Impacts of Future Bioenergy on Global Land Use Change and the Climate

Bioenergy is expected to play a key role in the global energy mix over the next century. This is due to its potential for providing energy security and the advantages it has as a land-based mitigation strategy.

However, there are large uncertainties with regards to deployment levels of bioenergy and its impact on the land system. Bioenergy deployment could potentially reach around 324 EJ/year by 2100 which could correspond to an increase of up to 550 million ha of cropland used for second generation energy crops, equivalent to 35% of current total cropland. The introduction of another large land use sector could further accelerate deforestation and biodiversity loss, and may in fact increase GHGs. It is therefore important to assess the impacts that large-scale energy crop cultivation could have on global land use change (LUC), the emissions it produces from deforestation and its impact on climate change.

Figure 1 Schematic diagram of biogeochemical and biogeophysical effects of land use change for bioenergy crop plantations and the impacts of these effects on near surface air temperature (TNS).

In order to do this, an analysis of spatially-explicit future mitigation scenarios that include LUC for bioenergy and have a climate target is needed. By inputting these scenarios into climate models, it can be determined how exactly the LUC in these scenarios impacts the climate by analysing both the biogeochemical (the CO2 radiative warming from land use CO2 emissions) and biogeophysical (land-surface changes from agriculture and pasture affecting surface albedo, roughness, and energy balance) components of temperature change.

A number of previous studies indicate that overall, global LUC has a negligible impact on the Earth’s energy budget and surface air temperature (SAT). This is mainly due to the fact that the BGC and BGP impacts of LUC on the global mean surface air temperature counteract each other. The BGC impact of LUC tends to lead to a global warming due to increased GHG concentrations, however the BGP impact leads to a cooling at the global scale, caused by an overall increase in the surface albedo as forests are replaced with cropland.

Although the impact of LUC on climate can be negligible on a global scale, studies assessing the impact of global bioenergy on LUC have shown that it can be pronounced over the land in the temperate and high northern latitudes (extratropical regions). Here it has been seen that, when forest is converted to cropland, a cooling due to an increase in land surface albedo offsets the warming due to land-use CO2 emissions produced from tropical deforestation. On the other hand, warming effects from a decrease in albedo have shown to offset cooling effects from increase in evapotranspiration when desert or arable land is replaced with energy crops.

Some studies have shown that the warming that occurs in the mid- to high-latitudes from BGC processes is not always located in regions occupied by biofuel plantations. This is due to the fact that GHG emissions produced from land clearing or deforestation (CO2) and fertilisation of energy crops (N2O) are well mixed in the atmosphere at the global scale. It is also because GHG-induced warming reduces the snow cover in these regions which changes surface albedo, causing polar amplification of the global warming from enhanced GHG emissions. Figure 1 (above) displays these BGC and BGP interactions and their impact on near surface air temperature TNS .

Although previous studies have looked at BGC and BGP climate impacts of LUC for bioenergy, they either focus on BGC effects on climate or, when including BGP effects on climate, only observe specific regions of the globe. This project will thus be carrying out a global assessment of BGP impacts (and to a lesser extent BGC impacts) of bioenergy production on LUC over the next century by analysing spatially-explicit future mitigation scenarios from the MAgPIE (Model of Agricultural Production and its Impact on the Environment) integrated assessment model and inputting these scenarios into the University of Victoria (UVic) climate model.

Charlotte Weaver is reading for EPSRC and UBoC CASE funded PhD on the impacts of bioenergy on land use change and climate.