A stable hothouse triggered by a tipping mechanism

The climate system's nonlinear dynamics is influenced by various external forcings and internal feedbacks, which can give rise to regional and even global tipping points that may lead to significant, potentially irreversible changes. Palaeoclimatic records reveal that Earth's climate has shifted between distinct equilibria, including a 'hothouse Earth' state with temperatures about 10 K higher than at present. However, a specific mechanism for a sudden tipping to an alternate stable state, several degrees warmer than the present climate, has yet to be presented. We introduce a temperature-carbon-vegetation (TCV) model comprising an energy balance model (EBM) of global temperature, coupled with global terrestrial and ocean CO2 dynamics, and with vegetation ecosystem change. Our model exhibits a new tipping mechanism that leads to a hothouse Earth under a high-emission scenario. Its simulations align with both observations and Intergovernmental Panel on Climate Change (IPCC)-class global climate models (GCMs) prior to tipping. The two processes that produce global tipping are: (i) temperature-albedo feedback owing to darkening of the terrestrial cryosphere by glacial microalgae and (ii) limits to vegetation adaptation that lead to reduced carbon absorption. This article is part of the theme issue 'Critical transitions and intelligent control in complex systems'.