A Stochastic Analysis of the Impact of Small-scale Fluctuations on Climate Sensitivity

Climate sensitivity is generally studied using climate models which have finite spatial and temporal resolutions. Different representations of subgrid-scale components can induce different types of small-scale fluctuations. These small-scale fluctuations can alter climate sensitivity via at least two mechanisms. First, the small-scale fluctuations could change the fluctuating behavior of the global mean temperature as measured by its statistical damping. The statistical damping acts as a restoring forcing that determines, according to the fluctuation-dissipation theory, the amplitude of climate response to a change in CO2 concentration. Second, the small-scale fluctuations could affect processes that occur only in response to the CO2 increase, thereby altering the effective forcing for global mean temperature. In this study, climate change experiments obtained from a comprehensive climate model with different representations of small-scale fluctuations are analyzed. By applying a stochastic model to the experimental results, the different roles of small-scale fluctuations on climate sensitivity are investigated.