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Government scientist's warning on Lord Lawson's climate claims

• 28 Mar 2011, 14:00
• Christian

Lord Lawson invited the chief scientific advisor to the government, Sir John Beddington, to analyse his first book on climate change, An Appeal to Reason: A Cool Look at Global Warming. Beddington was able to identify 20 significant scientific errors in the first section of the title.

An exchange of letters between the two men was released following a Freedom of Information Request. Here, Carbon Brief has identified the key claims in Lawson's book and letters and matched them with Beddington's critique. 

Beddington writes to Lawson [PDF] on 22nd April 2010 after the two men met in May and states that the peer in his book makes "a number of points related to the underlying science of climate change that are incorrect or presented in a misleading way". 

Lawson responds [PDF] on the 25th and accuses Beddington of using the phrase "potentially catastrophic" climate change "without evidence or quantification".

Lawson writes again on the 7th June the same year saying he is "surprised and concerned" [PDF] that the Guardian has run a story stating Beddington has dismissed as "unreasonable" claims by the Global Warming Policy Foundation.

The Guardian had understood the chief scientific advisor to the government to have issued "a veiled attack on the former Tory chancellor and arch climate sceptic Lord Lawson".

Beddington responds [PDF] by saying it was clear from The Guardian story that he had made no direct reference to the Global Warming Policy Foundation and he could "see no merit in writing to the editor of the Guardian as you request." He promises to get back within a week to respond to Lawson's scientific points. 

Finally, Beddington responds on the 22nd of June by launching into a continued discussion about climate science in which he rebuts many of the claims made by Lawson [PDF] in great detail with reference to the scientific literature.

Lord (Nigel) Lawson: There has, in fact, been no further global warming since the turn of the century, although of course we are still seeing the consequences of the 20th century warming.

Sir John Beddington: Short-term temperature trends are meaningless in the context of global warming… In order to see the effects of greenhouse gases, it is necessary to examine the long-term trend, which has clearly been upward (global average temperatures are now about 0.75°C warmer than they were 100 years ago, and the last decade has been the hottest since records began).

NL: The essence of your point seems to be the assumption that, while the temperature record over 20 years (from 1980 to 2000) is immensely significant, the temperature record over 10 years (the first decade of the 21^st century) is of no significance at all. I know of no scientific basis for this seemingly arbitrary distinction.

JB: Your representation of my argument does not accurately reflect what I wrote. The point I was making is that in order to assess the impact of greenhouse gases on global temperature, it is necessary to consider the long-term (multi-decadal) trend…. When we consider the record decade by decade…it is clear that even allowing for uncertainties in the observations, that last three decades have each been significantly warmer than the previous one ie the error bars do not overlap.

NL: The 21^st century standstill (to date [2009])… is something that the conventional wisdom, and the computer models on which it relies, completely failed to predict.

JB: It remains very difficult…to predict year to year changes caused by short-term, internal processes in the climate system such as ENSO - primarily because the climate system is chaotic. [Footnote: It is worth noting that models do indicate that the warming due to increases in greenhouse gases will not be smooth from year to year but will vary, including occasional periods of cooling, even if it is not possible to predict exactly when such periods of cooling will occur.]

NL: Global average temperature was higher in 1998 than during any year between 2001 and 2007.

JB: It is meaningless to compare global average temperature in any two years within a period of a decade or two, because natural climate variability can cause temperatures to fluctuate … 1998 was an unusually warm year, largely due to a natural climate phenomenon known as an El Niño event..

NL: The 21^st century temperature standstill may be due to a marked observed decline in solar activity.

JB: There is no correlation between solar activity and the strong warming over this period.

NL: Calculating the average global temperature is not as straightforward as it might appear at first sight. There are two problems: the first is how best to calculate the global average from the mass of data from individual weather stations around the world; the second is the reliability of the data, in particular that from much of the developing world and the former Soviet Union.

JB: Scientists who calculate global average temperature from these measurements are well aware of the issues involved in doing so, including incomplete coverage and the fact that some temperature measurements are less accurate than others… Furthermore, the evidence that the world is warming does not rest solely on the robustness or otherwise of the direct temperature record. Warming can be seen in a range of other variables: the extent of summer minimum Arctic sea ice has decreased by 0.6 million km² each decade since the 1970s, spring now arrives on average about ten days earlier in the UK than it did in the early 1970s, and global sea level has increased by about 10 cm in the last 50 years.

NL: I am baffled why you should apparently feel that referring to carefully selected phenomena such as the extent of sea ice or the advent of Spring in the UK proves anything at all about either the extent of any warming that has occurred or its probable cause. The temperature is the temperature.

JB: My point in mentioning the decline in Arctic summer sea ice extent and the earlier arrival of Spring in the UK was simply to highlight evidence that confirm that the world is warming. The phenomena are not carefully selected but are part of an increasingly comprehensive body of evidence that shows that our climate is changing that are consistent with AGW….

