The Intelligent Voter’s Guide to Global Warming (Part I)

Part II is published in April Quadrant. Subscribe now…

In a news story on March 20, 2000, “Snow falls are now just a thing of the past”, the UK’s Independent newspaper reported:   

Sledges, snowmen, snowballs … are all a rapidly diminishing part of Britain’s culture, as warmer winters—which scientists are attributing to global climate change—produce not only fewer white Christmases, but fewer white Januaries and Februaries … According to Dr David Viner, a senior research scientist at the climatic research unit (CRU) of the University of East Anglia, within a few years winter snowfall will become “a very rare and exciting event … Children just aren’t going to know what snow is”.

This millenarian prediction from the world’s most prominent climate research centre was a dud. When the news story appeared ten years ago, an unanticipated pause in global warming was already taking place, and global warming has not resumed since then. On January 7, 2010, a NASA satellite photographed the UK covered entirely by a blanket of snow. The published photograph shows the familiar shape of the map of England, Scotland and Wales, frozen white, and set in an ocean of dark blue silk, with the edges partly obscured by wisps of cloud. In the winter just ending, Britain underwent yet another winter of heavy snowfalls. On November 29 the Independent had a story headed, “Cold comfort for a Britain stuck in a deep freeze”. 

With Julia Gillard’s sudden switch to support for a carbon price, Australia in 2013 could be the first country to hold an election with anthropogenic global warming (AGW) as the pivotal issue. If Tony Abbott is still Opposition Leader he will see an emissions trading scheme (ETS), or carbon tax, as a target that is as vulnerable as John Hewson’s GST proposal in 1993. At that time Abbott was Hewson’s press secretary, and Hewson was “cooked slowly” by Paul Keating in a protracted election campaign. 

We have written this piece as an intelligent voter’s guide to global warming—to provide basic information often missing from the debate. In Part 1 we examine the science, and in Part 2 the practicalities of an ETS and carbon tax, and the politics. All three aspects—science, economics and the associated politics—intersect and drive each other.  

I. The science 

Man-made emissions are likely to cause a doubling of atmospheric carbon dioxide during this century and this increase will continue to have a warming effect on global temperatures. One of the disappointing distortions of the climate science debate is the claim that sceptics deny this relationship. What sceptics are sceptical about is the strength of this AGW effect. A strong AGW effect would be an increase in global average temperatures of 2.5 to 4 degrees or more, with potentially disruptive outcomes, such as a possible large rise in sea levels. A weak AGW effect would be an increase of 1 degree or less, a number of much less concern. 

One of the constants of climate, like that day-to-day local phenomenon the weather, is its variability. We are living during a warmer period known as an interglacial, which began about 11,400 years ago. It is an “interglacial” because for the previous 2.5 million years, much of northern Eurasia and North America has been blanketed by kilometres-deep ice sheets. This ice age or glacial has been interrupted by warmer interglacials of from 10,000 to 20,000 years occurring at intervals of about 100,000 years. 

These transitions—into and out of an ice age—are triggered by various, overlapping Croll–Milankovich cycles which change how much solar radiation our planet receives, and where. Croll–Milankovich cycles are due mainly to interactions with the gravitational fields of other planets, and shift the Earth’s orientation and orbit around the sun and can be precisely calculated backwards and forwards through time. The start of our interglacial was dramatic and occurred over a human lifetime. 

The eccentricity of the Earth’s orbit is currently small and decreasing. This will continue for 30,000 years, which means that our current interglacial is likely to be exceptionally prolonged. By some lucky happenstance our civilisation sits in an astronomical sweet spot, and we probably have hundreds of generations to prepare for the likely return of an ice age. 

Average temperatures during an interglacial are stabler than during a glacial. But over the last 5000 years there have been climatic changes severe enough to have disrupted a number of agrarian societies. As well as the Croll–Milankovitch cycles, there are variations in the output and nature of radiation from the sun itself. A solar cycle of about eleven years manifests itself visibly by sunspots. As the cycle reaches its maximum, sunspots become more frequent, and total solar irradiance increases slightly. 

