Carbon implications of converting cropland to bioenergy crops or forest for climate mitigation: a global assessment

Abstract

The potential for climate change mitigation by bioenergy crops and terrestrial carbon sinks has been the object of intensive research in the past decade. There has been much debate about whether energy crops used to offset fossil fuel use, or carbon sequestration in forests, would provide the best climate mitigation benefit. Most current food cropland is unlikely to be used for bioenergy, but in many regions of the world, a proportion of cropland is being abandoned, particularly marginal croplands, and some of this land is now being used for bioenergy. In this study, we assess the consequences of land-use change on cropland. We first identify areas where cropland is so productive that it may never be converted and assess the potential of the remaining cropland to mitigate climate change by identifying which alternative land use provides the best climate benefit: C 4 grass bioenergy crops, coppiced woody energy crops or allowing forest regrowth to create a carbon sink. We do not present this as a scenario of land-use change -we simply assess the best option in any given global location should a land-use change occur. To do this, we use global biomass potential studies based on food crop productivity, forest inventory data and dynamic global vegetation models to provide, for the first time, a global comparison of the climate change implications of either deploying bioenergy crops or allowing forest regeneration on current crop land, over a period of 20 years starting in the nominal year of 2000 AD. Globally, the extent of cropland on which conversion to energy crops or forest would result in a net carbon loss, and therefore likely always to remain as cropland, was estimated to be about 420.1 Mha, or 35.6% of the total cropland in Africa, 40.3% in Asia and Russia Federation, 30.8% in Europe-25, 48.4% in North America, 13.7% in South America and 58.5% in Oceania. Fast growing C 4 grasses such as Miscanthus and switch-grass cultivars are the bioenergy feedstock with the highest climate mitigation potential. Fast growing C 4 grasses such as Miscanthus and switch-grass cultivars provide the best climate mitigation option on %485 Mha of cropland worldwide with~42% of this land characterized by a terrain slope equal or above 20%. If that land-use change did occur, it would displace %58.1 Pg fossil fuel C equivalent (C eq oil). Woody energy crops such as poplar, willow and Eucalyptus species would be the best option on only 2.4% (%26.3 Mha) of current cropland, and if this land-use change occurred, it would displace %0.9 Pg C eq oil. Allowing cropland to revert to forest would be the best climate mitigation option on %17% of current cropland (%184.5 Mha), and if this land-use change occurred, it would sequester %5.8 Pg C in biomass in the 20-year-old forest and %2.7 Pg C in soil. This study is spatially explicit, so also serves to identify the regional differences in the efficacy of different climate mitigation options, informing policymakers developing regionally or nationally appropriate mitigation actions.

Major limitations to achieving “4 per 1000” increases in soil organic carbon stock in temperate regions: Evidence from long‐term experiments at Rothamsted Research, United Kingdom

“…There are obviously severe limitations to the area of land that can be removed from agriculture globally if food security goals are to be met. But, in limited situations where soils are either of low productivity or are fragile and prone to erosion, conversion from agriculture to forest or grassland may be a logical strategy (Albanito et al., ; Smith et al., ). A good example is the “grain for green” programme in China that reduced soil erosion and led to considerable increases in SOC (Chadwick et al., ; Song, Peng, Zhou, Jiang, & Wang, 2014).…”

Protein futures for Western Europe: potential land use and climate impacts in 2050

“…It could be used to sequester carbon through forest plantation or by producing biofuels to displace fossil fuels (Albanito et al 2015). Alternatively, it could be used to produce more food (or biomass for nonfood purposes) for export, potentially sparing agricultural land or reducing deforestation pressures overseas.…”

“…To establish, how much would require more detailed climate modelling than the GWP we used here. While forest planting on low-quality agricultural land could be an important short-term mitigation strategy, its merits need to be weighed against other land use options (Albanito et al 2015), which are not considered here.…”

Mitigation potential and environmental impact of centralized versus distributed BECCS with domestic biomass production in Great Britain

“…The LUC of agricultural land to bioenergy production has the potential to provide significant GHG emission savings and soil carbon sequestration (Albanito et al, ). We show that if all the marginal agricultural land within the catchment areas of the power stations is converted to bioenergy production, the net reduction in soil GHG emissions from LUC range from 9 to 11 /year in the centralized and distributed system.…”