Soutenance de thèse : Thomas bossy

PhD defense: Thomas Bossy

Impact-defined climate targets: estimating ensembles of pathways of compatible anthropogenic drivers through inversion of the cause-effect chain

Thomas Bossy, sous la direction de Philippe Ciais (LSCE) et Philippe Bousquet (LSCE)

2 octobre

À 14h au CIRED
et en ligne


This dissertation presents a multidisciplinary approach to climate change research. It explores the limitations of the current scenario-building framework used
by the Intergovernmental Panel on Climate Change (IPCC) and presents new strategies for better understanding climate futures. Using Pathfinder, a simple model focused on climate and the carbon cycle, this research fills a gap in the range of existing simple climate models by incorporating the latest data and providing a backward, temperature-driven examination of climate change scenarios. Prospects for improvement are then identified by discussing the representation of the ocean in Pathfinder, focusing on the Ocean Heat-Carbon Nexus and its critical role in the global carbon cycle and the response of Earth’s climate to cumulative CO2 emissions. A comparison is made between the representations of the Ocean Heat-Carbon Nexus in Pathfinder and state-of-the-art Earth system models, highlighting the significant discrepancies and potential implications for future warming scenarios. After introducing Pathfinder, my research first examines the CO2 emission reductions physically required to meet the 1.5C global warming target, emphasizing the importance of CO2 emissions from land use and non-CO2 forcing. We then reverse the causal chain to link environmental impacts to anthropogenic activities, which is a unique approach. The study maps the spaces of anthropogenic activities compatible with planetary boundaries and introduces a modeling framework that accounts for global warming, ocean acidification, sea level rise, and Arctic sea ice melt. Furthermore, this thesis examines the role of Integrated Assessment Models (IAMs) in understanding the costs associated with these climate scenarios. It explores the impact of conceptual choices in these models on the identification of robust mitigation pathways and examines the effects of physical uncertainty and intergenerational equity. This manuscript concludes with an appreciation of the key contributions of my doctoral research to climate change modeling, exploration of new frontiers and opportunities in the field, and personal insights into the research journey. Overall, this research represents a unique, innovative approach to climate change modeling that will hopefully provide practical tools for assessing and developing mitigation strategies.

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