The End of the Wait for Climate Sensitivity?

The Earth system responds on a range of timescales to a change in radiative forcing, and full equilibration takes centuries to millennia in many models. In their recent paper, Saint‐Martin et. al (2019, https://doi.org/10.1029/2019GL083031) propose a technique for reaching a faster equilibrium temperature response to alternative CO2 concentration levels by briefly overshooting the desired concentration level to warm the deep ocean faster than a conventional step change experiment. Understanding how these timescales interact is essential for better representing the relationship between transient climate change and the warming which should be expected as greenhouse gas concentrations stabilize. But the technique also raises new possibilities about how Earth System Models could be developed and whether we could gain the capacity to spin‐up alternative model configurations such as perturbed parameter simulations or alternative control states to explore historical forcing uncertainty. Key Points: Understanding climate dynamics with feedbacks on multiple timescales remains a challengeThe approach of Saint‐Martin et al provides a novel opportunity for reaching faster climate equilibriumThis approach could be extended to allow alternative configurations of Earth System Models without lengthy ocean spin‐ups [ABSTRACT FROM AUTHOR]