Abstract

Analysis of Climate Feedbacks

Student: Carina DiChello
Faculty Mentor: Craig Jackson (OWU Department of Mathematics and Computer Science)

There are a number of systems that strengthen or weaken the changes in global Earth surface temperatures that are expected to result from an increase in atmospheric carbon dioxide. These systems are called feedbacks. One important feedback system depends on the reflectivity of snow and ice. In my research I used a spatially resolved numerical climate model to analyze the local and non-local contribution of this individual feedback process to surface warming. An understanding of the mechanisms underlying climate feedback systems is important to scientists when trying to understand the spatial distribution of surface temperature in future global warming scenarios.

In the Earth climate system there are a number of important feedback systems. A feedback is a geophysical sub-system of the climate that acts to amplify or dampen the temperature change in response to forcing (for example, due to increased atmospheric carbon dioxide). One important feedback process is the ice albedo feedback. Ice albedo refers to the degree to which the sun’s energy is reflected back into space by relatively reflective snow and ice. When the earth warms and the ice and snow melt, then there is less ice surface to reflect solar energy which leads to further warming. Ice albedo feedback is a positive feedback, meaning it amplifies the change in surface temperature that we would see if the feedback was not active.

In this research, a matrix-based approach to feedback analysis is developed and used to analyze the local and non-local contribution of ice albedo feedback to surface warming in fully generic forcing scenarios in the context of a spatially resolved numerical climate model developed by Dommenget and Floer. In particular, gain matrices are derived that encode the extent to which non-local changes in surface temperature are integrated by the feedback process to shape the global temperature anomaly when the model is run with the feedback activated. We observe that ice albedo feedback causes extratropical temperature anomalies to contribute positively to temperature changes in the tropics as expected. Interestingly, however, we see that tropical temperature anomalies contribute negatively to the temperature response in the extratropics. We show how such behavior can be explained in the context of a conceptual two box energy balance model where a local tropical temperature increase leads to an increased latitudinal temperature gradient and therefore cooler polar temperatures, resulting in more planetary snow/ice. We hypothesize that a similar explanation holds in the more complex spatially resolved model.