Climate impacts due to albedo change in LCA of agricultural systems

Abstract: Agricultural systems for production of food, energy and materials are a major driver of climate change, due to land use and greenhouse gas (GHG) emissions along the supply chain. Crop cultivation also affects the climate by changing land surface albedo, i.e. the fraction of solar radiation reflected back from the ground. Increased albedo could counteract the radiative forcing and warming effect of emitted GHGs.This thesis examined how individual crops and cultivation practices in Sweden influence albedo, and thus the climate. Field measurements and satellite data were used to analyse differences between crops, management practices and environmental conditions. Methods for assessing climate impacts due to albedo change and for comparing these impacts with those of GHGs were developed. Time-dependent life cycle assessment (LCA) was performed to obtain a perspective on the importance of albedo change for the climate impact of crop and bioenergy production, relative to life-cycle GHG emissions and carbon sequestration.The results showed higher albedo for soil kept covered year-round, e.g. by perennial crops or winter varieties and by straw left in the field, combined with delayed or reduced tillage. In case studies, albedo increased by 31% under willow and 6-11% under different food or feed crops relative to unused land. This albedo increase countered the effect of GHG emissions from manufacture of inputs and fuel consumption, by 20-60% when measured as GWP100 and by 60-200% as GWP20. Impacts assessed as global mean temperature change (ΔT) over time were dominated by albedo-induced cooling on short time scales and by the effects of emitted GHGs and carbon sequestration on longer time scales. The local, immediate effect of increased albedo could be exploited in strategies to dampen warming locally and alleviate heat stress in summer.