Bjorn Lomborg’s Copenhagen Consensus met in Denmark in the last week of May. The project described itself as follows:

“The goal of the Copenhagen Consensus project was to set priorities among a series of proposals for confronting ten great global challenges. These challenges, selected from a wider set of issues identified by the United Nations, are: civil conflicts; climate change; communicable diseases; education; financial stability; governance; hunger and malnutrition; migration; trade reform; and water and sanitation.

“A panel of economic experts, comprising eight of the world’s most distinguished economists, was invited to consider these issues. The members were Jagdish Bhagwati of Columbia University, Robert Fogel of the University of Chicago (Nobel laureate), Bruno Frey of the University of Zurich, Justin Yifu Lin of Peking University, Douglass North of Washington University in St Louis (Nobel laureate), Thomas Schelling of the University of Maryland, Vernon Smith of George Mason University (Nobel laureate), and Nancy Stokey of the University of Chicago.”

The project ranked four projects as representing very good value for money. They were: new programs to prevent the spread of HIV/AIDS; reducing the prevalence of iron-deficiency anemia by means of food supplements; multilateral and unilateral of tariffs and non-tariff barriers, together with the elimination of agricultural subsidies; and the control and treatment of malaria.

On climate change, the Consensus project considered a paper authored by William R. Cline of the Center for Global Development and Institute for International Economics, which suggested that the benefits of action now on climate change would outweigh the costs by $166 trillion to $94 trillion. However, the only way the paper was able to achieve such a benefit: cost ration was by using an unfeasibly low discount rate for the benefits of 1.5 percent. The panel rejected this economically nonsensical methodology.

In fact the panel ranked all three suggestions for action – an “optimal carbon tax,” a “value-at-risk carbon tax” and the Kyoto protocol as bad investments. The final report summarized:

“The panel looked at three proposals, including the Kyoto Protocol, for dealing with climate change by reducing emissions of carbon. The expert panel regarded all three proposals as having costs that were likely to exceed the benefits. The panel recognized that global warming must be addressed, but agreed that approaches based on too abrupt a shift toward lower emissions of carbon are needlessly expensive. The experts expressed an interest in an alternative, proposed in one of the opponent papers, that envisaged a carbon tax much lower in the first years of implementation than the figures called for in the challenge paper, rising gradually in later years. Such a proposal however was not examined in detail in the presentations put to the panel, and so was not ranked. The panel urged increased funding for research into more affordable carbon-abatement technologies.”

So is this all bad news for climate alarmists? You wouldn't think so if you read the Denver Post:

In addition to oil prices hovering at record levels, some economists say a carbon tax would encourage Americans to curb wasteful energy consumption that contributes to global warming.

Three prominent economists appearing here for the global economics conference "Copenhagen Consensus" agreed that the chances of approving a carbon tax during an election year are slim. Consumers would face the tax at the gas pump. ...

A carbon tax would be a more efficient means of addressing problems tied to global warming than many other measures that have won favor on the world stage, according to the economists: William Cline, a senior fellow at the Institute for International Economics and the Center for Global Development in Washington, D.C.; Harvard University professor Robert Mendelsohn; and Stanford University professor Alan Manne.

... While the men agree that a carbon tax would be one financially sound way to fight global warming, they disagree about how high the tax should be.

Quite how this squares with the final report of the consensus project - that three out of the four carbon tax proposals (including Kyoto, a tax in all but name) represent bad value for money, and that the fourth is not developed enough to judge - is beyond me.