Abstract
The land area of the Earth greatly influences climate dynamics through biogeophysical and biogeochemical processes. These processes concern, respectively, the exchange of energy and water, and the exchange of greenhouse gasses (GHGs) such as CO2, CH4 and N2O, between land systems and the atmosphere. By using the Earth’s land surface,
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humans have greatly altered it – leading to significant environmental impacts. Historically, climate change has mostly been caused by fossil fuel combustion. Land use, land-use change and forestry (LULUCF) have caused an estimated 34% of cumulative anthropogenic CO¬2 emissions since 1750. At the same time, agriculture is responsible for about 13% of global GHG emissions in the form of non-CO2 GHG emissions. The importance of land and land use in climate dynamics means that land has a role in preventing dangerous climate change. First, it is essential to significantly reduce the 23% of annual GHG emissions from the agriculture, forestry and other land use (AFOLU) sector to make ambitious climate targets feasible. Second, land is key to various techniques to remove carbon from the atmosphere (so-called negative emissions or carbon dioxide removal (CDR)). In this thesis, a large portfolio of land-based mitigation measures is assessed in the context of different land-use futures. In addition, detailed analysis are provided on two key land-based mitigation measures: afforestation, and peatland protection and restoration. In addition to climate, land is central to many other sustainable development issues and environmental challenges. For example, it is essential for the provision of resources such as food, energy and water, as well as to sustain terrestrial biodiversity, as also recognized in the Sustainable Development Goals and the planetary boundaries. A useful approach to study different dimensions of sustainable development and environmental change is the nexus concept which recognizes that components of a system are inherently interconnected and must be investigated and managed in an integrated, holistic manner. In this thesis, the water-land-energy-food-climate (WLEFC) nexus is addressed, taking into account trade-offs and synergies between these different systems in achieving multiple goals. Scenario analysis can be used to explore the role of land use in climate change and climate change mitigation, and for other societal goals related to the WLEFC nexus. An important ambition of the scientific community is to develop scenarios that achieve both climate and other environmental and sustainability goals such as the PBs and the SDGs. In this thesis, we use exploratory scenarios that investigate how the future might develop under pre-defined assumptions, as well as normative scenarios that aim for pre-defined targets and describe pathways that could achieve these goals. Examples of targets are stabilizing global warming, nature protection or limits to water extraction. These scenarios are developed using the IMAGE integrated assessment model framework.
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