Perspectives on Climate Sensitivity and Ocean Heat Uptake

The notion of climate sensitivity has become synonymous with Equilibrium Climate Sensitivity (ECS). But, 21st century warming is affected at zeroth order by ocean heat uptake, which isn't accounted for by ECS but is accounted for by the Transient Climate Response (TCR). In this talk, we highlight some potentially underappreciated aspects of TCR and ocean heat uptake, using the two-box ocean model as a common theoretical framework. We emphasize that i) TCR can be scaled by the forcing to estimate transient temperature change across a variety of scenarios, ii) this scaling can be used to estimate the time to cross a given temperature target in a given forcing scenario, using only a model's TCR, and iii) the two-box model predicts a linear relationship between ocean heat content and surface temperature which is inconsistent with most models. This talk is based on an forthcoming article in Annual Reviews of Earth and Planetary Sciences.