There is a new role for global climate policy and the Intergovernmental Panel on Climate Change (IPCC) to support national implementation. For keeping within global ecological limits, public debate has shifted from concerns about the reliability of model-based climate projections to national legislators considering questions of when, where, and how to modify longer term trends. However, modeling remains the essential scientific tool by which the climate problem is defined assuming that society and the economy can be transformed, actually re-engineered, with relative ease. Inputs from the IPCC to the new governance process, the global ‘stocktake’, suggesting solutions will now influence deliberations between stakeholders, national actions and global cooperation. How best to shape a different science architecture and agenda linking science with both policy and society requires, for example, giving as much importance to reports of multilateral bodies and business consultancies as to peer-reviewed literature. This paper lays out some ideas how legitimacy can be maintained even as the IPCC recommends policy options and not just advice that is policy relevant.