This difference in total solar output (only about 0.1 per cent) is regarded as insufficient in itself to cause climate changes of any significance. However, the sun’s short-wave radiation (from the ultraviolet through to x-rays) varies greatly and has significant effects on the earth’s stratosphere, the layer of air about ten to fifty kilometres above the Earth’s surface in temperate latitudes. 

There is also a “solar wind” (a stream of charged particles), whose variable intensity may predict the intensity of the next solar cycle. The solar wind causes the spectacular displays of lights known as auroras and protects Earth’s atmosphere from cosmic rays from outside the solar system. It is argued controversially that cosmic rays (they are in fact particles, not rays), may trigger cloud formation and affect climate. Over the last 10,000 years, changes in solar activity and the nature of solar radiation (but not changes in total solar output) have most likely had significant climatic effects.

There was a Little Ice Age, from about 1300 until about 1850, typified by the freezing of the River Thames and a decline in European agriculture. This 550-year span is associated with three periods of low sunspot activity, known as minima. During these low sunspot periods, the solar wind is also less active, fewer auroras are observed and cosmic rays from outside the solar system cause the formation of carbon-14 in the atmosphere; this is detected in tree rings (as trees inhale carbon dioxide). Conversely, periods of high solar activity result in reduced carbon-14 levels in tree rings. Brian Fagan, an archaeologist, writes that tree rings show: 

a well-defined fall in 14C levels and a peak in solar activity between about AD 1100 and 1250, the height of Europe’s Medieval Warm Period … There is certainly a nearly perfect coincidence between major fluctuations in global temperature over the last 1000 years and the changes in 14C levels identified in tree rings. This implies that long-term changes in solar radiation may have had a profound effect on terrestrial climate over decades, even centuries.

There was an immediate temperature spike when the current interglacial began 11,400 years ago. Average temperatures at many sites from 8000 to 10,000 years ago were about 2 degrees warmer than now. Since then global average temperatures have gradually declined, with peaks and troughs, and variations from site to site. A central Greenland ice core shows a Minoan warming about 3500 years ago, a Roman warming about 2000 years ago, the Medieval Warm Period, and the twentieth-century warming, with each new warming being about 1 degree cooler than its predecessor. Richard B. Alley, who worked on this ice core, commented: “the best paleothermometers are probably those on the ice sheets”. 

Ice cores, when available, are perhaps the best evidence of temperatures in the past, because the isotopic composition of a section from an ice core reflects just one main influence. This is the temperature of the air from which it condensed, as heavier molecules of water vapour (with more neutrons) are the first to condense when air chills. Climate scientists who argue for a strong AGW effect have tended to rely on less reliable proxy evidence such as tree rings (which may reflect a number of influences, for example the availability of such key nutrients as water) when claiming that recent temperatures are “hotter than ever”. 

The pre-industrial level of atmospheric carbon dioxide was about 280 parts per million volume (ppmv). In the late 1940s this began a steady rise to the current level of about 390 ppmv. The steady graph of this year-by-year rise, with a small seasonal wobble as northern hemisphere plants inhale carbon dioxide in spring and summer, points to a single dominant cause—man-made emissions. To the extent that this is causing a greenhouse effect humans are responsible.

Carbon dioxide is transparent to most incoming solar radiation. But it is opaque to certain wavelengths of infrared or “black body” radiation and blocks the escape of this radiation into space from the sun-warmed surface of our planet. Hence the greenhouse effect. In the absence of positive or negative feedbacks, the doubling of atmospheric carbon dioxide would eventually raise global average temperatures by about 1 degree. The main qualifiers here are “eventually” and the role of feedbacks.

A majority of Western climate scientists, in predicting severe global warming, argue that there are positive feedbacks causing a strong AGW effect. As increased levels of carbon dioxide heat the atmosphere, atmospheric water vapour (humidity) increases. This water vapour is also a greenhouse gas, and is already far more plentiful than carbon dioxide. Increasing it will amplify the warming caused by increased carbon dioxide—perhaps by up to 5 degrees or more for a doubling of carbon dioxide, according to some general circulation models relied upon by the United Nations Intergovernmental Panel on Climate Change (IPCC).

However, other climate scientists argue that the feedbacks can be negative, so there is only a weak AGW effect. The relationship between a warming atmosphere and increased water vapour is complex. Increased water vapour will eventually condense, warming the air around it, as latent heat is released by the change from a gaseous to a liquid state. The condensed vapour may become low-level cloud, which has a cooling effect (as it reflects incoming radiation), or high-level cirrus cloud, which has an overall greenhouse effect. 

