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Preface
This report is the first complete assessment of the science of
climate change since Working Group I (WGI) of the IPCC produced
its second report Climate Change 1995: The Science of Climate
Change in 1996. It enlarges upon and updates the information contained
in that, and previous, reports, but primarily it assesses new
information and research, produced in the last five years. The
report analyses the enormous body of observations of all parts
of the climate system, concluding that this body of observations
now gives a collective picture of a warming world. The report
catalogues the increasing concentrations of atmospheric greenhouse
gases and assesses the effects of these gases and atmospheric
aerosols in altering the radiation balance of the Earth-atmosphere
system. The report assesses the understanding of the processes
that govern the climate system and by studying how well the new
generation of climate models represent these processes, assesses
the suitability of the models for projecting climate change into
the future. A detailed study is made of human influence on climate
and whether it can be identified with any more confidence than
in 1996, concluding that there is new and stronger evidence that
most of the observed warming observed over the last 50 years is
attributable to human activities. Projections of future climate
change are presented using a wide range of scenarios of future
emissions of greenhouse gases and aerosols. Both temperature and
sea level are projected to continue to rise throughout the 21st
century for all scenarios studied. Finally, the report looks at
the gaps in information and understanding that remain and how
these might be addressed.
This report on the scientific basis of climate change is the
first part of Climate Change 2001, the Third Assessment Report
(TAR) of the IPCC. Other companion assessment volumes have been
produced by Working Group II (Impacts,
Adaptation and Vulnerability) and by Working Group III (Mitigation).
An important aim of the TAR is to provide objective information
on which to base climate change policies that will meet the Objective
of the FCCC, expressed in Article 2, of stabilisation of greenhouse
gas concentrations in the atmosphere at a level that would prevent
dangerous anthropogenic interference with the climate system.
To assist further in this aim, as part of the TAR a Synthesis
Report is being produced that will draw from the Working Group
Reports scientific and socio-economic information relevant to
nine questions addressing particular policy issues raised by the
FCCC objective.
This report was compiled between July 1998 and January 2001,
by 122 Lead Authors. In addition, 515 Contributing Authors submitted
draft text and information to the Lead Authors. The draft report
was circulated for review by experts, with 420 reviewers submitting
valuable suggestions for improvement. This was followed by review
by governments and experts, through which several hundred more
reviewers participated. All the comments received were carefully
analysed and assimilated into a revised document for consideration
at the session of Working Group I held in Shanghai, 17 to 20 January
2001. There the Summary for Policymakers was approved in detail
and the underlying report accepted.
Strenuous efforts have also been made to maximise the ease of
utility of the report. As in 1996 the report contains a Summary
for Policymakers (SPM) and a Technical
Summary (TS), in addition to the main chapters in the report.
The SPM and the TS follow the same structure, so that more information
on items of interest in the SPM can easily be found in the TS.
In turn, each section of the SPM and TS has been referenced to
the appropriate section of the relevant chapter by the use of
Source Information, so that material in the SPM and TS can easily
be followed up in further detail in the chapters. The report also
contains an index at Appendix
VIII, which although not comprehensive allows for a search
of the report at relatively top-level broad categories. By the
end of 2001 a more in-depth search will be possible on an electronic
version of the report, which will be found on the web at http://www.ipcc.ch.
We wish to express our sincere appreciation to all the Co-ordinating
Lead Authors, Lead Authors and Review Editors whose expertise,
diligence and patience have underpinned the successful completion
of this report, and to the many contributors and reviewers for
their valuable and painstaking dedication and work. We are grateful
to Jean Jouzel, Hervé Le Treut, Buruhani Nyenzi, Jim Salinger,
John Stone and Francis Zwiers for helping to organise drafting
meetings; and to Wang Caifang for helping to organise the session
of Working Group I held in Shanghai, 17 to 20 January 2001.
We would also like to thank members of the Working Group I Bureau,
Buruhani Nyenzi, Armando Ramirez-Rojas, John Stone, John Zillman
and Fortunat Joos for their wise counsel and guidance throughout
the preparation of the report.
We would particularly like to thank Dave Griggs, Maria Noguer,
Paul van der Linden, Kathy Maskell, Xiaosu Dai, Cathy Johnson,
Anne Murrill and David Hall in the Working Group I Technical Support
Unit, with added assistance from Alison Renshaw, for their tireless
and good humoured support throughout the preparation of the report.
Thanks go to Christoph Ritz and Bettina Buechler of ProClim (Forum
for Climate and Global Change), a programme of the Swiss Academy
of Sciences in Bern for their assistance in producing the index
to this report. We would also like to thank Narasimhan Sundararaman,
the Secretary of IPCC, Renate Christ, Deputy Secretary, and the
staff of the IPCC Secretariat, Rudie Bourgeois, Chantal Ettori
and Annie Courtin who provided logistical support for government
liaison and travel of experts from the developing and transitional
economy countries.
Robert Watson
IPCC Chairman
John Houghton
Co-chair IPCC WGI
Ding Yihui
Co-chair IPCC WGI
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