P. C. Smith

Advances in large‐scale crop modeling

Intensified human activity and a growing population have changed the climate and the land biosphere. One of the most widely recognized human perturbations is the emission of carbon dioxide (C02) by fossil fuel burning and land-use change. As the terrestrial biosphere is an active player in the global carbon cycle, changes in land use feed back to the climate of the Earth through regulation of the content of atmospheric CO2, the most important greenhouse gas,and changing albedo (e.g., energy partitioning). Recently, the climate modeling community has started to develop more complex Earthsystem models that include marine and terrestrial biogeochemical processes in addition to the representation of atmospheric and oceanic circulation. However, most terrestrial biosphere models simulate only natural, or so-called potential, vegetation and do not account for managed ecosystems such as croplands and pastures, which make up nearly one-third of the Earths land surface.

Rising food demand, climate change and the use of land and water

Some of the most important interactions between human society and the environment occur in the agricultural sector. Agricultural production is – more than most other economic activities – affected by socio-economic and environmental conditions. Human demand for food effectively drives production and land use patterns. With respect to climate, agriculture acts as a source and a sink of greenhouse gases at the same time. The complex linkages between food production, land use and climate change can only be understood in a long-term, interdisciplinary framework. However, there is still a lack of consistent modelling approaches which take spatial variations of environmental conditions into account and represent biophysical as well as socio-economic driving forces over several decades into the future. From an economic perspective, the importance of agriculture varies according to the level of economic development. In poor countries, agricultural and food production contributes a major share to GDP and is an important source of employment and household income. Many economists claim that there is no way out of poverty, except through agricultural and rural development (McCalla, 1999). In the process of economic development, the role of agriculture is decreasing, and in rich industrialised countries the share of agriculture in GDP and overall labour force is now below 5%. These trends occur despite wideranging government interventions to achieve the contrary. Like most economic sectors, agriculture is also strongly affected by macroeconomic conditions, lifestyles changes and consumption patterns. From an environmental point of view, agriculture is of key importance in rich and poor countries, regardless of the level of economic development. On a global scale, agricultural production accounts for about 40% of total land use, and about 70% of all freshwater withdrawals. It also affects important nutrient cycles, contributes significantly to climate change through emissions of methane and nitrous oxide, and it is considered one of the most important causes for