Evaluating Changes to Natural Variability in the Ocean on a Warming Globe in CMIP5 Models

Natural variability in the global oceans has been shown to influence the Global Mean Surface Temperature (GMST). However, how oceanic variability and its contribution to the GMST change on a warmer globe is not fully understood. We analyze 19 models from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) to understand how the variance within the ocean will change under different warming scenarios. Utilizing pre-industrial, historical, and future warming simulations, we employ various metrics and techniques including EOF decomposition, running climatologies, along with linear and nonlinear trends to elucidate how natural variability changes over time. We also examine the changes to natural variability over different regions by running our analysis by basin, hemisphere, along the tropics, and different latitude belts. Results suggest that natural variability for much of the global oceans decreases as the amplified forcing by experiment increases. Mechanisms for the changes in variance among individual modes are also examined.