Sack Lunch Seminar (SLS)

While constraining climate sensitivity has long been a focus of our field, this global and equilibrium metric provides only limited understanding of aspects of future climate that are of critical interest to society--namely transient and regional changes over the coming centuries. Pronounced spatial and temporal variability in climate change has been observed, and models diverge strongly in projections of the structure and rate of future warming. Moreover, differences in equilibrium climate sensitivity explain only about half of the intermodel spread in transient global warming; the other half can be attributed to differences in the degree to which climate sensitivity varies over time as the Earth warms.

Here I discuss mechanisms governing the time variation of climate sensitivity and the geographic structure of transient climate change. I show that expressing global climate sensitivity in terms of the contributions from regional climate feedbacks provides clear physical insight: Climate sensitivity depends centrally on the respective geographic patterns of radiative feedbacks and surface warming, and thus its time variation arises naturally when the pattern of surface warming evolves, activating feedbacks of different strengths in different locations. As a concrete example, I highlight the Southern Ocean, where radiative feedbacks are strong and positive near the sea-ice edge yet anthropogenic surface warming is delayed due to local ocean processes: slow warming over the coming centuries will activate destabilizing local feedbacks, increasing the net energy flux into the climate system and remotely warming mid to low latitudes through anomalous atmospheric energy transport. I argue that since the pattern of global warming is largely regulated by ocean dynamics, the ocean inherently controls the global energy budget, and climate sensitivity, through its regional-scale coupling to atmospheric radiative feedbacks.