Select Committee on Science and Technology Appendices to the Minutes of Evidence


Memorandum submitted by the Geological Society of London

  The Geological Society of London, founded in 1807, is the oldest geological society in the world. It has 8,800 members world-wide, and is both a learned society and a professional body.

  This submission was prepared by Professor RCL Wilson (Honorary Secretary, Foreign and External Affairs), with contributions from Dr Stephen Blake (Open University), Professor Geoffrey Boulton FRS (University of Edinburgh), Lord Oxburgh FRS (President elect, and Imperial College), Professor Sir Nicholas Shackleton FRS (University of Cambridge), and Professor Bob Spicer (Open University). These colleagues and members of the Society's External Relations Board have commented on several drafts. The submission has been approved by the Board.

  Changes in atmospheric CO2 and temperature over the last 400,000 years as recorded in the Antarctic Vostok ice core (lower left box), and atmospheric CO2 over the last 1,000 years. The caption for this figure is on page 1.

  The figure shows data obtained from cores obtained by drilling through the Antarctic ice sheet at the Russian Vostok research station1. Variations in temperature above the present day mean of -55.5ºC are shown, based on an analyses of the hydrogen isotopes present in the ice. The plot of atmospheric CO2 content was obtained by analysing bubbles of air trapped in the ice. The small box in the upper right diagram shows the rapid increase in CO2 caused by the industrial revolution (note that this part of the diagram shows a time span of 1,000 years, whereas the main diagram spans 400,000 years).

  The left hand plot in the lower left box shows changes in the amount of solar radiation received at the Earth's surface (insolation) in mid-June at 65º North. Mid-June insolation in northern high latitudes is thought to be the key to the origin of glacial periods. If summers in these areas are cool enough, winter snows will survive, leading to successive annual accumulations of snow and ice. Variations in high northern latitude summer insolation are caused by variations in the shape of the Earth's orbit (eccentricity), the angle of its rotational axis (obliquity) and precessional changes. The increase in insolation that commenced about 20,000 years ago triggered the end of the last glaciation. Insolation in northern high latitudes has now almost returned to the level it was 20,000 years ago, but as yet the climate system has not responded to this change.


  The underlying theme of this submission is that an essential ingredient of the "critical appraisal" referred to in the second aim of the case study is to learn from the past to illuminate the future. The Society has four areas of concern which it hopes the Committee will investigate; these are summarised below:

    I.  The extent to which knowledge and understanding of past changes in climate and atmospheric composition have contributed to the development of scenarios of future change considered by the Government.

    Key aspects of such knowledge and understanding are that geological data:

      —  provides the only information we have about how the Earth's climate system has behaved over meaningful lengths of time (ie hundreds of thousands of years, in contrast to reliable historical records which only extend back about 150 years);

      —  provides a record of changes in atmospheric composition before anthropogenic influences took effect;

      —  shows that the Earth's climate system may flip rapidly (in decades) from a colder to a warmer mode;

      —  shows that sudden releases of carbon into the atmosphere (comparable in size to that being caused by the burning of fossil fuels and other anthropogenic causes) are only removed slowly over tens of thousands of years.

    II.  The extent to which Government ensures that the climate modelling studies used to predict global and regional climate changes are evaluated by testing their ability to replicate past climate changes that occurred in both greenhouse and icehouse worlds.

    The Society's key concerns are:

      —  that climate models have inherent limitations due to their ancestry in models designed to predict the behaviour of today's weather systems, and because they have to simplify an exceedingly complex climate system in which processes operating in the atmosphere, oceans, ice sheets, and solid Earth are linked together;

      —  the models are unable to fully replicate past climates during periods when the Earth was much colder, and much warmer, than it is today. The flaws are most marked in reproducing conditions in continental interiors during greenhouse climates that characterised much of the Earth's history over the last 500 million years;

      —  therefore continued comparison of model simulations with geological data about past climates are required to inform the design of improvements necessary to provide more reliable predictions about future global and regional climate changes forced by rising atmospheric CO2 levels.

    III.  The extent to which Government has addressed the implications of rapid short term changes in weather and climate caused by large volcanic eruptions.

    Historical and geological records show that large eruptions can cause significant cooling at regional and global scales resulting in "volcanic winters" that could have severe agricultural, economic, and political implications.

    IV.  The extent to which Government seeks the views of a broad range of scientists in addition to the advice given by its appointed advisers and consultants.


