Towards a Great Land-Use Transformation?

Climate change poses great threats to many compartments of the Earth System and, as a consequence, to human societies. There is growing scientific evidence that a rise of the global mean temperature by more than 2 °C (as compared to pre-industrial levels) would irreversibly harm many ecosystems and most likely exceed the adaptive capacities of many societies. In order to confine global warming to maximally 2 °C, major efforts to reduce emissions of greenhouse gases are required. These may even include ‘negative emissions’ of carbon dioxide to be achieved by the second half of this century: carbon dioxide may have to be actively removed from the atmosphere and deposited on land for many decades, centuries, or even millennia. The transformation of the energy system, steering away from fossil fuels, will have to contribute the lion’s share of emission reductions. However, land-use changes are currently responsible for one third of total greenhouse gas emissions, so improved land management and productivity increases on land under cultivation could significantly contribute to climate change mitigation since soils and forests store large amounts of carbon. Several techniques that would allow for negative emissions are currently discussed: afforestation and the restoration of peat and wetlands would be the most easily accessible options. Other options such as technologies for carbon capture and storage (CCS) in the energy sector involve sequestration of carbon dioxide in geological formations underground. Carbon dioxide could be directly extracted from the atmosphere making use of chemical reactions turning the greenhouse gas into solid carbonates. The large-scale application of these technologies is however still in its infancy. The most promising mechanism to achieve negative emissions is to fuel power plants with biomass, extract carbon dioxide from the exhaust and sequester it underground. However, in order to draw down a really significant amount of carbon dioxide, enormous quantities of biomass would have to be processed this way.