Committed terrestrial ecosystem changes due to climate change

Some aspects of the Earth system—such as global mean temperatures, and sea-level rise due to thermal expansion or melting of large ice sheets—continue to respond to climate change long after the stabilization of radiative forcing. Simulations with a coupled climate–vegetation model show that similarly ecosystems may be committed to significant change after climate stabilization. Targets for stabilizing climate change are often based on considerations of the impacts of different levels of global warming, usually assessing the time of reaching a particular level of warming. However, some aspects of the Earth system, such as global mean temperatures1 and sea level rise due to thermal expansion2 or the melting of large ice sheets3, continue to respond long after the stabilization of radiative forcing. Here we use a coupled climate–vegetation model to show that in turn the terrestrial biosphere shows significant inertia in its response to climate change. We demonstrate that the global terrestrial biosphere can continue to change for decades after climate stabilization. We suggest that ecosystems can be committed to long-term change long before any response is observable: for example, we find that the risk of significant loss of forest cover in Amazonia rises rapidly for a global mean temperature rise above 2 ∘C. We conclude that such committed ecosystem changes must be considered in the definition of dangerous climate change, and subsequent policy development to avoid it.