Andrew Turnbull’s recent briefing paper [PDF] for the Global Warming Policy Foundation,The Real Inconvenient Truth or “It Ain’t Necessarily So” has made a small splash in the press this week.
Timed to coincide with the government decision on the Committee on Climate Change’s carbon budget recommendations, Turnbull himself summarised the paper on the pages of the Telegraph, and James Delingpole lauded it in a blog for the same paper.
The 15 page briefing paper discusses the IPCC’s assessment of climate science and the UK policy response. In the Foreword, Lord Lawson praises Turnbull’s work as a ‘dispassionate but devastating critique’, and a ‘measured verdict’.
But how reliable are its conclusions? Sadly, they are not reliable at all. Below are a few examples of where Turnbull gets things badly wrong, and one example of questionable quotation.
â?¢ The “Hockey Stick”
On the IPCC’s assessment of historical temperatures, Turnbull writes that “[i]n its Third Assessment (2003), the IPCC compared its view to an ice hockey stick.”
In fact, though the graph that has come to be known as the “hockey stick” – because of its largely flat shape, with an upward curve at one end – was included, a search of the IPCC website reveals that the words “hockey stick” feature nowhere in the Third Assessment Report. The Report was also published in 2001 – not, as Turnbull states, 2003.
â?¢ Historic variability of temperature
Turnbull writes that:
“Many scientists believe that in the IPCC’s later reports the [temperature] fluctuations in the past 1000 years have been wrongly flattened out, underplaying a Medieval Warm Period (1000 -1350 AD), followed by a Little Ice Age (1550-1850), and the recovery from it over the last 150 years. This alternative view indicates that our climate has been variable long before the recent movements in CO2.”
Later, he writes that:
“tracing the history back over millennia … [e]fforts are made to splice together records of proxies such as ice cores, tree rings, ocean sediments and also social history. But the statistical manipulations of the data required make it possible to achieve almost any result.”
Still later, he writes:
“We need to acknowledge that there have always been fluctuations in our climate. Rather that writing natural forces out of the script, we need to build them into the analysis.”
However, there is no “flatten[ing] out” or “splic[ing]” in the IPCC’s most recent (2007) report: rather, the multiple lines of evidence from temperature reconstructions are laid out side-by-side. It is also clearly not “possible to achieve almost any result” from this data: they represent a range of possibilities, with clear upper and lower bounds.
The section in which they feature is a discussion of ” Northern Hemisphere Temperature Variability” over the past 2,000 years – which explicitly notes “the underlying variability of climate”. Elsewhere, the IPCC notes that temperatures over the past 1,000 years are “punctuated by substantial shorter-term variability”.
Far from being subversive, the “alternative view” Turnbull proposes is taken for granted by the IPCC and reflected throughout their work.
â?¢ A conspiracy to cover up the Medieval Warm Period?
A simple graph showing a ‘medieval warm period appeared in the IPCC’s First Assessment Report in 1990, but was revised in subsequent reports to incorporate more recent research findings. Turnbull proposes a particular theory to explain this revision:
“Early reports from the IPCC acknowledged these fluctuations but, of course, they are inconvenient to the AGW [man-made global warming] believers, one of whom e-mailed another saying “We must get rid of the Medieval Warm Period.” Writing the MWP out of the script made it easier to claim that present temperature levels were unprecedented.”
A search of the CRU emails for the phrase “we must get rid” turns up no results. In fact the phrase is a misquotation of one used by David Deming, a noted climate sceptic, anti-environmentalist and member of the National Center for Policy Analysis – a right-wing libertarian US think-tank which has received funding from the oil company ExxonMobil and Koch Industries.
In 2006 Deming told the US Senate Committee on Environment and Public Works he had “received an astonishing email from a major researcher in the area of â??â??climate change. He said, “We have to get rid of the Medieval Warm Period.”” The email Deming purported to have received was never made public. Turnbull’s quotation, then, is unsubstantiated, misquoted and comes from a source entirely different from the one he claims for it.
â?¢ The scientific consensus
Turnbull constantly challenges the idea that there is a consensus that recent warming is man-made. He writes that: “[t]here is huge controversy about the relative contribution of man-made CO2 versus natural forces”, for instance – and that “[w]hat is frequently described as a “consensus” is no such thing.” Yet a 2004 study of peer-reviewed journal articles found none contesting the consensus position. Another, more recent (2009) peer-reviewed study asked scientific experts the question: “Do you think human activity is a significant contributing factor in changing mean global temperatures?” As it concluded:
“It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes. The challenge, rather, appears to be how to effectively communicate this fact to policy makers and to a public that continues to mistakenly perceive debate among scientists.”
â?¢ Taking natural factors into account
“If CO2 were as important as many AGW theorists claim, why has temperature not followed a steady upward path? Immediately it becomes obvious that the increases of CO2 and of temperature are poorly correlated and that one needs to bring other factors into the story such as the sun, clouds and the way heat is stored in, and distributed around the oceans.”
CO2 and temperature would only have “followed a steady upward path” if they were the only factors affecting climate. But – perhaps unsurprisingly – climate scientists have not failed to notice that the sun warms the earth, or that the sun’s output varies. The IPCC notes, for instance, that “[t]he natural external factors that affect climate include … variations in solar output”; and that “[t]he ocean has an important role in climate variability and change”.
