‘The Great Global Warming Swindle’: Misrepresentations of scientific evidence and researchers’ interpretations
30 March 2007
On 8 March 2007, ‘The Great Global Warming Swindle’ was broadcast in the UK on Channel Four television, and over the following two weeks was broadcast again on the More 4 television channel. This programme, which Channel Four spokespersons have described in official statements as a “polemic”, claimed that the rise in global average temperature since the start of the Industrial Revolution has not been caused by the rise in atmospheric concentrations of carbon dioxide (CO2) and other greenhouse gases due to human activities, and instead can be explained by variations in solar activity. The narrative made a number of claims, supported by commentary from scientists and non-scientists, about the results and conclusions of research on climate change. Many of these claims misrepresented the scientific evidence and interpretations that have been documented by researchers through peer-reviewed papers. As such, these claims represent violations of Section 5.7 of the Ofcom Broadcasting Code, which states: “Views and facts must not be misrepresented”.
This document outlines seven of the major misrepresentations of the scientific evidence and interpretations that occurred in the programme.
Claim: 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.
Misrepresentation: The programme supported its claim that temperatures were higher in the recent past with a graph that was labelled “Temp – 1000 Years” and attributed to the “IPCC”. This graph purported 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”).
This was a clear misrepresentation of a diagram published by the Intergovernmental Panel on Climate Change (IPCC) in its First Assessment Report in 1990. The schematic diagram published by the IPCC showed global temperature variations from 900 AD to 1975 (ie it omitted the record of global average temperature after 1975). This graph has been superseded by numerous studies in the last 17 years, and the IPCC published updated records of global average temperature in its Second Assessment Report in 1995, its Third Assessment Report in 2001, and its Fourth Assessment Report in 2007.
The United States National Academies published a report in 2006 that reviewed the published scientific evidence on surface temperature reconstructions for the last 2000 years. It found that “[e]vidence for regional warmth during medieval times [centered around AD 1000] can be found in a diverse but more limited set of records including ice cores, tree rings, marine sediments, and historical sources from Europe and Asia, but the exact timing and duration of warm periods may have varied from region to region, and the magnitude and geographic extent of the warmth are uncertain”. Based on a review of the scientific literature, 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.”
By ignoring all of the papers detailing these reconstructions, the programme misrepresented the scientific evidence about long-term trends in global average temperature.
Claim: Global average temperature decreased between 1940 and 1980, and so could not depend on atmospheric concentrations of greenhouse gases, which increased over this period.
Misrepresentation: The programme broadcast on 8 March on Channel Four presented a graph, attributed to “NASA”, purporting to show “World Temperature – 120 Years” between about 1878 and 2002, plotted against some unspecified measurement of temperature change ranging in value from about -0.05 to 0.70. The graph showed an almost continuous decrease in temperature between about 1947 and 1976.
However, this graph does not correspond to any figure for global average temperature that has been published by NASA, and differs significantly from the graphs appearing in its recent publications and on its website (see: http://data.giss.nasa.gov/gistemp/graphs/).
In a subsequent broadcast on More 4 on 12 March, the programme presented a slightly different version of the graph instead, with the title “World temperature – 110 Years”. Compared with the graph in the earlier programme, the misattribution to NASA was omitted (but not replaced with any other attribution), and the scale of the x-axis was altered such that the graph covered the years from 1880 to about 1990. Despite this change in the x-axis scale, the shape of the plot remained the same as originally broadcast, such that the apparent decline in “World Temperature” was this time shown to occur between about 1940 and 1967. This graph corresponds very closely to Figure 12 of a paper by Arthur Robinson and Zachary Robinson of the Oregon Institute of Science and Medicine, with co-authors Sallie Baliunas and Willie Soon of the George C. Marshall Institute, which was published in the September/October 1998 issue of ‘Medical Sentinel’. A version of this paper is posted on a website set up by Arthur Robinson to accompany a petition against the participation of the United States in the Kyoto Protocol.
Measurements from meteorological stations that have been published by NASA and other agencies show that the there was an overall slight decline in global average temperature between about 1940 and 1976, but much less than that shown on the graph presented in the programme. The two different versions of the graph purporting to show “World Temperature” in the programme most closely resemble plots published by NASA and other organisations for average temperatures in the Northern Hemisphere, and particularly North America. However, graphs of average temperature in the Southern Hemisphere show overall increases during the period between 1940 and 1976, albeit at a lower rate than the periods immediately before and after.
