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


Memorandum submitted by the Climatic Research Unit, University of East Anglia, Norwich


  1.  The Climatic Research Unit (CRU) has been in existence for 28 years. It receives funding from several sources (eg UK government departments, EU, US Department of Energy, UK Research Councils, Industry/Business and organizations with charitable status) and is partially supported by the University of East Anglia, through the School of Environmental Sciences. Over this time, it has built up an excellent reputation for work in the Climate Change field. It is most well-known for its studies on instrumental climate (jointly producing with the Hadley Centre of the Meteorological Office the time series of hemispheric/global temperatures used by IPCC), paleoclimate (past estimates of temperature for the last few millennia) and projections of future climate (again joint work with the Hadley Centre). CRU is the dissemination point for all climate model data from the Hadley Centre (funded by DETR, Department of Environment, Transport and the Regions, through the Climate Impacts Link project), adding value/details to future scenario integrations of Hadley Centre models. This includes validating the models against observational fields. As an academic institution, CRU does not have a position on this, or any other matter. The views expressed here are the synthesis of individual members who have worked in this area.

  2.  This memorandum will address the five specific questions, referring back as appropriate to the terms of reference.

Q1.  What other reasonable explanations, other than increasing concentrations of CO2 in the atmosphere, are you aware of for the upward trend in earth temperatures? Has your organization conducted any assessment of these alternatives and if so, with what conclusions?

  3.  First, CO2 is not the only human-produced greenhouse gas. There are also CH4, N2O and CFCs, often referred to collectively as greenhouse gases. CO2 alone is only about 60 per cent of the problem. Aerosol emissions (eg sulphates, soot, and some other particulates) are also considered as part of the problem. Aerosols have an inverse effect (ie should lead to cooling) but their use is being reduced on other pollution grounds (eg they are the root cause of acid rain). The question is taken, therefore, to refer to "Anthropogenic emissions or activities, which alter the radiative balance within the atmosphere", or the loose media phrase "global warming", ie not-natural.

  4.  There are only two possible natural factors that could potentially affect global scale temperature changes, on the annual-to-century timescales (ie similar to that of anthropogenic activities). These are variations in solar output and the effects of large explosive volcanic eruptions.

  5.  It has been shown that large explosive volcanic eruptions (particularly those in the tropics and subtropics, 30ºN-30ºS), over the past century, have caused short-term climate change. Mt Pinatubo in the Philippines, for example, erupted in June 1991, and caused a global average cooling during 1992 and 1993 (mainly from May to September, ie northern summers) of about 0.3ºC (see, eg, Kelly et al, 1996). Larger eruptions in earlier centuries may have caused greater reductions in temperature. The number of volcanic events over the last 600 years is relatively few (-20 in total, see Briffa et al, 1998).

  Impacts might become larger if volcanoes erupted together compounding effects, but there is no evidence of this happening, except in the late 17th century and the 1810s. The only significant eruptions this century occurred in 1902, 1912, 1963, 1982 and 1991.

  6.  Global temperatures also vary on timescales of three to five years as a result of changes in the tropical Pacific Ocean (El Niño/La Niña events). El Niño events cause warmer years globally and La Niña cooler ones. Changes in the frequency/severity of these events have occurred over the last 150 years, but not to an extent to cause any change in global scale climate on decadal and longer timescales.

  7.  It is known that the Sun's output varies on many timescales, but we have only recently begun to realise exactly how by monitoring the Sun above the atmosphere using instrumentation on satellites. Ground based measures of solar output are available for several centuries but they are influenced by the atmosphere. Despite this, several estimates of past variations in solar output have been made which extend back several centuries. Variations in solar output have been considered as being important by scientists since the 18th century. The possibility that solar variability might account for all or part of the global warming trend has been examined by Kelly and Wigley (1990, 1992) in a series of studies that have assessed the relative contribution of solar forcing of climate, based on sunspot numbers and solar cycle length and anthropogenic activities. The overall conclusion of this work is that although there is evidence that solar variability may affect global temperature on these timescales, the effect is markedly less than that resulting from anthropogenic activities. In other words, these authors and all in CRU would conclude that anthropogenic activity is the most plausible explanation for the bulk of the observed warming trend.

Q2.  What critical appraisal of climate change models has your organisation performed and with what result?

  8.  First, there is no such thing as a climate change model. Climate models solve the equations of physics (mass, energy, momentum) and the climate model run in the UK by the Hadley Centre is essentially the same computer code that produces each day's weather forecasts. The models are run in (control) present mode and then the models atmospheric composition is altered to produce a perturbed (scenario) integration. The change produced by the model is the difference between the perturbed and control integrations. We have extensively evaluated the performance of the control runs of General Circulation Models (GCMs) over at least the last 10 years in projects funded by DETR. The results of this work have obviously gone to DETR as annual and project reports and also as publications to the peer-review literature (see, eg, Hulme et al, 1993; Airey and Hulme, 1995, Osborn et al, 1999). The basic conclusions of these studies are:

    —  GCMs have improved over the last 10 years (as have weather forecasts);

    —  the Hadley Centre model is considered by most atmospheric scientists to be one of the best two in the world at the moment (the other is at the Max Planck Institute for Meteorology, Hamburg, Germany). The USA has diversified its effort into a number of centres and has fallen behind. If research there was more co-ordinated, it ought to improve; and

    —  the latest two Hadley Centre models (HadCM2 and HadCM3) do very well at simulating the climate over the UK and Europe, reproducing features and interrelationships between surface climate (temperature and precipitation patterns) and the circulation that occur in the real world (see references above).

