Today the idea that climate change requires a gradual and moderate response no longer commands consensus support among economists. A more demanding approach is gaining ground. This paper traces the changes in economic thinking concerning the case for action on climate change, through an analysis of the work of three eminent economists: William Nordhaus, Nicholas Stern and Ross Garnaut. It shows how from Nordhaus to Stern to Garnaut the case for more urgent and radical mitigation has been strengthened as temperature targets have been lowered and business-as-usual emissions projections raised. It also shows that Stern and especially Nordhaus, who has been working on this subject the longest, have changed their own views in favour of more urgent and radical mitigation. Some disagreements remain between these three economists, and some other economists have more moderate views, but the old consensus has been shattered.