A CGD note. An increasing proportion of official development assistance (ODA) is being dedicated to climate, and climate mitigation in particular. Even were that spending highly effective, and despite reaching about $30 billion in 2020, it is not large enough to finance investment that would significantly slow global climate change. But were it effective, 20 years of mitigation finance should have been significant enough to at least bend the curve on emissions in countries receiving large amounts relative to their GNI. Sadly, existing project-level and country-level evidence suggests that, in terms of carbon dioxide abated per dollar of spending, mitigation finance is a considerable distance from being highly effective. That only adds to concerns that the net costs to the world’s poorest countries of diverting development ODA to mitigation may be large. In this note I look at existing evidence and provide additional analysis to suggest past mitigation finance may have had little impact on emissions.