Climate finance is becoming a dark curve on the road from Copenhagen to Cancún. Poorer nations fear that richer ones will fulfil the US$30 billion ‘fast-start’ climate finance promises made in the non-binding Copenhagen Accord by relabelling or diverting basic development aid, or by simply delivering on past climate finance pledges. The problem is simple: contributor countries are operating with no clear baseline against which their promise of ‘new and additional’ funding can be counted – and they do not accept the baselines put forth by developing countries. A viable solution for the short term is to use projections of business-as-usual development assistance as baselines. The longer-term benchmark could be the provision of truly ‘new’ funds from new funding sources. Substantial up-front negotiations may be required, but seizing this opportunity to define baselines will build confidence on both sides and create predictability for future finance.