The IPCC's First Assessment: Bringing Climate Research into a Public Report

In 1990, the Intergovernmental Panel on Climate Change (IPCC) completed its First Assessment Report, organizing knowledge scattered across meteorology, oceanography, ecology and energy research into material that countries could discuss together. The World Meteorological Organization and United Nations Environment Programme had established the body in 1988, with Swedish meteorologist Bert Bolin as its first chair. The report was neither the result of a single new experiment nor an agreed emissions-reduction treaty, but an assessment at that stage of the evidence, disputes and possible actions.

One difficulty was that different questions carried different degrees of certainty. The mechanism by which greenhouse gases absorb radiation, warming measured by instruments, future emissions pathways and changes in a particular region's rainfall could not be treated as conclusions at the same level. Through a division of work and connections between its parts, the First Assessment placed these questions within a traceable structure of argument.

References: [1] [3]

Working Group I, chaired by John Houghton, was responsible for the scientific assessment; Houghton, Jenkins and Ephraums edited the published science volume. Its chapters progressed from greenhouse gases and radiative forcing through model processes, model evaluation, observed changes, detection of an anthropogenic signal and sea level. Working Group II, chaired by Yuri Izrael, brought together discussion of impacts on agriculture, forests, water resources, coasts and human settlements. Working Group III examined energy, land use, coastal management and economic and legal measures.

Writing and review followed an explicit iterative process. The first draft of Working Group I's Summary for Policymakers was discussed at a lead authors' meeting in Edinburgh in February 1990. The second draft and main text went to experts and relevant scientific programs for review, and a third draft incorporating comments was discussed and agreed at the May plenary in Windsor. Working Group II's report also underwent technical review, with an Australian editorial team responsible for compilation. The public reports thus offered both specialist chapters and summaries for policy discussion.

References: [1] [2] [3]

The scientific volume concluded that human activities were increasing atmospheric concentrations of greenhouse gases such as carbon dioxide and would enhance the greenhouse effect. It also reported that global mean surface temperature had risen by about 0.3 to 0.6 degrees Celsius over roughly the preceding century. Understanding of natural variability and observational records were still limited at the time, so all the measured warming could not be attributed directly to human activities. Physical mechanisms, observations and attribution judgments were presented separately to avoid substituting one kind of evidence for another.

Future changes also depended on emissions assumptions. Under a class of scenarios then called business as usual, models gave a best estimate of global mean warming over the following century of about 0.3 degrees Celsius per decade, with a broad range around it. This was not a timetable that would occur under every societal pathway. By feeding different emissions scenarios into models and comparing temperature and sea-level responses, the report made it possible to discuss how energy choices could alter long-term risks.

References: [1]

Working Group II noted low confidence in projections of regional rainfall and soil moisture, uncertainty that carried over into judgments about crop yields, irrigation needs and ecosystem impacts. Rather than stopping at a graph of global temperature, its chapters separately examined agriculture and forestry, hydrology, settlements and coasts. A global average temperature increase could not automatically determine how much water storage a particular basin needed or directly calculate local losses for a crop.

Working Group III then separated possible responses into practical categories: energy and industrial efficiency, forest and agricultural management, coastal adaptation, and technology transfer, finance, markets and legal institutions. Impact assessment indicated where risks might fall, while response assessment showed the resources and institutions needed for action. They supplied a comparative framework without deciding countries' specific emissions obligations or cost-sharing arrangements.

References: [2] [3]

On December 21, 1990, the United Nations General Assembly adopted Resolution 45/212, establishing an intergovernmental negotiating process intended to complete a climate framework convention before the 1992 United Nations Conference on Environment and Development. The resolution also asked the relevant secretariat to work with the IPCC to obtain objective scientific and technical advice needed for negotiations. This linked assessment with treaty-making, but the negotiating committee had its own organization and government representatives and was not identical to the body of report authors.

The 1992 United Nations Framework Convention on Climate Change resulted from subsequent political negotiations; the 1990 event was the completion of the first comprehensive assessment. A key practice it left was to state conclusions, conditions and unknowns separately, then revise them through later assessments as observations and research expanded. Public knowledge of climate thus became an ongoing task of maintenance, rather than a single report that settled every question.

References: [4] [1]