Data from weather balloons (radio-sondes) suggest that with increased warmth at the planet’s surface, there may be less water vapour in the atmosphere above about three kilometres, where a positive feedback from water vapour might occur. It is also argued that high-level cirrus cloud cover, which blocks escaping radiation, decreases over tropical oceans as temperature increases. The IPCC’s Fourth Assessment Report of 2007 acknowledges: “Cloud feedbacks remain the largest source of uncertainty.”

The second qualifier about a doubling of carbon dioxide raising global temperatures is 1 degree “eventually”. The oceans and atmosphere have been described as unequal dancing partners, with the atmosphere reacting quickly and the oceans heavy-footed, slow and out of step. 

Radiative or climate forcing is the net change in incoming and outgoing radiation energy in the climate. It is measured in watts per square metre. There is a positive forcing if, for example, an increase in greenhouse gases blocks outgoing radiation, and there is a negative forcing if, for example, reduced sunlight enters the Earth’s atmosphere as its orbit becomes more eccentric. 

Oceans have about 200 times the mass of the atmosphere. They may take some hundreds of years to respond fully to an increase in radiative forcing (typically extra sunlight determined by a Croll–Milankovich cycle). Among nine errors found by a British court, Al Gore’s movie An Inconvenient Truth erroneously assumed that carbon dioxide levels and temperature rose and fell simultaneously—there was an “exact fit”. This was referred to as “Error 3” in the proceedings, which were initiated by a school governor (a lorry driver) against the educational authorities. 

The Al Gore movie implied that carbon dioxide levels were somehow driving temperature. At about the time the movie was made, clear evidence emerged that carbon dioxide levels rise and fall several hundreds of years after a rise or fall in temperature. Carbon dioxide changes lag behind temperature changes. Historically, carbon dioxide has not been the significant driver of temperature that was once assumed. The erroneous assumption of an “exact fit” between carbon dioxide and temperature has contributed greatly to the present popular misunderstandings surrounding AGW. 

There are various explanations for this lag. Warming water has a reduced ability to retain carbon dioxide and as the oceans slowly warm or cool they may release (or absorb) carbon dioxide. Temperature-induced changes in biological activity, rainfall or the weathering of rocks also play a role.

It is surprising that the ocean depths respond at all to changes in radiative forcing. Compared with metals, water is a poor conductor of heat. Intuitively you might expect the warmer, lighter water to sit at the surface and not mix with the colder depths. But there is a slow mixing, as exemplified by the Atlantic’s Gulf Stream. When the Atlantic’s surface is heated at the tropics by sunlight, some water evaporates. The remainder becomes saltier and heads north to colder latitudes, where it chills. This saltier water, as it chills, becomes heavier than the cold water which it overlays. It sinks and mixes with deep currents that head back to the tropics where they upwell again. An enormous conveyor belt is created, warming North Atlantic coastal regions.

The different cycles of these ill-assorted dancing partners, the atmosphere and ocean, contribute to the chaotic behaviour of climate. Several oceanic oscillations have been identified that influence climate. The peak for recent warming, 1998, was the outcome of an exceptional El Niño event in the Pacific. A big El Niño event in 2010 has also caused a recent jump in global average temperatures, which may now be about to subside. The oceans are not well understood. Methods for systematically measuring ocean temperatures, starting in the nineteenth century, have varied and only become reliable in the last five years (with a small, very recent, decline during this time observed in ocean temperatures). The ocean is where any excess heat must theoretically end up, since dry land eventually gives up any received heat while the oceans absorb it; however, recent evidence shows that this is just not happening.

Another puzzle for climate modellers is that global average temperatures have not kept up with the steady rise in atmospheric carbon dioxide. General circulation models relied on by the IPCC predicted these temperatures would rise in the current decade, but this has not happened. Accurate measurements of atmospheric carbon dioxide began as recently as 1958. The significant recent rise in atmospheric carbon dioxide began in about 1950. But there was no increase in global average temperatures until about 1976. In fact from 1940 to 1975, a period sometimes called “the Little Cooling”, temperatures appear to have been slightly lower than in the 1930s of dust-bowl fame.

