Dr Michael Hughes (Letters, 30 November) objects to an “error of fact” in our publication “What Have We Done?”, namely that harvests of maize and wheat have not “dropped since 1980 due to warmer temperatures”. The publication explained in a footnote that we are comparing projected crop yields with actual crop yields, the gap between the two accounted for by warmer temperatures, and we have now amended the online version of the document to make that clear in the body of the text. On his broader point that Cafod is wrong to campaign on the issue of climate change, we would respectfully disagree. As the Pontifical Academy of Sciences said in May 2011, “Failure to mitigate climate change will violate our duty to the vulnerable of the earth, including