by Chieh-Hsin Chen
According to various economic and environmental estimations, it is highly possible that future global energy demand will increase up to 250% by 2050, which will be impossible to achieve using current available natural fuel sources. Biofuels have been proposed as a potential low-carbon energy source that may help assist in meeting energy demands; as well as improving greenhouse gas emission problem from fossil fuel combustion. Hallgren et al. (2013) used various assessment models that link an economic model with climate, biogeochemistry, and biogeophysics models to examine the effects of possible land use changes from an expanded biofuel program over the first half of 21st century. Surprisingly, the results of this modeling effort show that overall, the biogeochemical and biogeophysical impacts are negligible from a global perspective; the models do show regional patterns of climate change in certain areas such as Amazon Basin and parts of Congo Basin. Considering the amount of land conversion that will be needed there will no doubt follow considerable debate about the accuracy of this conclusion. We would welcome your comments below, but more explanation follows.
With the rising popularity of biofuel, the need for biofuel crop expansion is also increasing. Global biofuel programs will put pressure on the land supply and results in widespread transformation in land use. To understand the impact of land use change on different kinds of land areas, the authors gather information from multiple studies and examined the impact of global climate and greenhouse gas emission with assessment models. The authors focus on two aspects of the impact: biogeochemistry and biogeophysics. Biogeochemistry evaluates the change in process of plant functions such as photosynthesis, respiration, decomposition, nitrification, and denitrification; the assessment pinpoint on the flux of two-greenhouse gases CO2 and N2O. Biogeophysics evaluates the change in albedo and evapotranspiration from different types of vegetation. Albedo is surface reflectivity and evapotranspiration is the combination of evaporation through plants to atmosphere. Climate change can be closely impacted by both biogeochemistry and biogeophysics.
The models were set up with sets of simulations and limitations; and the simulations are accumulating from both global climate responses as well as local responses. The results of climate change are evaluated mainly through change in atmospheric greenhouse gas concentration, surface albedo, local hydrological cycle, and atmospheric circulations. The experiment is designed to consist of an 80-years- equilibrium climate model simulation for the year 2050; and there are two cases of experimental manipulation of the equilibrium model. Case 1 makes all land available for biofuel crop use or managed use for alternative agriculture; case 2 limited access to unmanaged land with the limits based on the recent history of regional land conversion rate.
The results show that at the global scale, the expansion of biofuel policy and the associated land use change has a negligible impact on the global climate due to the fact that biogeochemical and biogeophysical impacts of biofuel compensate each other. The biogeochemical impacts lead to a global warming with an increase in greenhouse gas emission to atmosphere; however, the carbon emission reduction from using biofuel instead of fossil fuel is not incorporated into the model so the impact would be even smaller. Biogeophysical impacts lead to a cooling at the global scale, caused by an overall increase in albedo as forest is replaced by cropland. The warming from biogeochemical impacts and the cooling from biogeophysical impacts compensate each other. Based on this study, biofuel expansion will not have large impact on climate globally, but it is suggested that in tropical forest regions, the change of land use and deforestation would cause regional climate change.
Hallgren, W., Schlosser, CA., Monier, E., Kicklighter, D., Sokolov, A., Melilo, J, 2013. Climate Impact of a Large-Scale Biofuel Expansion. Geophysical Research Letter 40, 1624−1630. http://bit.ly/1tWkasp