The idea that climate scientists “[need] to bring other factors into the story” is simply false: these factors are already an integral part of the story. As the IPCC demonstrates, models that take into account only natural influences cannot explain the warming observed over the course of the 20th Century: only those that include both man-made and natural influences are able to do so.
â?¢ The mid-century decline in temperatures
Turnbull writes that in the last 150 years:
“unlike the rise in CO2 which has been pretty steady … Temperature rose rapidly from 1900-1940 when the CO2 increase was modest, followed by a small drop in temperature between 1940-70 despite CO2 growth being particularly strong at this time. Between 1970 and the late 1990s both CO2 and temperature increased strongly together. â?¦ If CO2 were as important as many AGW [man-made global warming] theorists claim, why has temperature not followed a steady upward path?”
This argument was one of those used by Martin Durkin in his Channel Four film “The Great Global Warming Swindle” – widely criticised by climate scientists, including in a comprehensive rebuttal submitted to Ofcom. However, a more sophisticated view of the factors affecting temperature rise over the twentieth century provides a clearer picture which does not challenge the importance of CO2 in relation to rising temperatures.
The post-1940 decline in temperatures appears to be linked to increasing emissions of atmospheric aerosols – another man-made pollutant emitted alongside greenhouse gases – which serve to “mask” the latter’s warming effect. When Europe and the US clamped down on aerosol emissions, temperature rise resumed.
The 1940-70 dip was also sharpened by a change in the methods used to collect and measure oceanic temperature samples after 1945. During the second world war, US ships measured the temperatures of the seawater used to cool their engines – which tended to result in higher temperature readings. UK ships resumed this task after the war – but collected samples in uninsulated buckets, tending to give lower temperature readings.
Hence a more detailed view both helps explain temperature patterns between 1940 and 1970, and confirms the importance of CO2 as a driver of temperature rise over the past century.
â?¢ Water vapour, clouds and feedbacks
In his discussion of the effects of clouds on climate, Turnbull states that:
“A hotter atmosphere will hold more water vapour. But does this automatically mean that there will be a positive, i.e. amplifying, feedback effect? Not necessarily. Low level cloud does have an insulating property but high-level cloud also has what is known as an albedo effect, reflecting the sun back into space, which is why cloudy days are cooler. The IPCC models have assumed but not proven a strongly positive, i.e. amplifying, feedback, but have ignored the possibility of negative feedbacks. Some scientists such as Professor Lindzen of MIT argue that the net effect could go either way.”
The IPCC has not “ignored” this possibility – as a search of the IPCC website reveals, they repeatedly reference Richard Lindzen’s writings on water vapour, clouds and feedbacks. (However, it’s worth noting that Lindzen is a marginal figure within the field of climate science who diverges from the scientific consensus on climate change.)
The IPCC also note that “[i]n response to global warming, the cooling effect of clouds on climate might be enhanced or weakened â?¦ Therefore, cloud feedbacks remain the largest source of uncertainty in climate sensitivity estimates” – explicitly discussing the possibility Turnbull claims they have “ignored”.
Water vapour and clouds are not synonymous, however – and, as the IPCC concludes, the weight of available evidence strongly supports the idea that water vapour will reinforce global warming:
“Significant progress has been made since the TAR [Third Assessment Report, 2001] in understanding and evaluating water vapour and lapse rate feedbacks â?¦ New tests have been applied to GCMs [global climate models], and … [n]ew evidence from both observations and models has reinforced the conventional view … Taken together, the evidence strongly favours a combined water vapour-lapse rate feedback of around the strength found in global climate models.”
â?¢ The opinion of David Whitehouse
At another point, Turnbull cites the words of “David Whitehouse, the former BBC Science Correspondent”:
“How many times have you seen, read or heard some climate “expert” or other say that mankind’s greenhouse gas emissions are largely responsible for the unprecedented warming we have seen over the past century, and especially over the past 30 years. It is as if, to some, nature has stepped back, leaving mankind to take over the climate. In reality, whatever one’s predictions for the future, such claims are gross exaggerations and misrepresentations. Natural and human climate influences mingle and even today the natural effects dominate.”
Lord Turnbull does not mention in the text that David Whitehouse is currently the Global Warming Policy Foundation’s Science Editor, and hence that this is a case of a Global Warming Policy Foundation report citing its own staff as experts, without making clear their affiliation.
Whitehouse’s material has also been repeatedly challenged. Bob Ward of the LSE’s Grantham Research Institute on Climate Change and the Environment, for instance, recently criticised a GWPF webpage authored by Whitehouse for “containing 90 errors and misleading statements”.
As we have already seen, both natural and man-made effects are taken into account by climate scientists, who have reached a consensus that the warming over the last century is dominated by the latter. There is little reason to disregard their opinion in favour of that of David Whitehouse.
Nevertheless, even Whitehouse himself accepted in 2007 that: “My own view on the theory that greenhouse gases are driving climate change is that it is a good working hypothesis”.
This last paragraph of this blog was amended on 10June in response to a comment from David Whitehouse. It originally stated that Dr Whitehouse was ‘recently forced to concede’ that greenhouse gases are driving climate change.