NL: The US temperature history produced by NASA (and recently revised to correct computer errors) clearly shows both the mid-20th century cooling and the warming that occurred during the last quarter of the 20th century. But the cooling appears much more pronounced than that shown in the Hadley Centre's northern hemisphere chart. For the United States, only three of the last twelve years emerge as among the warmest since records began; and the warmest year of all was 1934.

JB: Global warming is not expected to be spatially uniform because the atmosphere and the oceans redistribute heat around the world… The U.S. comprises less than 2% of the surface area of the globe, so temperatures in this region are not representative of the Northern Hemisphere as a whole.

NL: It is settled science that urbanization raises near-surface temperatures…There are two problems that arise from this. The first is the obvious question of how much of the recorded global warming has in fact been caused by this process…The second, and probably greater problem, is the extent to which the recorder rise in surface temperatures in the late 20th century has been exaggerated by the fact that a large proportion of climate stations are located in cities.

JB: The effect of urban areas on temperature has been examined thoroughly and found to have a negligible effect on the global temperature record.

NL: The significance of urbanisation is still contested.

JB: The significance of urbanisation on the global temperature record are not affected by the urban heat island effect and there are well-established ways of taking the effect into account for those that are… I refer you to my previous response for further information…

NL: Far and away the most important of these [greenhouse] gases - thought to account for at least two-thirds of the greenhouse effect - is water vapour

JB: This in no way undermines the conclusion that human emissions of CO₂ and other greenhouse gases are the main cause of recent warming - for two reasons. First, human activities arenot directly adding significant quantities of water vapour to the atmosphere. Second, the concentration of water vapour in the atmosphere is determined mainly by temperature, with any excess 'raining out' within a few days - so even if human activities were adding more water vapour to the atmosphere, it would not accumulate there…

NL: The more carbon dioxide there is in the atmosphere, the more better the development of plant life on the planet. This is customarily referred to as the 'fertilization effect' of CO₂, and is scarcely a bad thing.

JB: Scientists have shown that increases in productivity caused by this effect will not be universal because other conditions (such as nutrient availability) quickly become limiting. In addition, climate changes caused by increasing CO₂ concentrations are likely to decrease productivity in many regions.

NL: The science of clouds…is one of the least understood aspects of climate science…Most existing climate models employed to predict future temperature levels treat clouds in a way that amplifies the warming effect of carbon dioxide, but this treatment is disputed.

JB: It is true that it is difficult to represent clouds in climate models (although there is no compelling evidence that they introduce a warm bias) and that both the response of clouds to climate change and the associated feedbacks are not fully understood. However, climate modellers are well aware of the uncertainties these issues introduce and factor them into the uncertainties associated with model simulations… The IPCC took these factors into account… the uncertainties certainly don't undermine this conclusion.

NL: While the growth in man-made carbon dioxide emissions, and thus carbon dioxide concentrations in the atmosphere, continued relentlessly during the last century, and continues unabated to this day, the global mean surface temperature, as we have already seen, has increased in fits and starts.

JB: It is true that the trend in CO₂ concentrations over the last century does not exactly match the trend in temperature. But we do not expect it to - mainly because greenhouse gases are not the only determinant of temperature. Factors such as solar activity, volcanic eruptions and human emissions of aerosols also have an effect.

NL: As the Hadley Centre concedes, 'analysis of satellite data shows substantially less warming than at the surface. Climate models predict that we should have seen a relatively greater warming in the troposphere than at the surface; this potential discrepancy between models and observations is not well understood, although uncertainty in observations is the more likely explanation.' Alternatively, the models might just be wrong, or else the data me be recording warming that is not greenhouse related.

JB: The critical point here is that the differences are within the uncertainties of the satellite observations. Uncertainties are particularly large for satellite records…because satellite measurements are affected by non-climate effects such as the body temperature of the instrument and satellite drift in orbit, which need to be accounted for correctly.

NL: It is worth noting the recent acknowledgement by Dr Kevin Trenberth that none of the models used by the IPCC are initialized to the observed state and none of the climate states in the models correspond even remotely to the current climate.

JB: In the article in which this statement appears, the author points out that climate models can provide robust projections of global climate change … However, he also points out that a different modelling technique…can provide more accurate forecasts, particularly over the first few years.  Most modellers agree with this statement and a number of groups are working to develop this method.

NL: The Earth's climate has always been subject to natural variation which has been wholly unrelated to man's activities.

JB:The spatial pattern and trend of recent warming can only be fully explained by human emissions of greenhouse gases.

NL: I do not see how the fact that the first decade of this century has been warmer than any other decade over the past 150 years proves anything at all. There have been other warm periods in the more distant past.

JB: Again, I feel I have been selectively quoted here….It is of course true that there have been warmer periods in the distant past especially if you mean by distant, multi-millenial timescales. Variations in the Earth's orbit around the sun are what have driven those past changes, but the trend since 1750 is estimated at only 0.12Wm-2. These values are an order of magnitude lower than the observed 0.75C warming since pre-industrial times.

NL: If it had not been for a penetrating critique painstakingly developed by two Canadians - Professor Ross McKitrick… and Steve McIntyre…the hockey stick myth would have become the received wisdom, as the IPCC evidently wished it to be… However, in the light of the Canadian critique, two US congressional committees decided to set up two committees of experts… to review the matter. They reported in 2006, and, taken together, their reports wholly vindicated McKitrick and McIntyre's critique. The 'hockey stick'…is now comprehensively discredited.

