Dr. Craig Jackson (Department of Mathematics and Computer Science)

Feedback processes are extremely important in determining the shape of the global response to climate forcing. In particular, it has long been known that the climate exhibits a polar-amplified response to any globally uniform forcing such as a doubling of CO2. This polar-amplified response is due to the interaction of several feedback processes (e.g., ice albedo, lapse rate, and water vapor feedbacks). However, determining the relative strength of these feedbacks and how they interact is not a straightforward problem.

There are a variety of methods to assess the strength of individual feedback processes in numerical climate models. Generally these methods compute, in some form, the ratio of free- and fixed-feedback temperature anomalies when the model is subjected to forcing. However, these ratios (gains) are often sensitive to the overall shape of the applied forcing. For example, an ocean-atmosphere coupled model subjected to an equatorially amplified forcing will result in different gains and feedback factors (both global and local) than the same model subjected to a polar-amplified forcing.

Students interested in feedbacks in the climate system can work on projects related to developing and refining a more general matrix method of feedback analysis. This method produces matrices that generalize (both globally and locally) the classically defined numerical gains and feedback factors and are independent of the applied forcing. Moreover, in the case of a feedback process that is not purely a function of local temperature, these matrices will show the degree to which this “local feedback process” depends on non-local perturbations.