220 Weighingthe uncertainty
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 cli-
mate 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 third as-
sessment report in 2001, these numbers had grown to 123 lead authors
and 516 contributing authors involved with the various chapters, together
with 21 review editors and 420 expert reviewers involved in the review
process.
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 thescience to policymakers with accuracy and clarity. The ple-
nary meeting which agreed unanimously the 2001 SPM, held in Shanghai
in January 2001,was attended by representatives of 99 countries and 45
scientists representing the lead authors of the scientificchapters together
with a number of 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.
I have given these details of the work of the Science Assessment
Group in order to demonstrate the degree of commitment of the scientific