Connections between stratospheric ozone and climate: Radiative forcing, climate variability, and change

Quantifying the combined effects of ozone depletion and changes in other greenhouse gases and radiatively and chemically active atmospheric constituents is of great importance to human welfare. Achieving this goal requires evaluating the impact of stratospheric ozone depletion and its recovery on the tropospheric climate as well as elucidating the effects of climate change on the evolution of ozone itself. This, in turn, requires the understanding and quantification of the long-term sensitivity of the climate system to significant perturbations in the radiation budget of the atmosphere associated with human activities. Detecting and quantifying such effects also requires a quantitative understanding of the role of natural events, such as volcanoes and solar variability, on the composition and evolution of the atmosphere and ultimately of the effects of such events on the climate change signal throughout the active atmosphere and at the surface. With the advent of climate modelling as a key tool for studying and predicting the evolution of the climate system, the linked concepts of radiative forcing and climate sensitivity have come into wide use as a means to understand and quantify key aspects of modelling results. These concepts are reviewed and their relevance to understanding and quantifying the radiative impact of ozone and ozone depleting substances on the radiative forcing of the climate system are discussed. Recent observational, theoretical, and modelling studies have revealed many new features of stratosphere-troposphere coupling that are relevant to understanding the role of stratospheric processes in climate variability and change. Aspects of these studies are reviewed briefly.