Anthropocene Climate Bifurcation

• Main Authors: Kypke, Kolja Leon, Langford, William Finlay, Willms, Allan Richard
• Format: Text
• Language: English
• Published: 2020
• Subjects: Antarctic; Arctic; The Antarctic; albedo; Antarc*; Climate change
• Online Access: https://doi.org/10.5194/npg-2020-4; https://www.nonlin-processes-geophys-discuss.net/npg-2020-4/

This article presents the results of a bifurcation analysis of a simple Energy Balance Model (EBM) for the future climate of the Earth. The main focus is on the question: Can the nonlinear processes intrinsic to atmospheric physics, including natural positive feedback mechanisms, cause a mathematical bifurcation of the climate state, as a consequence of continued anthropogenic forcing by rising greenhouse gas emissions? Our analysis shows that such a bifurcation could cause an abrupt change, to a drastically different climate state in the EBM, warmer and more equable than any climate existing on Earth since the Pliocene Epoch. In previous papers, with this EBM adapted to paleoclimate conditions, it was shown to exhibit saddlenode and cusp bifurcations. The EBM was validated by the agreement of its predicted bifurcations with the abrupt climate changes that are known to have occurred in the paleoclimate record, in the Antarctic at the Eocene-Oligocene Transition (EOT) and in the Arctic at the Pliocene-Paleocene Transition (PPT). In this paper, the EBM is adapted to fit Anthropocene climate conditions, with emphasis on the Arctic and Antarctic climates. The four Representative Concentration Pathways (RCP) developed by the IPCC are used to model future CO 2 concentrations, corresponding to different scenarios of anthropogenic activity. In addition, the EBM investigates four naturally occurring nonlinear feedback processes which magnify the warming that would be caused by anthropogenic CO 2 emissions alone. These four feedback mechanisms are: ice-albedo feedback, water vapour feedback, ocean heat transport feedback and atmospheric heat transport feedback. The EBM predicts that a bifurcation resulting in a catastrophic climate change will occur in coming centuries, for an RPC with unabated anthropogenic forcing, amplified by these positive feedbacks. However, the EBM suggests that appropriate reductions in carbon emissions may limit climate change to a more tolerable continuation of what is observed today. This EBM has an Equilibrium Climate Sensitivity (ECS) near the high end of the range recorded by the IPCC.