The Intergovernmental Panel on Climate Change (IPCC) recognises that climate change is a moral problem or, to use its cautious language, it ‘raises ethical issues’. The authors of the IPCC’s recent Fifth Assessment Report therefore included two moral philosophers. I am one of them. I have been a member of the IPCC’s Working Group 3 since 2011. The writing process was exhaustive and exhausting. Our report went through three full drafts before the final version. Each was sent out for comments to very large numbers of people, including academic experts and representatives of governments. We were required to take note of every comment, and to record what we had done about it. I dealt with about 600 comments in this way; Working Group 3 as a whole dealt with 38,000. The aim was to produce the broadest possible consensus, reporting on the state of knowledge about climate change. I think we did that. It inevitably meant we had to be conservative in our judgments. The outcome is a 2000-page report, which has already been published on the internet. Because no one will read a report of that size, our efforts in the last few months have gone into writing two summaries. A subgroup of authors from Working Group 3 hammered them out over the last eight months. The fuller and more reliable one is the Technical Summary. The name puts people off reading it, but actually it is not particularly technical. It is simply a summary of the main report. The shorter, 30-page précis known as the Summary for Policymakers (SPM) attracts more attention but is subject to political influence.