The multi-stage review process is an important part of an IPCC assessment. In successive stages, expert reviewers and governments are invited to comment on the accuracy and completeness of the scientific, technical and socio-economic content and the overall balance of the report drafts. The review process includes a very wide circulation among expert reviewers and government experts, with hundreds of reviewers checking the accuracy and completeness of the scientific assessment contained in the drafts. In the Expert Reviews of the IPCC Fifth Assessment Report, the three WGs encouraged as wide a participation of experts as possible, relying on a self-declaration of expertise.

The Expert Review of the First Order Draft of the WG III contribution to the IPCC Fifth Assessment Report: Climate Change 2014: Mitigation of Climate Change (WGIII AR5) took place from 16 December 2011 to 10 February 2012. Almost 1500 individuals registered as Expert Reviewers, with 659 reviewers submitting a total of 21,400 review comments. These served as the basis for discussions at the Third Lead Author Meeting, which was held in Vigo, Spain (5-9 November, 2012).

The Expert and Government Review of the Second Order Draft of the WGIII AR5 took place from 05 October to 30 November 2012. This was the opportunity for experts and governments to comment on the Second Order Draft of the chapters and the First Order Draft of the Technical Summary and the Summary for Policymakers. Observer Organizations were invited to encourage experts to sign up as expert reviewers. Over 1500 individuals registered as Expert Reviewers. The review generated 31,422 comments from 800 experts and 26 governments. These comments served as the basis for deliberations at the Fourth Lead Author Meeting, held in Addis Abbeba, Ethiopia (1-5 July 2013).

On 17 December 2013, the Final Draft of WGIII AR5 was completed, comprising 16 Chapters, 3 Annexes, a Technical Summary and a Summary for Policymakers. The Final Draft was made available to the Governments during the Final Government Distribution from 17 December 2013 to 16 February 2014, The Final Government Distribution provided governments with an opportunity to submit written comments on the Final Draft Summary for Policymakers in preparation of the Twelfth Session of Working Group I. A total of 1855 comments were received from 32 governments.

In accordance with Article 4.2 of Appendix A to the Principles Governing IPCC Work, all comments submitted as part of the formal expert and/or government review together with the author responses will be made available on the WGIII AR5 web site as soon as possible after finalization of the report.