  1.  It is natural that the institutions directly concerned with current weather and climate should be consulted over climate change. However, reliable climate records go back little more than 150 years—a mere blinking of the eye in the hundreds of millions of years of Earth history. Humanity's activities may well be triggering changes in the present climate, but to understand the extent to which similarly large changes may have occurred in the past without anthropogenic intervention, it is necessary to look at past climate changes as recorded in the geological evidence—especially in the sediments of the deep oceans and in ancient ice sheets. It is not clear that the Government has sufficiently taken advantage of the work of geological specialists in these areas. In the pages which follow we elaborate the contribution that studies of this kind, combined with others, may make to understanding changes in the Earth's climate.

  2.  This submission focuses on the second aim of the case study, namely to identify "what critical appraisal there has been of models predicting climate change, increasing concentrations of carbon dioxide, and other potential drivers". The underlying theme is that an essential ingredient of such "critical appraisal" is to learn from the past in order to illuminate the future. To do this scientists use their understanding of the Earth's climate system to interpret the information they collect from fossil climate indicators (often referred to as proxy climate data).

  3.  Historical records indicate the extent of climate change over the last few centuries, but a pattern of repeated climate change is only revealed by examining the geological record. The mechanism by which the climate system may change can be demonstrated by correlating observed effects preserved in the geological record with postulated causes. Usually this only leads to a qualitative understanding, which does not yield many insights concerning changes in the interconnectivity between different components of the climate system. Palaeoclimatologists obtain a deeper quantitative understanding by using computer generated climate models both to aid their interpretation of proxy climate change data, and to explore the possible effects of changes in different climatic forcing agents. Increasingly geological techniques permit a quantitative record of climatically determined parameters to be reconstructed through time. Although this does not directly indicate the causes of change, correlations between measures which reflect different climatic variables can suggest causality. Palaeoclimatologists can, by using computer generated climate models, attempt to simulate this geologically inferred behaviour and thereby test their theories of the causes of climate change. This use of models is often overlooked in debates about possible future climate change.

  4.  The only way to predict how the climate would change in the absence of anthropogenic effects is to understand the nature of past climate variability over decadal to millennial time scales. Likewise, the evaluation of climate models used to predict climate change can most convincingly be made by determining the extent to which they can fully explain what happened in the past (ie be used to "retrodict", rather than predict, the future).

  5.  The first aim of the case study is to identify "the extent to which the Government has been advised of potential alternative explanations, how these alternatives have been assessed, and what conclusions have been drawn". The Society is not in a position to make such judgements without being able to question directly ministers, their civil servants, and advisers, directly. However, the content of the recent Sir Peter Kent Lecture given to the Society by Michael Meacher2 does indicate that the Government is well aware of many of the conclusions that can be drawn from evidence of climate change contained in the geological record. Nonetheless, we suggest that the committee investigates the extent to which Government:

    —  ensures that models used to predict possible future global and regional climate changes are evaluated by testing their ability to replicate past climatic conditions based on palaeoclimatic indicators;

    —  seeks the views of a broad range of scientists in addition to those who provide information and advice as appointed advisers and consultants.

  6.  Our comments on the second aim of the Committee's inquiry are given below under the following headings:

    —  CO2 and climate change

    —  Natural climate variability

    —  How long might it take for atmospheric CO2 levels to return to normal levels?

    —  Climate modelling and the geological record

    —  Volcanic winters.


  7.  Air bubbles within Antarctic ice enable changes in the CO2 content of the atmosphere to be determined for the last 400,000 years (see cover figure). During the four warm interglacial periods similar to those the Earth has experienced for the last 10,000 years, atmospheric CO2 content reached 270-280 ppm, and during the coldest parts of glacial periods, this dropped to 190-200 ppm. Changes in atmospheric CO2 are closely correlated to changes in temperature.

  8.  What is the link between atmospheric CO2 content and temperature change? Does increasing temperature cause carbon dioxide to be released from the ocean, thereby increasing atmospheric concentration, or does increasing carbon dioxide cause temperature increase because of the greenhouse effect? We know that both processes occur. If the greenhouse effect (which is due not only to the presence of CO2 in the atmosphere, but also water vapour and methane) did not occur on Earth, its surface temperature would be 30ºC colder, and life as we know it would not exist. Equally, we know that warm tropical oceans exhale carbon dioxide, whilst cold polar oceans inhale carbon dioxide.