Pro-AGW climate scientists claim the Little Cooling was caused by aerosols, such as sulphur dioxide, produced by the rapid expansion of industry and motorised transport that began in about 1950. According to these scientists, by 1976 there was a reduction in these aerosols because of clean air legislation in Western countries, allowing the warming from extra carbon dioxide to take effect. There are two problems with this explanation. The largely oceanic southern hemisphere, where there are few of these anthropogenic northern hemisphere aerosols, was also subject to the Little Cooling. Also, as aerosols from North Atlantic countries decreased, this may have been matched by an increase in aerosols from the rapid industrialisation of China and India in the late twentieth century. 

The 1980s were warmer than the 1970s, the 1990s were warmer than the 1980s, and the 2000s have been warmer than the 1990s. However, the rise in temperatures starting in 1976 stopped in about 2000. Since then temperatures have flattened out and may have reduced. Although the decade to 2009 has on average been warmer than the average of the previous decade, it has not become warmer than the final years of the last decade, as strong-AGW models predicted. Atmospheric carbon dioxide has been steadily rising from 1950 to the present, but there has been a significant increase in temperature for only twenty-five of those sixty years. 

This increase has been about 0.4 degrees and is broadly equal to the increase from 1860 to 1940, when changes in atmospheric carbon dioxide could not have been an influence. All of this suggests there is not a clear correlation between the rise in atmospheric carbon dioxide over the last sixty years and the recent increase in temperatures. The increase that has occurred, which is only fractions of a degree, is explicable as a natural fluctuation, part of the chaotic dance movements of the climate, although it is likely that there is a small AGW contribution, which is extremely difficult to identify.

The modest increase in temperatures does not fit well with bold predictions of increases of several degrees over the remainder of this century. There is a further problem with these predictions. This is that the greenhouse effect of carbon dioxide increases is logarithmic. It is not linear. Richard Lindzen, a climate scientist who is a professor of meteorology at MIT, has explained: 

In terms of climate forcing, greenhouse gases added to the atmosphere through man’s activities since the late nineteenth century have already produced three-quarters of the radiative forcing that we expect from a doubling of CO2 … the impact of CO2 is nonlinear in the sense that each added unit contributes less than its predecessor. For example, if doubling CO2 from its value in the late nineteenth century—from about 290 parts per million by volume (ppmv) to 580 ppmv—causes a 2 per cent increase in radiative forcing, then to obtain another 2 percent increase in radiative forcing we must increase CO2 by an additional 580 ppmv rather than by another 290 ppmv. At present, the concentration of CO2 is about 380 ppmv. The easiest way to understand this is to consider adding thin layers of paint to a pane of glass. The first layer cuts out much of the light, the next layer cuts out more, but subsequent layers do less and less because the painted pane is already essentially opaque.

Lindzen’s “already produced” radiative forcing should not be confused with the effect of this forcing on global average temperatures, which may take decades or centuries to respond, because of the thermal inertia of the oceans. His conclusion is that if we believe the climate models, “we have long since passed the point where mitigation is a viable strategy”. His estimate of the future outcome is: “Attempts to assess climate sensitivity by direct observation of cloud processes, and other means, point to a conclusion that doubling of CO2 would lead to about 0.5 degrees warming or less.” 

The critical issue in the global warming debate is climate sensitivity. There is general agreement that acting by itself there would be a weak AGW of about 1 degree from a doubling of atmospheric carbon dioxide above pre-industrial levels. If there are positive feedbacks which amplify that effect above 1 degree, the climate is more sensitive, and if there are negative feedbacks that would reduce that warming below 1 degree, the climate is less sensitive. 

One way of estimating sensitivity is to examine past events, where there is a known change in radiative forcing and it is simple to calculate the extra (or fewer) watts per square metre that result from the change and observe the effect on average temperatures to obtain a value for sensitivity. When the Last Glacial Maximum finally ended about 11,400 years ago, there was a large increase in average temperatures relative to the increase in solar radiation reaching the Earth at that time (from a Croll–Milankovich cycle). Supporters of the strong AGW case point to this event as evidence for positive feedbacks and a high value for climate sensitivity. 

