All countries need to recognize their responsibilities in meeting this long-term goal, but we seek leadership from the G8 to agree to deep cuts by 2050. Leaders of major developing economies will also have to set out their plans to achieve emissions mitigation consistent with sustainable economic development, including, ultimately, absolute cuts that could take effect on a delayed basis.

For the sake of credibility, a realistic intermediate milestone should also be established to provide a marker on progress toward the long-term commitment. IPCC analysis suggests that, depending on the emissions growth scenario used, an intermediate milestone in the range of a 14-35 percent reduction in global emissions by 2030 against current levels could be achievable at a carbon price of $ 20/ton CO2-equivalent.

Undertaking a bottom-up quantification of the overall potential for an intermediate emissions reduction milestone would, we believe, be a useful and practical exercise for the international business community and governments to engage in over the next several months.

Such an exercise would encourage a joint focus on where realistic abatement potentials can be found in the short to medium term. It would also provoke a practical public-private dialogue on how the framework can best be designed to ensure that these abatement potentials will likely be achieved.

A number of other bottom-up pieces of the architecture also have the potential to improve the environmental effectiveness, economic efficiency and political acceptability of a post-Kyoto framework.

These, too, will need to be constructed through much closer collaboration with private sector and other non-governmental experts than is common in intergovernmental negotiations.

In our report to G8 leaders, we recommend public-private strategies to spur technology development and diffusion, encourage benchmarking and other arrangements among firms in the same industrial sector, leverage private investment and facilitate technology transfer in developing countries, empower consumers with better information about the implications of their choices, and create common metrics to improve the efficiency of carbon markets and enable apples-to-apples comparisons of investor risks, corporate strategies, and the performance of countries against targets.