Q3.  How much agreement is there between scientists internationally regarding explanations for climate change?

  9.  The most comprehensive assessment of explanations for climate change are given in the reports of the Intergovernmental Panel on Climate Change (IPCC) in 1990 and 1995. Most of the world's leading scientists are involved in contributing to the reports and most would agree with the main conclusions. The large majority of atmospheric scientists would accept IPCC's most quoted conclusion that "The balance of evidence suggests a discernible human influence on global climate". There will be differences of opinion on some of the details but all atmospheric scientists would accept that IPCC provides the concensus view. IPCC and climate scientists both accept there are knowns and unknowns, with respect to the causes of climate change, but there are no great schisms within the community regarding what the important mechanisms are. This concensus has been there since CRU began in the 1970s and predates IPCC.

Q4.  To what extent are the fruits of your research fed into Government machinery and by what means? Do you think that the Government is made sufficiently aware of alternative explanations? By what means does this occur?

  10.  The results of our research reach the government macinery in a number of ways: through direct contact with politicians (ministers and MPs), through contract reports to departments such as DETR (informing also our contract officers when important papers will appear in journals like Nature and Science), through collaboration with government scientists (eg the Hadley Centre of the Met. Office and NERC Research Institutes), through publications in the scientific literature, and through media. We also inform other departments, such as MAFF and DoH, and advise the UK Climate Impacts Programme (funded by DETR). Over the last few years we have occasionally been consulted by DETR concerning statements made by ministers in the House and elsewhere. In our view, the government is totally briefed on our research results regarding the causes of climate change, validation of GCMs, and observed changes in a global and UK climate. We always emphasise areas of uncertainty, although these are often missed by the media who like things to be black and white.

  11.  Our belief is that there are no credible alternative explanations (ie the 0.6ºC increase in global temperatures during the 20th century cannot be explained without including a major component from anthropogenic emissions to the atmosphere). We hear, occasionally, of alternatives (all in the grey literature or on web pages). In the climate area, as in all science, credibility is measured by publication in an appropriate peer-review journal. As climatologists we intuitively rank journals, depending on our knowledge of how easy/difficult it is to get articles published (ie how rigorous the journal's reviewing policy is). CRU would rank the following journals; Nature, Science, J. Climate, J. Geophysical Research, Climate Dynamics, the International Journal of Climatology and Geophysical Research Letters in the premier league. We mention this, as any alternative explanations should appear in these sort of journals for them to have any credence. Anyone can publish a book or set up a web page to expound their views. This is not what we understand as scientific publication. If alternative explanations were published in these journals we would be the first to be informing departments like DETR.

Q5.  How important is the International (sic) Panel of Climate Change in co-ordinating research on climate change and disseminating findings (sic)?

  12.  The IPCC does not co-ordinate research into climate change. Its role is to review existing research and to advise the international community on the current state of scientific and technical understanding. In this respect, IPCC makes authoritative statements but only based on material published in the peer-reviewed scientific literature. In this way it plays a crucial role in disseminating research findings by reaching a concensus judgement of all the published literature on the subject.

  13.  The IPCC does not fund any scientific research. In the UK, the Technical Support Unit for Working Group 1, funds scientists involved in writing drafts of chapters to attend co-ordination meetings, where the lead authors get together. The IPCC's recommendations regarding the current issues in climate (eg what we need to know more about to reduce uncertainties) does influence funding in indirect ways, but only alongside a host of other factors.

15 February 2000


  These references are those specifically referred to in this memorandum. CRU has written several hundred scientific papers. Of the names on these papers, CA Senior and SFB Tett work at the Hadley Centre and FH Schweingruber at the Swiss National Institute of Forest, Snow and Landscape research. All others are or were members of CRU at the time the papers were published.

  Airey, M and Hulme, M, 1995: Evaluating climate model simulations of precipitation: methods, problems and performance. Prog Phys Geog 19, 427-448.

  Briffa, KR, Jones, PD, Schweingruber, FH and Osborn, TJ, 1998: Influence of volcanic eruptions on Northern Hemisphere summer temperatures over 600 years. Nature 393, 450-455.

  Hulme, M, Briffa, KR, Jones, PD, and Senior, CA, 1993: Validation of GCM control simulations using indices of daily airflow types over the British Isles. Climate Dynamics 9, 95-105.

  Kelly, PM and Wigley, TML, 1990: The influence of solar forcing trends on global mean temperature since 1861. Nature 347, 460-462.

  Kelly, PM and Wigley, TML, 1992: Solar cycle length variations, greenhouse forcing and global climate. Nature 360, 328-330.

  Kelly, PM, Pengqun, J and Jones P D, 1996: The spatial response of the climate system to explosive volcanic eruptions. Int J Climatol 16, 537-550.

  Osborn, TJ, Briffa, KR, Tett, SFB, Jones, PD and Trigo, RM, 1999: Evaluation of the North Atlantic Oscillation as simulated by a coupled climate model. Climate Dynamics 15, 685-702.

previous page contents next page

House of Commons home page Parliament home page House of Lords home page search page enquiries index

© Parliamentary copyright 2001
Prepared 21 March 2001