Second Assessment Report (SAR)
The Second Assessment Report (SAR), published by the United Nations Intergovernmental Panel on Climate Change (IPCC) in 1995, represents a significant milestone in the understanding of human-induced climate change. Comprising three volumes focused on the science of climate change, its impacts, and economic dimensions, the SAR provided a comprehensive analysis based on contributions from approximately 1,200 authors. Notably, it marked a pivotal shift in the climate debate, moving from speculation about human activity's role to confirming a discernible human influence on global climate. The report's findings, including the continuous rise of greenhouse gas concentrations and expected future climate changes, contributed to the foundations for international negotiations, such as the Kyoto Protocol in 1997.
The SAR also sparked controversy, particularly regarding the integrity of its peer review process and its economic valuation of climate impacts, which faced scrutiny for potential biases. While it was a highly technical document, much of the public discourse centered around its summaries for policymakers, which were crafted for accessibility. Subsequent IPCC reports have built on the SAR's legacy, reflecting the evolving scientific consensus on climate change, although debates and differing perspectives persist in various spheres today.
Second Assessment Report (SAR)
- DATE: Published 1995
Definition
The United Nations Intergovernmental Panel on Climate Change (IPCC) was established by the World Meteorological Organization and the United Nations Environment Programme
to assess on a comprehensive, objective, open and transparent basis the latest scientific, technical and socio-economic literature produced worldwide relevant to the understanding of the risk of human-induced climate change, its observed and projected impacts and options for adaptation and mitigation.
The IPCC publishes a set of assessment reports at approximately five-year intervals. The IPCC’s Second Assessment Report (SAR), published in 1995, consisted of three volumes, each assembled by a separate “working group.” The three volumes of the SAR were:
- •WG I: The Science of Climate Change
- •WG II: Impacts, Adaptations, and Mitigation of Climate Change: Scientific-Technical Analyses
- •WG III: Economic and Social Dimensions of Climate Change
Together, the technical volumes were nearly two thousand pages long. Each of the volumes was summarized in a short “summary for policymakers.” The SAR was accompanied by a synthesis report that summarized information specifically relevant to Article 2 of the United Nations Framework Convention on Climate Change.
The SAR is a highly technical document that few, if any, individuals are qualified to understand in its entirety. Most discussion of the SAR is actually based on the summaries for policymakers, which were published considerably earlier than the underlying technical materials. Unlike the technical reports, the summaries for policymakers are drafted by governmental representatives to the IPCC and are formally approved by a panel comprising only a small selection of lead authors.
The SAR itself was written by a team of approximately 1,200 authors, with approximately 476 lead authors and 748 contributing authors. Authors and contributors could contribute to more than one section, so this tally is not of “unique” authors. The SAR lists 1,417 expert reviewers. The IPCC continues to publish assessment reports. The first, second, and third sections of its sixth report on climate change were finalized in August 2021, and February and April 2022. These reports looked at the impact of climate change and methods of mitigation.
Significance for Climate Change
Publication of the SAR marked a sharp turning point in the understanding of and public debate regarding climate change, as well as the need to reduce greenhouse gas emissions. While the First Assessment Report (FAR) of the IPCC (1990) had concluded only that “[t]he unequivocal detection of the is not likely for a decade or more,” the SAR concluded that “[t]he balance of evidence suggests a discernible human influence on global climate.” This attribution marked a shift in the debate from a speculative linkage to human activity to an authoritative one.
The conclusions of the SAR in the Summary for Policymakers were:
- (1) Greenhouse gas concentrations have continued to increase.
- (2) Anthropogenic aerosols tend to produce negative radiative forcings.
- (3) Climate has changed over the past century.
- (4) The balance of evidence suggests a discernible human influence on global climate.
- (5) Climate is expected to continue to change in the future.
- (6) There are still many uncertainties.
The conclusions of the SAR were accepted as definitive by world governments and served as the knowledge base used in negotiation of the Kyoto Protocol in 1997.
Perhaps because of its import in public policy development, the SAR was a source of more controversy than earlier reports. Several contributing authors to the SAR, physicists Frederick Seitz, William Nirenberg, and S. Fred Singer, accused physicist Benjamin D. Santer (lead author of a key chapter on the attribution of climate change to human activity) of making unauthorized changes to the text of the chapter after peer reviews had been concluded and final wording agreed upon by contributing authors. Santer asserted that his changes were made as a normal part of the peer review process.
Santer’s claim was supported by the chair of the IPCC as well as the other authors of the chapter, but the claims against Santer were never retracted and continue to circulate on the internet and in publications critical of the IPCC assessment report process.
In a separate controversy, the economic analysis conducted in volume 3 of the SAR was attacked for improperly using statistical values of human life that assigned more or less value to human life based on country of origin. This was the only assessment report that conducted such economic assessments of climate damage that included valuation of human mortality. The multiple sections of the Sixth Assessment Report, preliminarily completed in 2022, were compiled by working groups allowing for more cooperation and less controversy. Climate change was more widely accepted and studied in 2024 than it was in 1995, though it is not without controversy and dissenting opinions within the public and political spheres.
Bibliography
"Climate Change 1995: IPCC Second Assessment Report." UNT Digital Libraries, 10 Dec. 2024, digital.library.unt.edu/ark:/67531/metadc11834/. Accessed 19 Dec. 2024.
Houghton, John. Global Warming: The Complete Briefing. New York: Cambridge University Press, 2009.
Singer, S. Fred. Hot Talk, Cold Science: Global Warming’s Unfinished Debate. Oakland, Calif.: Independent Institute, 1998.
Sirur, Simrin, and Raghav Bikhchandani. "Why Indian Scientists Are Critiquing IPCC Report - Unfair Burden on Developing Countries." ThePrint, 5 Jan. 2023, theprint.in/environment/why-indian-scientists-are-critiquing-ipcc-report-unfair-burden-on-developing-countries/1298871/. Accessed 19 Dec. 2025.
United Nations Intergovernmental Panel on Climate Change. WG I: The Science of Climate Change. Edited by J. T. Houghton et al. New York: Cambridge University Press, 1995.
United Nations Intergovernmental Panel on Climate Change. WG II: Impacts, Adaptations, and Mitigation of Climate Change: Scientific-Technical Analyses. Edited by R. T. Watson, M. C. Zinyowera, and R. H. Moss. New York: Cambridge University Press, 1995.
United Nations Intergovernmental Panel on Climate Change. WG III: Economic and Social Dimensions of Climate Change. Edited by J. P. Bruce, H. Lee, and E. F. Haites. New York: Cambridge University Press, 1995.