  9.  It is probable that the close correlations shown in the cover figure reflect close coupling of temperature and carbon dioxide, ultimately forced by changes in the amount of solar radiation reaching the Earth's surface (see second part of figure caption). If this increases and causes a rise in the Earth's surface temperature, there is net exhalation of carbon dioxide from the oceans, atmospheric CO2 increases and further greenhouse warming occurs. This in turn increases carbon dioxide exhalation, and so on, in a positive feedback loop. The reverse process follows reductions in radiation received at the surface. The question for the past is how do positive feedback loops involving carbon dioxide and temperature come to be stabilised at the glacial and interglacial levels shown in the cover figure. We do not know the answer. The question for the future is what sort of feedback loops might result from anthropogenically driven increases in atmospheric CO2. Once again we do not know the answer.


  10.  Geological and historical records show that climate change has occurred over a range of time scales, from the very slow (over millions of years) to very fast (over a few decades). The cover figure shows that over the last 400,000 years, climate has varied between cold glacial periods, and warm interglacial interludes such as the one we enjoy today. These warmer conditions only persisted for about 10 per cent of this period of time.

  11.  During the last glacial period (between 10,000 and about 110,000 years ago) there were 24 warmer interludes3: each cool-warm cycle lasted for about 1,500 years. The asymmetry of changes of temperature between the cooler and warmer interludes mirrors that which occurred over the four glacial cycles shown in the cover figure: slower stepwise cooling followed by rapid warming. This suggests that the climate system may flip rapidly from one state to another.

  12.  During the present and last interglacial periods, global temperatures were relatively stable compared to glacial periods. There is, however, some evidence to suggest that during the current interglacial there were regular changes in climate in the North Atlantic area with a periodicity of about 1,500 years4,5. These were pale shadows of much greater changes that occurred during the last glacial period. One manifestation of these changes occurs as peaks in the delivery of ice rafted debris into the North Atlantic—during colder parts of the 1,500 year climatic cycle icebergs almost reached Ireland. These temperature fluctuations were sufficiently large (about 2ºC) that, if they occurred in the future, they would have significant effects on agriculture. The "Little Ice Age" (which lasted from late medieval times until the 19th century) was the last of these cooler episodes. Warming since it ended is likely, therefore, to be due to a combination of "natural variability" and the anthropogenically driven portion of the greenhouse effect.


  13.  Since the beginnings of industrialisation at the end of the eighteenth century, the anthropogenic source of carbon dioxide has released approximately 310 gigatonnes of carbon into the atmosphere: 260 GtC (1GtC = one thousand million tonnes of carbon) from fossil fuel and cement production, and 50 GtC from terrestrial ecosystems, mainly due to changes in land use practices. It has been estimated that whereas 140 GtC of this anthropogenic output has been absorbed by the oceans, 170 GtC has accumulated in the atmosphere, with the consequence that the atmospheric concentration has reached a level unprecedented for an interglacial period (ie 360 ppm instead of the normal proportion of 280 ppm). It is increasing at a rate of 0.4 per cent per annum. Although we expect carbon dioxide and temperature to be coupled in a feedback loop, as seems to be the case with respect to past natural variations, we do not understand how and at what level a future equilibrium will be reached. However, the geological record does indicate how long it might take for atmospheric CO2 levels to return to their normal level if anthropogenic releases of CO2 were to cease immediately.

  14.  Current estimates suggest that in less than a thousand years, human activity will add 2,000-4,000 GtC to the atmosphere. Until last year, the only means of evaluating the possible climatic consequences of this huge release of carbon was to use modelling studies. However, the recent discovery that a huge blast of carbon into the atmosphere occurred 55 million years ago gives new insights not only into the nature of the global carbon cycle, but also how long it may take for the Earth's system to return to equilibrium after such a blast.

  15.  The new work6 has shown that for a brief period 55 million years ago, temperatures in the deep oceans and at high latitudes rapidly increased by 5-7ºC. Although the cause of this warming is not clear, geochemical evidence from deep-sea sediments indicates that over 1,000 GtC was released into the ocean and atmosphere. This was probably due to the release of methane from gas hydrates (a frozen form of methane plus water that is stable in low temperature and high pressure conditions) present in sediments along outer continental shelves and continental slopes. This injection of carbon occurred over less than 10,000 years, but it took 140,000 years for it to be absorbed. This suggests that if the global carbon cycle operated in a manner similar to the way it does today, we will have to wait an exceedingly long time for atmospheric CO2 levels to return to their normal interglacial levels. It should be borne in mind, however, that the Earth was much warmer 55 million years ago, so it is likely that, because the climate system operated in a different mode, rates of carbon sequestration may not have been the same as those of today.


