Hoogwijk performed a study on potentials of renewable energy sources, including an assessment of the increase in land use for the built environ­ment [3]. Current land use for the built environment was estimated to be 2% of the total global land mass excluding Antarctica. United Nations projections estimate this land use to be 4% in 2030 [19].

We therefore assume that land use for the built environment will in­crease from the current 2% to 4% in 2030. We extrapolated this figure, using the population growth numbers used throughout the Ecofys Energy Scenario, to a 5% land use in 2050. The growth from current to 2050 land use for the built environment therefore requires excluding 3% of global land mass, excluding Antarctica, for this purpose.

Next, we have assumed that all of this expansion will take place on unprotected grass — and woodland because expansion into other land types is either not possible, not acceptable or much less likely. 3% of the global land mass, excluding Antarctica, amounts to 12% of the unprotected grass and woodland. We have therefore reduced the land potential for rain-fed cultivation of energy crops by 12% for human development.

The reduction then totals 1,040,000 km2 (104 million hectares). This reduction is additional to the exclusion of urban areas based on IIASA data.