Deducing climate sensitivity to radiative forcing from extra sunlight when the Last Glacial Maximum ended and using that number to determine the climate sensitivity to radiative forcing from extra carbon dioxide at the present time, when average temperatures are several degrees warmer, is not straightforward. As well as the initial radiative forcing from extra sunlight at the end of the Last Glacial Maximum, there would be the following forcings induced by the change in solar radiation received by Earth: (1) reduced albedo (reflection of sunlight into space) as ice and snow retreat and dark vegetation advances and rocks and earth are exposed; (2) additional trace greenhouse gases from various sources, in particular methane (a much more potent greenhouse gas than carbon dioxide) released from melting permafrost; and (3) the greenhouse effect of additional water vapour as ice and snow melt. The value of these induced forcings can only be inferred with a high degree of uncertainty. 

A further reason for scepticism is the temperature trend for central Greenland over the last 100,000 years. An ice core shows that during the last 10,000 years average temperatures in central Greenland have varied by no more than about 2 or 3 degrees. But over the previous 90,000 years (the period of the last ice age) there were sixteen sudden fluctuations of about 10 degrees or more (some of almost 20 degrees) with many smaller fluctuations of about 5 degrees. These violent and frequent jumps compared with the current relative stability in central Greenland indicate that climate sensitivity during the 90,000 years of the last glacial may have been much higher than now. There may have been positive feedbacks then that no longer operate when temperatures are warmer.

Climate sensitivity has also been estimated from short-term cooling following recent volcanic eruptions and the global temperature trend in the twentieth century. Some high and low numbers for climate sensitivity have been estimated from recent volcanic eruptions. So this is a contested area. The global temperature trend over the twentieth century may also not provide a convincing basis for determining sensitivity. There are peaks and troughs in the modest warming of about 0.8 degrees occurring since the late nineteenth century, which could have been affected by a variety of poorly understood influences, such as clouds and oceanic oscillations. Add to this the uncertainty about the exact extent of current warming. Land surface temperature measurements tend to be concentrated near cities, which are heat islands. Despite corrections for this effect, there is evidence of “contamination patterns” in regard to land surface records, relied upon by climate scientists, “related to urbanisation and other socioeconomic influences” causing “an overall warm bias over land”. Our current level of understanding is such that studies relying on past events to produce a high (or low) value for climate sensitivity are dartboard science. 

There is also a crucial piece of evidence, publicised by David Evans, suggesting it is unlikely that climate sensitivity is a large number. Evans, an electrical engineer and mathematician, worked for the Australian Greenhouse Office (now the Department of Climate Change) from 1999 to 2005, modelling Australia’s carbon. He became sceptical when, in his view, “the evidence supporting the idea that CO2 emissions were the main cause of global warming reversed itself from 1998 to 2006”. The crucial evidence Evans found is in a 2006 report, Temperature Trends in the Lower Atmosphere by the US government’s Climate Change Science Program (CCSP). Climate modellers had predicted a “hotspot” in the atmosphere, at a height of about twelve kilometres in the tropics, which would prove that climate sensitivity was a high number. This “hotspot” should have emerged over the period of global warming which occurred from the late 1970s until the end of the twentieth century. But many thousands of radiosonde measurements from 1979 to 1999 found it did not. 

Why is this evidence crucial? It is well known that air temperature decreases with altitude, except for rare temperature inversions, until the stratosphere is reached. This reduction in temperature, caused by the reduction in air pressure with increasing altitude, is known as the “lapse rate”. The lapse rate reduces with increases in humidity. The lapse rate would be about 10 degrees per kilometre of altitude if air was perfectly dry and rising quickly. But if air is very humid, it can be as low as 4 degrees per kilometre. 

When global average temperatures were increasing over the period from 1979 to the end of the twentieth century, the extra water vapour generated by these higher temperatures could increase the depth of humid atmosphere. The CCSP’s 2006 report predicted: “the lapse rate can be expected to decrease with warming such that temperature changes aloft exceed those at the surface”. However, the radiosonde measurements confounded this prediction. The report found: “observational data sets show more warming at the surface than in the troposphere [the atmosphere up to about twelve kilometres], while most model runs have larger warming aloft than at the surface.” 

