Climate and crop interactions : the biogeophysical effects on climate and vegetation

The interactions between changing agricultural land and climate are multi faceted and only partially understood. This thesis looks at interactions between crops and climate from assumptions about parameterisations that underpin crop changes in models; the unintended consequences of policies which affect land cover; and the impacts of deliberate crop changes (e.g. biogeoengineering). Focusing on the biogeophysical effects (from albedo, evapotranspiration etc.) these effects are compared to the biogeochemical effects (from greenhouse gases). There are considerable local and global biogeophysical effects to climate from land-use change, which do not necessarily scale linearly with the amount of landuse change itself. Changing the parameterisation of contributory factors to biogeophysical changes can affect the climate at least as much as deliberate alterations. Similarly, climate forced land cover change effects can be larger than land use forced changes. Increases in crop yield from deliberately altered albedo are small, but the changes to climate via albedo from different assumptions of yield are significant at a global and regional scale. This work emphasises the importance of including biogeophysical interactions in assessments of crop and land cover change in policy decisions, but also that the effects of land use change should not be overestimated, as the net effects are often smaller than the parameter uncertainty.