The climate impact of land use change in the miombo region of south central Africa

Abstract

The African woodlands known as miombo are one of the world’s largest currently relatively unexploited, but potentially arable, land resources. Miombo landscapes one of the top contemporary locations of conversion of dry forests to crop agriculture. This study investigates the net effect on climate forcing that results from different types of land use change in miombo, taking into account the multiple mechanisms through which the land interacts with the climate system, locally and globally. It finds that when miombo is converted tointensively cultivated commercial crops, the landscape-averaged 30-year net greenhouse gas forcing relative to intact woodlands is 309gCO2e m-2 y-1, of which net emission of carbon dioxide amount to 66%, non-CO2 greenhouse gas effects to 33%, plus unquantified contributions from ozone precursors and aerosols. We find that net brightening of the land surface resulting from clearing the woodlands generates a cooling effect larger than the greenhouse gas forcing (-1139gCO2e m-2 y-1). Greenhouse gas forcings resulting from transformation to extensive subsistence agriculture that are 78% lower than those from the intensive commercial agriculture path, and 40% lower if a transformation which sets out to mimic ecological processes in the miombo landscape is undertaken. Once the effect of surface brightening is included, then the total forcing for extensive subsistence agriculture is -834gCO2e m-2 y-1 , about the same as intensive commercial, and eco-agriculture is -102gCO2e m-2 y-1 . Taking into account the account the larger areas required for to achieve the same production, intensive commercial agriculture is the more climate-protective option.Keywords: greenhouse gas, net radiation, deforestation.