Role of Stratospheric Processes in Climate Change: Advances and Challenges

In this review, instead of summarizing all the advances and progress achieved in stratospheric research, the main advances and new developments in stratosphere-troposphere coupling and stratospheric chemistry-climate interactions are summarized, and some outstanding issues and grand challenges are discussed. A consensus has been reached that the stratospheric state is an important source of improving the predictability of the troposphere on sub-seasonal to seasonal (S2S) time scales and beyond. However, applying stratospheric signals in operational S2S forecast models remains a challenge because of model deficiencies and the complexities of the underlying mechanisms of stratosphere-troposphere coupling. Stratospheric chemistry, which controls the magnitude and distribution of many important climate-forcing agents, plays a critical role in global climate change. Convincing evidence has been found that stratospheric ozone depletion and recovery have caused significant tropospheric climate changes, and more recent studies have revealed that stratospheric ozone variations can even exert an impact on SSTs and sea ice. The climatic impacts of stratospheric aerosols and water vapor are also important. Although their quantitative contributions to radiative forcing have been reasonably well quantified, there still exist large uncertainties in their long-term impacts on climate. The advances and new levels of understanding presented in this review suggest that whole-atmosphere interactions need to be considered in future for a better and more thorough understanding of stratosphere-troposphere coupling and its role in climate change.