The IPCC Assessments

Because of the scientific uncertainty, it has been necessary to make a large effort to achieve the best assessment of present knowledge and to express it as clearly as possible. For these reasons the IPCC was set up jointly by two United Nations' bodies, the World Meteorological Organization (WMO) and the

United Nations Environmental Programme (UNEP).3 The IPCC's first meeting in November 1988 was timely; it was held just as strong political interest in global climate change was beginning to develop. The Panel realised the urgency of the problem and, under the overall chairmanship of Professor Bert Bolin from Sweden, established three working groups, one to deal with the science of climate change, one with impacts and a third one to deal with policy responses. The IPCC has produced four main comprehensive Reports,4 in 1990, 1995, 2001 and 2007, together with a number of special reports covering particular issues. Previous chapters have already referred widely to these reports.

I would like to say more about the Physical Science Assessment Working Group (of which I was chairman from 1988 until 1992 and co-chairman from 1992 until 2002).5 Its task has been to present in the clearest possible terms our knowledge of the science of climate change together with our best estimate of the climate

Impacts

Figure 9.1 The cascade of uncertainties in projections to be considered in developing climate and related scenarios for climate change impact, adaptation and mitigation assessment.

change over the twenty-first century that is likely to occur as a result of human activities. In preparing its reports the Working Group realised from the start that if they were to be really authoritative and taken seriously, it would be necessary to involve as many as possible of the world scientific community in their production. A small international organising team was set up at the Hadley Centre of the United Kingdom Meteorological Office at Bracknell and through meetings, workshops and a great deal of correspondence most of those scientists in the world (both in universities and government-supported laboratories) who are deeply engaged in research into the science of climate change were involved in the preparation and writing of the reports. For the first report, 170 scientists from 25 countries contributed and a further 200 scientists were involved in its peer review. For the Fourth Assessment Report in 2007, these numbers had grown to 152 lead authors and over 500 contributing authors and over 600 involved in the two-stage review process during which 30 000 written review comments were received and processed.

In addition to the comprehensive, thorough and intensively reviewed background chapters that form the basic material for each assessment, each report includes a Summary for policymakers (SPM), the wording of which is approved in detail at a plenary meeting of the Working Group, the object being to reach agreement on the science and on the best way of presenting the science to policymakers with accuracy and clarity. The plenary meeting which agreed unanimously the 2007 SPM, held in Paris in January 2007, was attended by representatives of 113 countries, a number of scientists representing the lead authors of the scientific chapters together with representatives from non-governmental organisations. There has been very lively discussion at these plenary meetings, most of which has been concerned with achieving the most informative and accurate wording rather than fundamental dispute over scientific content.

During the preparation of the reports, a considerable part of the debate amongst the scientists has centred on just how much can be said about the likely climate change in the twenty-first century. Particularly to begin with, some felt that the uncertainties were such that scientists should refrain from making any estimates or predictions for the future. However, it soon became clear that the responsibility of scientists to convey the best possible information could not be discharged without making estimates of the most likely magnitude of the change coupled with clear statements of our assumptions and the level of uncertainty in the estimates. Weather forecasters have a similar, although much more short-term, responsibility. Even though they may feel uncertain about tomorrow's weather, they cannot refuse to make a forecast. If they do refuse, they withhold from the public most of the useful information they possess. Despite the uncertainty in a weather forecast, it provides useful guidance to a wide range of people. In a similar way the climate models, although subject to uncertainty, provide useful guidance for policy.

An important feature of the Third and Fourth Science Assessments has been the presentation of uncertainty wherever possible in terms of probabilities. Words to express uncertainty have been associated with probabilities, for instance, very likely (more than 90% probability), likely (more than 67%), etc. This has substantially increased the value of future climate projections especially when considering the impacts of climate change and policy concerning adaptation to them.

I have given these details of the work of the Physical Science Assessment Group in order to demonstrate the degree of commitment of the scientific community to the understanding of global climate change and to the communication of the best scientific information to the world's politicians and policymakers. After all, the problem of global environmental change is one of the largest problems facing the world scientific community. No previous scientific assessments on this or any other subject have involved so many scientists so widely distributed both as regards their countries and their scientific disciplines. The IPCC Reports can therefore be considered as authoritative statements of the contemporary views of the international scientific community.

A further important strength of the IPCC is that, because it is an intergovernmental body, governments are involved in its work. In particular, government representatives assist in making sure that the presentation of the science is both clear and relevant from the point of view of the policymaker. Having been part of the process, governments as well as scientists are in a real sense owners of the resulting assessments - an important factor when it comes to policy negotiations.

In the presentation of the IPCC assessments to politicians and policymakers, the degree of scientific consensus achieved has been of great importance in persuading them to take seriously the problem of global warming and its impact. In the run-up to the United Nations Conference on Environment and Development (UNCED) at Rio de Janeiro in June 1992, the fact that they accepted the reality of the problem led to the formulation of the international Framework Convention on Climate Change (FCCC) which was signed by over 160 countries -President George Bush, Snr, signed for the United States and the United States Senate subsequently unanimously ratified it. It has often been commented that without the clear message that came from the world's scientists, orchestrated by the IPCC, the world's leaders would never have agreed to sign the Climate Convention.

After the publicity arising from the Earth Summit in 1992, debate concerning the scientific findings of the IPCC intensified in the world's press. Some of this

Rajendra Pachauri, chairman of IPCC, and other members of the IPCC delegation with Al Gore at the Nobel Peace Prize celebrations in Oslo, December 2007.

was honest scientific debate - argument and debate are, after all, intrinsic to the scientific process. Some, however, was stimulated by strong vested interests particularly in the United States that attempted to discredit the work of the IPCC and to persuade the public at large either of the absence of scientific evidence for global warming or even if it were occurring that it was not an issue requiring urgent attention.6 From my standpoint from within the IPCC, these attacks tended to lead to enhanced clarity and accuracy in our reports although for the public at large the propagation of so much misleading material created a great deal of misunderstanding and confusion.7

Over the past 20 years as the global climate has steadily warmed and scientific effort to understand climate change has grown, evidence that climate change is bringing with it serious adverse impacts has continued to strengthen and to be widely recognised. This is well illustrated by the statement published in June 2005 by the Academies of Science of the world's 11 most important countries (the G8 plus India, China and Brazil) endorsing the conclusions of the IPCC and urging the governments meeting at the G8 summit that year in Edinburgh to take urgent action to address climate change.8 The world's top scientists could not have spoken more strongly. A further endorsement of the IPCC and its work came in 2007 with the award of Nobel Peace Prizes to the IPCC and to Al Gore.

I have illustrated the work of the IPCC by describing in some detail the activity of the Physical Science Assessment Working Group. The IPCC has two other Working Groups that have followed similar procedures and have dealt with the Impacts of Climate Change, with Adaptation and Mitigation strategies and with the Economics and Social Dimensions of Climate Change. Contributions to their work have not only come from natural scientists; increasingly social scientists, especially economists, have become involved. In these social science areas much fresh ground has been broken as consideration has been given to questions of what, in the global context, might form the basis of appropriate political and economic response to climate change. The rest of this chapter and the following chapters will draw heavily on their work.

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