Estimating changes in global vegetation cover (1850–2100) for use in climate models

[1] Historical changes in global cropland area based on estimates of Ramankutty and Foley (1999), and projections of future changes under IPCC SRES development scenarios taken from the IMAGE 2 model, were combined with a simple classification of present-day satellite data. These data were used to estimate annual changes in area fractions occupied by primary plant functional types (PFTs) between 1850 and 2100 using two different approaches. The linear interpolation approach assumed that natural vegetation area varies in inverse proportion to cropland area. The rule-based approach added simple transition rules to define the sequence by which natural PFTs are converted to agriculture (e.g., grassland before forest) and by which abandoned cropland reverts to natural vegetation. In both approaches, constraints were imposed to ensure the simulated PFT composition was consistent with available information. The resulting time series data can be used in coupled biosphere-atmosphere models, and in uncoupled global climate models, to represent time-varying land cover.