Climate Resilience under Zero-Emission Commitment Scenarios

• Applicant: Professor Dr. Niklas Boers
• Subject Area: Oceanography ; Atmospheric Science
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 551886647

Concerns have been raised that several subsystems of the Earth system may lose resilience under ongoing global warming. Even if greenhouse gas emissions are reduced to net-zero in the coming decades, the impacts of past emissions will play out on longer time scales and keep affecting key climate subsystems. Moreover, rapid reductions in greenhouse gas emissions to reach net-zero may lead to highly non-trivial responses, for example, abrupt collapse or recovery of the Atlantic Meridional Overturning circulation, depending on the specific global warming level at which net-zero emissions are reached. Given the potential for significant impacts of large-scale resilience loss even under net-zero emission commitments, an in-depth investigation is urgently needed. We will investigate global climate resilience under different zero-emission commitment (ZEC) scenarios, combining large-ensemble simulations of the comprehensive Earth System model CESM2 with theoretical approaches to quantify resilience. We will focus our assessment of climatic impacts of ZEC scenarios on the Atlantic Ocean circulation, tropical rainforests including the Amazon, and the global monsoon systems. Based on dynamical system theory, we will quantify the resilience of these subsystems under different zero-emission scenarios and identify global warming thresholds conducive to maintaining their resilience. The planned large ensembles will facilitate a thorough investigation of associated uncertainties, crucial for reliably identifying safe operating spaces. Following a comprehensive analysis of the global-scale impacts of zero-emission scenarios at different global warming levels, we will conduct in-depth analyses of the physical mechanisms underlying long-term Atlantic Ocean circulation variability, including collapse and recovery of the Atlantic Meridional Overturning Circulation (AMOC). In particular, the AMOC’s stability is known to be influenced by internal atmospheric variability as well as net freshwater flux to the Atlantic Ocean. The large ensembles will help us to understand expected diverging AMOC behavior across ensemble members for scenarios with net Atlantic Ocean freshwater import close to a critical value. To reach our objectives, we will combine our new ensemble of ZEC simulations, with theoretical investigations of stability and resilience changes of major Earth system components. We will adapt stability and resilience notions developed for low-dimensional dynamical systems in the context of bifurcations to complex climate phenomena. These theory-guided approaches will be complemented by data-driven approaches based on Deep Learning and Explainable Artificial Intelligence for anticipating resilience loss and resulting regime shifts. We will use the CESM2 simulations to identify optimal precursor indicators for potential AMOC collapse, which will then be applied to observational data.

• DFG Programme: Research Grants
• International Connection: South Korea
• Cooperation Partner: Professor Jong-Seong Kug