It has been well-established in the scientific literature that the period of cooling that was most evident over North America and Europe between about 1940 and 1976 was largely due to increased concentrations of aerosols (particularly sulphates) released into the atmosphere by industrial processes, such as the combustion of coal. These aerosols lowered the amount of solar radiation reaching the Earth’s surface, for instance by scattering sunlight. The concentrations of these aerosols have been shown to be highest in the Northern Hemisphere, close to their industrial sources. A paper by David Stern, published in the journal ‘Chemosphere’ in 2005, showed that sulphurous emissions around the world increased sharply between 1945 and about 1989, since when they have declined markedly. Sulphuruous emissions peaked in North America and Europe during the 1970s.
Models that take account of natural factors, such as solar activity and volcanic aerosols, as well as anthropogenic factors, such as greenhouse gas emissions and aerosols from industrial processes, are able to reproduce the record of global average temperature over the twentieth century. The accuracy of the model results is reduced when the effects of man-made aerosols are removed.
By failing to even mention the effects of man-made aerosols, the programme misrepresented the scientific evidence on the causes of changes in global average temperature during the 20th century.
Claim: Models of the increase in global average temperature due to a rise in the concentration of atmospheric greenhouse gases suggest that the troposphere should warm faster than the surface, but the data shows that the surface is warming more quickly, indicating that anthropogenic climate change is not occurring.
Misrepresentation: The programme implied that the recorded changes in global average temperature of the surface and troposphere are inconsistent with the models. This is untrue. Much of the data for atmospheric temperature are consistent with models that include the impact of rising greenhouse gas concentrations due to emissions from human activities. 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”.
Hence, the programme wrongly suggested that the models and recorded data are inconsistent for global average temperature, and failed to explain the likely cause of discrepancies relating to the tropics.
Claim: Volcanoes produce far more carbon dioxide than human activities, so anthropogenic greenhouse gases cannot be having a significant effect on global average temperature.
Misrepresentation: The programme’s claim that volcanoes produce more carbon dioxide than human activities is simply untrue. It is difficult to know on what this claim is based as the programme did not cite a source. However, a paper by Nils-Axel Morner and Giuseppe Etiope, published in the journal ‘Global and Planetary Change’ in 2002, estimated that the lower limit for global subaerial volcanic degassing of carbon dioxide is 300 million tonnes per year. By comparison, Gregg Marland and colleagues at the Carbon Dioxide Information Center, Oak Ridge laboratory, estimated that 26,778 million tonnes of carbon dioxide were emitted by human use of fossil fuels in 2003. Therefore although Morner and Etiope described their estimate of carbon dioxide emissions from volcanoes as “conservative”, it is less than 2 per cent of the annual emissions of carbon dioxide from human use of fossil fuels.
Clearly the programme misrepresented the scientific evidence about the volumes of carbon dioxide that are released into the atmosphere by different sources.
Claim: 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 has not caused the recent increase in global average temperature.
Misrepresentation: It is well established that analyses of ice core from Antarctic show that local temperature rises during the transition from glacial to interglacial periods, which are triggered by regular fluctuations in the Earth’s orbit (and hence its distance from the Sun), were followed some time later by increases in the local average concentration of atmospheric carbon dioxide by up to 100 parts per million. However, the conclusion drawn in the programme that this means the recent rise on concentrations of carbon dioxide and other greenhouse gases could not be responsible for the recent increase in global average temperature is counter to the evidence presented in the scientific peer-reviewed literature.
In particular the programme misrepresented the contents of a paper by Nicolas Caillon and co-authors which was published in the journal ‘Science’ in March 2003. 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 authors found 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”.
The programme presented a graph to illustrate the results of the work by Caillon and co-authors (to whom it was directly attributed), but which appeared nowhere within the paper. This graph was presented in support of the argument that rises in the atmospheric concentration of carbon dioxide are the result of, rather than the cause of, increases in temperature. However, Caillon and his co-authors concluded in their paper that “the situation at Termination III differs from the recent anthropogenic CO2 increase”, noting that “the recent CO2 increase has clearly been imposed first”.
In fact, the paper suggested that a fluctuation in the Earth’s orbit 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 (the volume of carbon dioxide dissolved in sea water decreases with increasing temperature). It 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. The paper stated that the sequence of events during Termination III is “still in full agreement with the idea that CO2 plays, through its greenhouse effect, a key role in amplifying the initial orbital forcing”.
