Tetra-stable bifurcation structure of the climate system of Earth: mechanisms triggering potential transition to the greenhouse steady state

The emissions of human-made greenhouse gases may trigger transition from the pre-industrial climate to the greenhouse steady state, which was for the last time abandoned 49 million years ago. The study provides an energy balance climate model with temperature-dependent parameters, which illustrates the tetra-stable bifurcation structure of the climate system. Bifurcation structures can evolve in time leading to climate variability and only strong changes may trigger climate transitions between steady states. The potential tipping point triggering irreversible climate transition to the greenhouse steady state is estimated as 291.7 K (577 ppmv CO2). Event-tipping is revealed as the mechanism of this unwanted climate transition. The newly attained greenhouse steady state would be self-sustained mainly due to permanent biomass methane fermentation. Therefore, the minimisation of methane release from biomass methane fermentation, permafrost melting, and clathrates decomposition is suggested as the important climate change mitigation strategy.