.
The DVD version of the programme also ignored a paper by Mike Lockwood and Claus Fröhlich, which was published in June 2007 in ‘Proceedings of the Royal Society A’. The authors were prompted by the broadcast of the programme on Channel Four in March 2007 to review the evidence for solar activity driving the recent rise in global average temperature. They found, after examining all of the available evidence, that there are some “detection-attribution studies using global climate models that suggest there was a detectable influence of solar variability in the first half of the twentieth century and that the solar radiative forcing variations were amplified by some mechanism that is, as yet, unknown”. However, they also concluded that “the observed rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanisms is invoked and no matter how much the solar variation is amplified”.
In summary, the DVD version of the programme clearly misrepresents the current state of scientific knowledge by suggesting that solar activity explains the rise in global average temperature since industrialisation, and particularly in the past few decades.
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