Assessment of Feedbacks in the Earth System under Anthropogenic Forcing : Two Case Studies
Feedbacks determine the sensitivity of the Earth system to perturbations. In the last centuries, the Earth system has been undergoing substantial changes caused to a great extent from the human activity. Nowadays, it is well documented that global warming is mainly driven by the anthropogenic emissions of greenhouse gases. In the future, these emissions will likely continue and lead to further climate warming. Large-scale climate engineering projects are human actions proposed to counteract climate warming. However, these projects could also cause unintentionally perturbations to the Earth system or its subsystems. Scientists apply models to estimate the impact of these anthropogenic forcings on the Earth system in future projections. Therefore it is important that feedbacks are well represented in these models to make reliable predictions. The aim of this PhD thesis is to advance the research in feedbacks and their response to anthropogenic forcing in the Earth system or its subsystems. Two case studies are carried out with a focus on a) the atmospheric feedbacks in North Africa driven by an irrigated afforested Sahara, and b) the biogeochemical feedbacks related to the phosphorus cycle and its link to oceanic deoxygenation. This PhD thesis advances the understanding of the North African climate system and their feedbacks under an artificial large-scale afforestation scenario. It reveals the potential and unintentional side effects of such a climate engineering project. Furthermore, this thesis discusses to what extent human activity could drive the global ocean suboxic or anoxic and reassessed the relevance of the different feedbacks for the deoxygenation of the ocean.