In May, the Copenhagen Consensus ( brought 38 of the world's top economists to Denmark to make a prioritized list of solutions to global challenges. In his critical judgement of the consensus, “Seeking a global solution” (Nature 430, 725–726; 2004), Jeffrey Sachs misunderstood the project in three fundamental ways.

First, Sachs asserted that, because the world has promised to spend much more than the US$50 billion discussed by the Copenhagen Consensus, prioritization is unnecessary. But more or less money would not alter the project's outcome. If more than $50 billion were marshalled, the consensus list would simply show where the extra money should be directed.

The claim that the developed world has promised to substantially increase development assistance should be treated with caution: since 1970 the United Nations has wanted such spending to double as a percentage of GNP, but it has fallen substantially since then (see It seems unrealistic to assume that the resources allocated will be so large that we will not have to prioritize. The $50 billion was chosen as an example of a realistic commitment to additional spending.

Second, Sachs' criticism that the Copenhagen Consensus consisted solely of economists missed the very point of the project. Economists have expertise in economic prioritization. It is they and not climatologists or malaria experts who can prioritize between battling global warming or communicable disease. Of course, all economic estimates are based squarely on the best natural-science models.

Third, in discussing why efforts to handle climate change ended up at the bottom of the Copenhagen Consensus list, Sachs left the distorted impression that all climate economists believed the relatively high carbon-tax proposal should have been given a higher priority. In fact, two of the three climate economists explicitly found the costs exceeded the benefits. The expert panel endorsed this view.

The Copenhagen Consensus was the first project to prioritize the major challenges facing the world. Morally we must focus on the best priorities first, or we do less good for humanity. Prioritization means not everything is done first. This often makes good people fret because ‘we should do everything’, although we do not and cannot.

That a prominent economist such as Sachs should posit such flawed arguments underlines the case both for the Copenhagen Consensus and for a continued public discourse on prioritization.