A paper by Urs Siegenthaler and co-authors, published in the journal ‘Science’ in 2005, described evidence from the Dome C Antarctic ice core for lags of 800, 1600 and 2800 years between deglaciations at terminations V to VII and rises in the atmospheric concentration of carbon dioxide, respectively. However, the programme failed to point out that the record of temperature increases followed by rises in carbon dioxide concentration, which are described in the papers by Caillon and co-authors and Siegenthaler and co-authors, all relate to episodes of deglaciation. The last deglaciation on Earth occurred 12,000 years ago, but the current rise in carbon dioxide and other greenhouse gases, such as methane and nitrous oxide, started during the Industrial Revolution in the 18th century ie more than 11,000 years after the last deglaciation.
Furthermore, the programme failed to point out that the rise in temperature and carbon dioxide levels during Termination III occurred over a period of about 5000 years, much longer than the period since the start of the recent rises in temperature and gas concentrations in the 18th century. It also failed to acknowledge the findings of the paper by Siegenthaler and co-authors that “the atmospheric concentration of CO2 did not exceed 300 ppmv [parts per million by volume] for the last 650,000 years before the preindustrial era”. As the IPCC Third Assessment Report in 2001 pointed out, the scientific evidence shows that the atmospheric concentration of carbon dioxide prior to the Industrial Revolution was 280+/-10 parts per million, and has risen continuously ever since, reaching 377 parts per million in 2006 ie the atmospheric concentration of carbon dioxide has risen in the last 250 years to a level today that is 25 per cent higher than the maximum recorded during a period of at least 650,000 years before the Industrial Revolution.
The programme clearly misrepresented the conclusions of the paper by Caillon and his co-authors, as well as the evidence that the recent increase in global average temperature is following a rise in the atmospheric concentrations of greenhouse gases.
Claim: The oceans expel large volumes of carbon dioxide when they warm, so emissions of greenhouse gases from human activities cannot be responsible for the rise in global average temperature.
Misrepresentation: To support this claim, the programme used clips of an interview with Carl Wunsch, Professor of Oceanography at Massachusetts Institute of Technology. The clips appeared to show Professor Wunsch supporting the claim that sea water contains a lot of dissolved carbon dioxide, which is released when the oceans warm, and therefore supposedly backing the proposition that emissions of greenhouse gases from human activities must be unimportant by comparison.
On 15 March, ‘The Independent’ newspaper published an article by Professor Wunsch, indicating that his views were misrepresented in the programme, which he described as “one-sided, anti-educational and misleading”. The article states:
“In the part of The Great Climate Change Swindle where I am describing the fact that the ocean tends to expel carbon dioxide where it is warm, and to absorb it where it is cold, my intent was to explain that warming the ocean could be dangerous – because it is such a gigantic reservoir of carbon. By its placement in the film, it appears that I am saying that since carbon dioxide exists in the ocean in such large quantities, human influence must not be very important – diametrically opposite to the point I was making – which is that global warming is both real and threatening.”
It is clear that Professor Wunsch considers that the programme misrepresented his views about the effect of greenhouse gas emissions from human activities.
Claim: The variation in global average temperature over the last couple of centuries
can be explained by the effect of solar activity instead of the rise in greenhouse gas concentrations since the Industrial Revolution.
Misrepresentation: The programme presented a graph, attributed to “Svensmark and Christensen”, purporting to show variations in temperature (scaled against unspecified units of temperature change) and solar activity (in unspecified units) for “100 Years”. The record of temperature on the graph extended from 1860 to about 1982, while solar activity covered the range from 1860 to about 1975. The plot of temperature on this graph differed from other records of temperature shown in the programme.
Despite the attribution, the provenance of this graph is not clear – it does not correspond, for instance, to any figures from a paper by Henrik Svensmark and Eigil Friis-Christensen published in the ‘Journal of Atmospheric and Solar-Terrestrial Physics’ in 1997. It does, however, bear a very close correspondence to Figure 2 of a paper by Knud Lassen and Eigil Friis-Christensen published in the ‘Journal of Atmospheric and Terrestrial Physics’ in 1995. This figure plotted the “[e]leven-year running mean of the annual average northern hemisphere land air temperature…relative to the average temperature 1951-1980” against “the filtered length of the sunspot-cycle” (on an inverse scale). The paper claimed that the figure was based on data reported in a paper published by the same authors in the journal ‘Science’ in 1991, and showed that “the variation of the global temperature, particularly the northern hemisphere land air temperature, has been found to be closely associated with the long-term variation of solar activity during the entire interval of systematic temperature measurements from 1851 to 1987”. The authors suggested that the length of the solar cycle “appears to be a possible indicator of long-term changes in the total energy output of the Sun”.
However, 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 programme acutely misrepresented the current state of knowledge about the impact of solar activity on global average temperature.
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