  16.  All sophisticated climate models currently in use are based on weather forecasting models and by definition are designed and tuned to reliably simulate the present atmospheric processes and conditions. Moreover, they do not attempt to simulate all aspects of climate system processes, but employ a range of "short cuts" designed to give realistic results for our present world. Simulation and sensitivity modelling aids our understanding the causes of past climate change, and the possible variations that await us in the future, but the nature of the models has to be borne in mind when interpreting results of experiments designed to simulate globally warmer conditions.

  17.  Despite the development of ever more sophisticated climate computer models, the problem that still has to be faced is that apart from at the last glacial maximum 18,000 years ago, there is not enough high resolution palaeoclimate data available from enough locations around the world on which to base computer driven simulations of past global climate systems. For this reason, many climate modelling studies use simplified algorithms rather than trying to reproduce every detail of a past global climatic episode. In other words, models are used to explore the sensitivity of the climate system to changes in specific forcing factors, such as changes in the proportion of greenhouse gases in the atmosphere, or the distribution of land and sea around the Earth.

  18.  The more ambitious simulation models require that quantitative definitions of various components of the climate system are fed into the programme, such as incoming solar radiation, reflectivity (albedo) of land, sea and clouds, the extent of ice sheets, deep and surface oceanic temperatures, and the CO2 and water vapour content of the atmosphere etc. These general circulation models (GCMs) can only be run on very large supercomputers, and until recently, most of them could only treat the oceans as a "wet carpet", and did not simulate shallow and deep circulator patterns. Producing models of regional and global oceanic circulation is also a complex task but significant progress is being made. The reliability of the predictive output of simulation models can be assessed by comparing their outputs to present day temperature and wind patterns. However, geologic evidence shows the present world is abnormally cold in comparison to what it has been for most of the past 500 million years. If the world is indeed warming, therefore, then it is vital that the models can operate reliably for such greenhouse conditions. When existing models are used to produce simulations of past climates, say, during the Late Cretaceous (99 to 65 million years ago), or for the Eocene (55 to 34 million years ago) when global mean temperatures were 10ºC higher than today, they do not perform well. In particular continental interior climates are predicted to have been markedly colder and drier compared to what a plethora of geological evidence shows to have been the case7,8. These errors are similar, irrespective of which model is used, or which assumptions are made about the atmospheric or geographical conditions during those times. The models are demonstrably more reliable for cool world scenarios than for those for warm worlds. This may reflect the modern day origins of the models, and the intensive comparisons with data obtained from glacial periods.

  19.  The implications for successfully modelling future possibly warming point to the need to take heed of geological data. Once we have models that satisfactorily simulate present and past observations of the behaviour of the atmosphere, oceans and ice sheets, the next step is to couple them together to refine simulations of possible past climatic conditions, and to predict more confidently future climatic changes. Such advances will require not only more sophisticated simulation models, but a greatly improved knowledge of past global climate change obtained from the geological record. Crucial to this appraisal of model predictions (and retrodictions) is to compare their results with extensive geological observations. The latter can only be obtained by co-ordinated international efforts in order to make the increasingly critical tests of model predictions that Government and the international community require.


  20.  Historical records reveal that anomalous weather and climatic effects (volcanic winters9) have occurred for several years following a number of large volcanic eruptions. Such effects involve not just the environs of the volcano, but can have a significant impact on the regional, hemispheric or global scales.

  21.  The connection between lowered temperature and volcanic eruptions is due to the effects of sulphur dioxide gas released during explosive eruptions. In sufficiently powerful eruptions, volcanic rocks and gas are lofted into the upper atmosphere where the volcanogenic sulphur dioxide gas reacts with water to form micron-sized droplets of sulphuric acid gas. These aerosol droplets have the principal effect of reflecting incoming solar radiation. Consequently, the temperature of the lower atmosphere is reduced over the period taken for the aerosol to be chemically and physically destroyed.

  22.  For example, a powerful eruption of the Indonesian volcano Tambora in 1815 was followed by one to two years of unusually cold climate around the world. In Europe, annual mean temperatures were 1 to 2.5ºC lower than normal, harvests were either late or failed altogether, grain prices were at their highest and famine was widespread. During the summer of 1816, the USA experienced a widespread snowfall. The annual global mean surface temperature was about 1ºC below normal. The years 1816, 1817 and 1818 had some of the coldest Northern Hemisphere summers on record10-12.

