This paper will examine the First Assessment Cycle of the Intergovernmental Panel on Climate Change (IPCC). Beginning in November 1988 the IPCC began a three-pronged process to: (i) Assess the scientific information related to climate change; (ii) assess the environmental and socio-economic impacts of climate change and; (iii) identify possible realistic policy and strategic responses for management of climate change. During this phase the IPCC panel members and working group chairs and lead authors contributed to an ad hoc approach producing “an authoritative statement of the views of the international scientific community at [that] time”(IPCC, 1990). At the outset of this process it wasn’t at all clear that the IPCC would evolve into the authoritative forum for addressing climate change. But with the reports of the first assessment given pride of place at the Second World Climate Conference in 1990 the IPCC was clearly viewed by the scientific community as a credible organisation. Moreover, the institutional design of the IPCC –involving governments in the review stage –enabled considerable political buy-in. The strict timelines, governmental ownership and the involvement of several eminent scientists in the process meant politicians were interested, scientists engaged and the information produced was highly relevant and credible. In this paper I will investigate the decisions and processes that contributed to the anchoring of the IPCC as the central authority on climate related knowledge. It was during this assessment that the credibility, saliency and legitimacy of the IPCC was established. Ensuring the authority of the IPCC accelerated the political movement towards the framework convention on climate change, signed into force at the Rio Summit in 1992. The decision of US policymakers to establish an assessment mechanism with an intergovernmental structure was a concerted effort to ‘reign in out of control science-policy entrepreneurs.’ This ultimately backfired as the scientific community produced the most authoritative, credible and widely legitimate report on climate change to date backing up the earlier findings so unpopular among US policymakers –namely a proposal for a framework convention on climate change.