Climate Variability, Climate Change and Earth System Sensitivity

This chapter addresses climate variability and climate sensitivity. Understanding climate variability is important for estimating how future climate will respond to changes in the greenhouse gas concentration in the atmosphere. The chapter approaches climate sensitivity as Earth system sensitivity. This makes it possible to investigate sensitivity at both current and geological timescales. Climate change is examined in terms of geological-scale variability, glacial variability and centennial-scale variability. The chapter starts by distinguishing between slow (geological, ice sheets) processes and fast (anthropogenic) processes, where the slow processes may provide boundary constraints to the faster processes. It first analyses Cenozoic temperature variability and then examines the periodical variations in carbon dioxide and temperature that occurred during the glacial–interglacial cycles in the Pleistocene. It concludes by discussing the fundamental changes in the atmosphere that have arisen as a result of both the burning of fossil fuel and the change in land use by humans.