If warming at the surface exceeded warming in the upper troposphere, this probably means the extra humidity was condensing into low-level clouds, which reflected incoming sunlight (with a negative effect on temperature), rather than increasing the depth of humid air that would have a greenhouse effect. Although the CCSP is silent on the matter, the inference is that climate sensitivity is a low number and feedbacks from changes in radiative forcing are negative rather than positive. 

The IPCC’s First Assessment Report in 1990 and Second Assessment Report in 1995 included graphs showing that temperatures were warmer in the Medieval Warm Period from about 1000 to 1300 than they were towards the end of the twentieth century and that there was a Little Ice Age. This was the widely accepted view at that time and confirmed by numerous studies. (It has since been confirmed by Loehle and McCulloch’s 2000-year temperature reconstruction, published in 2008, based on eighteen series of non-tree-ring proxies, which found that the warmest tridecade of the Medieval Warm Period “was warmer than the most recent tridecade, but not significantly so”.)

Then in its Third Assessment Report of 2001, the IPCC dropped graphs which showed a warmer period in medieval times and instead included the now notorious “hockey stick” graph. This new graph purported to show northern hemisphere temperatures from 1000 to the end of the twentieth century, with the Medieval Warm Period and the Little Ice Age as minor fluctuations in a relatively flat line, and a sharp rise only at the end of the twentieth century, resembling the blade of a hockey stick. It supposedly represented a warming in the last two decades of the twentieth century which was unprecedented over the previous 1000 years. 

The hockey stick came from a 1999 study by Michael Mann and co-authors based mainly on studies of growth rings of trees, and also ice cores and coral, which provided proxy evidence of climate over the last 1000 years and built on an earlier study the co-authors published in the influential science journal Nature. In promoting this rewriting of climate history, the IPCC ignored numerous earlier studies and anecdotal historical evidence of the Medieval Warm Period and Little Ice Age. 

The wider climate science community accepted this convenient reversal of a historical paradigm. It required two amateurs to demolish the hockey stick. Stephen McIntyre, living in Toronto, had been a statistician working at the speculative end of the mining industry. He had memories of Vikings in Greenland from his schooldays and became casually interested in the IPCC’s hockey stick.

In April 2003 he was surprised to read an article by an IPCC author, Keith Briffa from the University of East Anglia, finding a decline in growth-ring widths for a large sample of trees in the twentieth century. A decline in growth-ring widths would indicate a decline in temperature. This seemed at variance with the use of tree-ring widths in the IPCC’s hockey stick to show a temperature increase in the twentieth century. McIntyre assumed there was an explanation for this. Out of curiosity he wrote to Mann, the main author of the hockey stick. According to McIntyre: 

To my astonishment, Mann said that he had forgotten where the data were. It seemed that nobody had verified the study in the way that I was used to things being verified [in the mining industry where geologists must make available all data on which their reports are based]. I thought—well, if nobody else has done this, I will.

McIntyre was not an academic. He teamed up with Ross McKitrick, a professor of economics at the University of Guelph, and together they published an analysis of Mann’s hockey stick. They found the data did not produce the results claimed by Mann and his co-authors “due to collation errors, unjustifiable truncation or extrapolation of source data, obsolete data, geographical location errors, incorrect calculation of principal components and other quality control defects”. 

The findings of McIntyre and McKitrick caused a furore. A committee headed by Edward J. Wegman, a professor of statistics and chair of the US National Research Council’s Committee on Applied and Theoretical Statistics, lodged a ninety-two-page report (including appendices) with the US Congress in 2006. The Wegman report found McIntyre and McKitrick’s criticisms of the hockey stick were “valid and their arguments to be compelling”. The report identified a “decentering error” in Mann’s hockey stick findings, caused by selecting the period 1902 to 1995, when temperatures were rising, to calibrate the proxy data set. This was unrepresentative and dissimilar to the millennium temperature profile and “its net effect … is to preferentially choose the so-called hockey stick shapes”. The report suggested Mann and his co-authors may not have been aware of their error and found: “Even though their work has a very significant statistical component … there is no evidence that Dr Mann or any of the other authors in paleoclimatology studies have significant interactions with mainstream statisticians.”