  23.  Two further examples are the 1783 eruptions of Laki in Iceland that led to a "dry fog" permeating much of western Europe and large parts of north America, where average 1783/4 winter temperatures were up to 4.8ºC below the long term average13, and the 1991 eruption of Pinatubo (Philippines) with a 0.4ºC fall in mean global surface temperature in 199214. Eruptions that have a short term influence on climate occur irregularly but by no means infrequently. At least six such eruptions occurred in the 20th century.

  24.  The Tambora eruption in Indonesia that occurred about 70,000 years ago was one of the largest to have occurred over the past few hundred thousand years15. It occurred during a period of rapid cooling from interglacial to glacial conditions. Ice core records indicate that huge amounts of volcanic dust and aerosols that it injected into the upper atmosphere may have remained there in significant amounts for up to six years. This may have caused global cooling between 3 and 5ºC, and perhaps as much as 10ºC during growing seasons in middle to high latitudes.

  25.  Given the climatic impact of volcanic eruptions described above, and the likelihood of future eruptions, the Society recommends that the Committee investigate the extent to which the Government has explored the agricultural, economic and political consequences of volcanic winters.


  26.  The geological record provides relatively high resolution information about climate changes that have occurred over the last few hundred thousand years. This shows that there is a link between global temperatures and the greenhouse gas content of the atmosphere, but, as yet, the extent to which the latter is the cause of the former is uncertain. Palaeoclimatic records also show that global average temperatures have fluctuated by as much as several degrees in a matter of decades. Although climate models have yet to successfully simulate changes in the atmosphere-ocean-ice sheet system that result in such rapid shifts, our understanding of the system is sufficient to argue strongly for the precautionary principle to be applied in favour of reducing anthropogenically induced greenhouse gas emissions. Opponents of this approach argue that we should postpone taking effective steps to reduce these until such time as research can convincingly demonstrate the climatic impacts of emissions, and distinguish natural climatic changes from human induced ones. This implies a rather naïve faith in science to deliver certitudes. We will only obtain "proof" as the global experiment we are conducting unfolds. If this experiment triggers a rapid reorganisation of the climate system, proof might come too late for preventative action. In the meantime, continued investment in research into past climates will be crucial to providing rigorous tests of the likely effects of anthropogenic intervention into the workings of the Earth's climate system.


  1.  Petit, JR, et al, Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature, 399, 429-436 (1999).

  2.  Meacher, M, Ice age or global warming—which is it? Geoscientist 10/1, 16-17, (2000).

  3.  Bond, G, et al, Correlation between climate records from North Atlantic sediments and Greenland Ice, Nature, 342, 637-42 (1993).

  4.  Bond, G, et al, A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates. Science, 278, 1257-1265 (1997).

  5.  Campbell, ID, et al, Late Holocene 1,500 yr periodicities and their implications. Geology, 26, 471-473 (1998).

  6.  Dickens, GR, The blast from the past. Nature, 401, 742755 (1999).

  7.  Greenwood, RR, and Wing, SL, Eocene continental climates and latitudinal temperature gradients. Geology, 23, 1044-1047 (1995).

  8.  Valdes, PJ, Spicer, RA, Sellwood, BW and Palmer, DC, Understanding Past Climates: Modelling Ancient Weather. CD ROM, Gordon and Breach, Reading, UK (1999).

  9.  Rampino, MR and Self, S, Volcanism and biotic extinctions. In: Encyclopedia of volcanoes (Ed: H Sigurdsson), Academic Press, San Diego, 1083-1091 (2000).

  10.  Lamb, HH, Climate, History and the Modern World, 2nd Edition, Routledge (1995).

  11.  Stothers, RB, The great Tambora eruption in 1815 and its aftermath. Science, 224: 1191-1198 (1984).

  12.  Briffa, K, et al, Influence of volcanic eruptions on Northern Hemisphere summer temperature over the past 600 years. Nature, 393, 450-455 (1998).

  13.  Sigurdsson, H, Volcanic pollution and climate: The 1783 Laki eruption. Eos, Transactions of the American Geophysical Union, 63(32) 601-602 (1982).

  14.  McCormick, MP, et al, Atmospheric effects of the Mt Pinatubo eruption. Nature, 373: 399-404 (1995).

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