Climate mitigation and the future of tropical landscapes

Abstract

Land-use change to meet 21st-century demands for food, fuel, and fiber will depend on many interactive factors, including global policies limiting anthropogenic climate change and realized improvements in agricultural productivity. Climate-change mitigation policies will alter the decision-making environment for land management, and changes in agricultural productivity will influence cultivated land expansion. We explore to what extent future increases in agricultural productivity might offset conversion of tropical forest lands to crop lands under a climate mitigation policy and a contrasting no-policy scenario in a global integrated assessment model. The Global Change Assessment Model is applied here to simulate a mitigation policy that stabilizes radiative forcing at 4.5 W m(-2) (approximately 526 ppm CO(2)) in the year 2100 by introducing a price for all greenhouse gas emissions, including those from land use. These scenarios are simulated with several cases of future agricultural productivity growth rates and the results downscaled to produce gridded maps of potential land-use change. We find that tropical forests are preserved near their present-day extent, and bioenergy crops emerge as an effective mitigation option, only in cases in which a climate mitigation policy that includes an economic price for land-use emissions is in place, and in which agricultural productivity growth continues throughout the century. We find that idealized land-use emissions price assumptions are most effective at limiting deforestation, even when cropland area must increase to meet future food demand. These findings emphasize the importance of accounting for feedbacks from land-use change emissions in global climate change mitigation strategies.

Fig. 1.

Net CO₂ emissions from global land use change under GCAM reference and RCP4.5 scenarios with different levels of agricultural productivity assumed.

Fig. 2.

Tropical land use change as fraction of grid-cell area in 2100 minus fraction of grid-cell area in 2005 for (A) cropland (including bioenergy crops) under the RCP4.5 case, (B) forest lands under the RCP4.5 case, (C) cropland (including bioenergy crops) under the zAPGref case, and (D) forest lands under the zAPGref case.

Fig. 3.

Bioenergy use in the GCAM scenarios from (A) dedicated bioenergy crops and (B) crop and forestry residues and municipal solid waste.

Fig. 4.

Changes in (A) cost of corn production and (B) index of food expenditure as a fraction of GDP, indexed to 2005 values.