Objectives of this Grand Challenge include the active involvement of the relevant observational communities in establishing benchmark data sets, and of the corresponding modelling communities in undertaking detailed evaluations and analyses. The outcomes will be peer-reviewed, community-led papers summarizing the state of knowledge, and clearly articulating areas in which confident statements can be made, as well as those for which major uncertainties remain. By engaging the international community, and building upon the scientific network WCRP has established over time, efficient and effective progress can be made with only modest investment (primarily funds to bring people together and sustain ongoing communication and collaboration).

The community papers that arise from this work will serve two distinct purposes: 1) to draw attention to knowledge gaps that could serve as foci for national and international funding opportunities, and 2) to consolidate current understanding and develop improved modelling capabilities that will be brought to bear in climate change projections underpinning the IPCC and other assessment reports, and thereby the global policy-development arena.