Predicting land-surface climates-better skill or moving targets?

Uncertainty in the prediction of continental surface climates is identified by the Intergovernmental Panel on Climate Change (IPCC) as limiting our confidence in projecting future climates. To reduce this uncertainty, the Atmospheric Model Intercomparison Project (AMIP) Diagnostic Subproject 12 (DSP 12) and the Project for Intercomparison of Land-surface Parameterisation Schemes (PILPS) have used a substantially improved experimental design, coupled with a greater variety of land-surface schemes (LSSs) represented in AMIP II, to investigate whether the thirty years of effort in land surface modelling has led to improvements in simulations of continental surface processes. In AMIP II, we find a clear chronological sequence of: First generation 'no canopy'; second generation 'SiBlings'; and 'recent schemes'. We conclude that three decades have improved continental surface modelling capability but that full confidence in our ability to project land-surface quantities using climate models remains elusive, in part due to uncertainties in surface observations.