McIntyre and McKitrick found that the hockey stick shape disappeared, using Mann’s data, if a particular bristlecone pine chronology was omitted. This chronology was contained in Graybill and Idso’s 1993 study, “Detecting the Aerial Fertilization Effect of Atmospheric CO2 Enrichment in Tree Ring Chronologies”. The purpose of the study was to test if increases in atmospheric carbon dioxide had a fertilising effect on bristlecone pines, and they did. The tree rings were wider. Arguably a study designed to determine the fertilising effect of carbon dioxide should not have been included in a later survey using tree rings as temperature proxies. Higher carbon dioxide levels rather than warmer temperatures may have been the main influence on the increased rate of growth. Tree rings are problematical temperature proxies because they may be a proxy for rainfall and a variety of influences as well as temperature. 

The outcome was that a historical paradigm—the existence of a distinct Medieval Warm Period and Little Ice Age—was jettisoned on the basis of ambiguous data from some bristlecone pines. This paradigm had been established by more than a hundred studies of which more than twenty related to the southern hemisphere, although it should be emphasised that the southern hemisphere data are not conclusive regarding a Medieval Warm Period. 

The hockey stick was a cause célèbre among a group of interested observers, and its defects were publicised on a website, Climate Audit, which McIntyre now set up. But the deficiencies of the IPCC process did not become known to a wide public until the Climategate e-mails, more than a thousand of them, were leaked or hacked from the website of the University of East Anglia in November 2009. The most notorious of these was an e-mail from Professor Philip Jones to Mann and his co-authors dated November 16, 1999, which stated: “I’ve just completed Mike’s Nature trick [referring to the journal where the hockey stick first appeared] of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) and from 1961 for Keith’s to hide the decline … Cheers Phil.” 

We have already alluded to Keith Briffa’s tree rings anomalously indicating a decline in temperature in the late twentieth century. This e-mail is referring to a graph in the IPCC’s Third Assessment Report showing several coloured lines that converge in the late twentieth century, at which point a green line representing Briffa’s study is amputated, because including it in full would have shown a decline in temperature, implying a credibility problem with the IPCC’s methodology. McIntyre has written regarding this e-mail:

As a reviewer of the [IPCC’s] Fourth Assessment Report I asked that the deleted data be shown and explained as best they could. They refused. Jones’s version of the trick was even more simplistic [than Mann’s]—he simply spliced temperature data onto tree ring data, removing the real data—a technique that Mann later denied had ever been used.

The hockey stick has spawned a number of new hockey sticks. As recently as November 2009 a “news scan” with the reassuring headline “Still Hotter than Ever” in the Scientific American (a sister publication of Nature) affirmed: “A new analysis creates a better ‘hockey stick’ of rising temperatures.” These attempts to resuscitate the hockey stick have been criticised on McIntyre’s Climate Audit website, mainly on the basis that the new hockey sticks essentially recycle the same questionable data—a view which is confirmed in a Climategate e-mail of Briffa’s. McIntyre has continued to find errors in new studies, such as the cherry-picking of data. The relish and banality of the headline “Still Hotter than Ever” and the phrase “better ‘hockey stick’” are symptomatic. They are the language of a climate change industry intent on self-preservation and selling a product.

The original hockey stick should have been buried and forgotten after the Wegman report. What is of greater concern is that a wider community of climate scientists has stood by the authors after errors were exposed, and continues to do so. If the groupthink of climate scientists requires them to defend the pseudoscience of the hockey stick, can their other findings be trusted?

The final part of this article is here…

Geoffrey Lehmann is a poet. He was formerly a partner of a major international accounting firm and Chairman of the Australian Tax Research Foundation.

Peter Farrell is Founder and Executive Chairman of Resmed Inc, foundation Director and former Professor of the Graduate School of Biomedical Engineering at the University of New South Wales, Chair of the Executive Council, Division of Sleep Medicine, Harvard Medical School and Member Visiting Committee, Whitaker College of Life Sciences MIT.

Dick Warburton is Chairman of Westfield Retail Trust, Magellan Flagship Fund Ltd and the Board of Taxation and a Director of Citigroup Pty Ltd and of the Smith Family of which he is also Chairman-elect. He is a former Chairman and CEO of Du Pont Australia and New Zealand. 

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