JB: The methods (particularly the statistical methods that underpin it) and data used to construct the graph have been criticized, and most climate scientists agree that the original graph can be, and has been, improved. However, most scientists also agree that the main conclusion drawn from the graph - that the warming of the late 20th century is unprecedented in the past 1,000 years - is likely to be true.

NL: I am surprised you seek to defend the 'hockey stick'…the statement that it has been improved is disingenuous…The 'hockey stick' which was used by the IPCC to try and demonstrate the effect of man on the temperature of the planet, and which eliminated the Roman warm period, the Little Ice Age and the MWP, has been abandoned and replaced by the very authors who devised it in the first place.

JB: I do not seek to defend the original hockey stick analysis; I am aware that there are issues and uncertainties associated with it. I should also say that my understanding is that there is still much debate over whether the MWP was global in extent and whether it is warmer than today….the validity or otherwise of this graph, and the magnitude and spatial extent of the MWP, do not have any significant bearing on the cause of recent warming or the conclusion that warming will continue if emissions continue unabated.

NL: The amount of warming and its alleged consequences appear to vary geographically too… The fringes of the Greenland ice sheet appear to be melting, while at its centre, the ice is thickening…This diversity makes it all too easy for the likes of Al Gore, as in his tendentious filmAn Inconvenient Truth, to cherry-pick local phenomena which best illustrate their predetermined alarmist global narrative.

JB: Climate change due to greenhouse gases is not expected to be uniform around the world. All the examples presented are consistent with our understanding of how greenhouse gases affect climate.

NL: I am baffled why you should apparently feel that referring to carefully selected phenomena such as the extent of sea ice or the advent of Spring in the UK proves anything at all about either the extent of any warming that has occurred or its probable cause. The temperature is the temperature.

JB: The phenomena are not carefully selected but are part of an increasingly comprehensive body of evidence that shows that our climate is changing that are consistent with AGW…These include the systemic increase in heat content of the top few hundred metres of the ocean…and the rise in global sea level…as well as changes in atmospheric moisture content, global and regional patterns of precipitation changes, and increases in ocean salinity at low latitudes in the Atlantic Ocean.

NL: Sea levels have, in fact, been rising very gradually for as long as records exist, and there is little sign of any acceleration so far. Indeed, the most recent study suggests that the average annual rise amt have been slightly less in the second half of the 20^th century than in the first half… Despite this, particular concern has been widely expressed for the fate of those who live in low-lying island states such as the Maldives in the Indian Ocean, and the small Polynesian islands (such as Tuvalu) in the South Pacific. In fact, studies have shown that the sea level in the Maldives has, if anything, been falling over the last thirty years.

JB: In contrast to the assertions made, the best available records of global sea level change indicate that the rate of sea level rise accelerated between the late 19^th century (when reliable records began) and the late 20^th century ….A recent study by Church et al. (2006) estimated sea level rise at Tuvalu to be 2.0±1.7mm/yr from the two available records starting in 1977 and 1993.

NL: Natural disasters such as hurricanes, monsoons, droughts, earthquakes, tsunamis, and even pandemics (the vogue word for what used to be known as plagues) have always occurred, and no doubt always will; to attribute them to global warming is not science but political propaganda.

JB: Mainstream scientists do not claim that these changes are likely to occur, at least over the next hundred years or so…. Importantly, however, the [IPCC] report also concluded that the likelihood of such 'low probability, high impact' events occurring increases as temperatures rise.

NL: So far as the Greenland ice sheet is concerned, there is no evidence that melting, or rather, net ice loss, is occurring to any significant extent.

JB: There is strong evidence that the Greenland Ice Sheet has decreased in size over the last 10-15 years, with thickening in central regions due to increased snowfall more than offset by increased melting in coastal regions…Temperatures in the high Arctic are indeed thought to have been similar to today in the 1930s, but this in no way undermines the conclusion that recent changes are due to greenhouse gas emissions… There is considerable uncertainty about recent changes in the total size of the Antarctic ice sheet…we would not expect the size of the Antarctic Ice Sheet to have decreased significantly, partly because atmospheric circulation around the continent prevents warmer air from reaching it.

NL: It is understandable that any scientists, especially those engaged in advising governments, should tend to emphasize what they know or believe they know, notably the nature of the greenhouse effect, at the expense of what they do not know. But neither the scientists nor politicians serve either the truth or the people by pretending to know more than they do. It is clearly illegitimate to assume that what is not at present known cannot exist. Uncertainty is uncertainty.

JB: You are, of course, absolutely right to point out that there are uncertainties in climate projections. However, a critical point is that these uncertainties relate predominantly to the detailed spatial and temporal changes that we can expect. The basic conclusions that greenhouse gases cause warming, that the average global temperature is rising linked to increases in greenhouse gases from human activities and that this trend can be expected to continue is based on well-established scientific principles and wide-ranging evidence.