Radiative forcing and climate sensitivity: The ozone experience

• Published in: Quarterly Journal of the Royal Meteorological Society
• Main Author: Christiansen, Bo
• Other Authors: Commission of the European Communities, Nordic Council of Ministers
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1999
• Subjects: Sea ice
• Online Access: http://dx.doi.org/10.1002/qj.49712556011; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fqj.49712556011; https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.49712556011

Abstract The climatic impact of ozone perturbations is studied with a general‐circulation model by considering both the radiative forcing at the tropopause and the change in the near‐surface temperature. In particular, we focus on the vertical sensitivity by imposing the perturbations in different vertical layers. the simulations are done in perpetual‐January mode and with climatological sea ice. the main part of the analysis is focused on global‐mean values and in particular on the surface energy budget. Moderate sensitivities related to weak positive feedbacks are found when the perturbation is applied to the troposphere or the lower stratosphere, while larger sensitivities are found for perturbations in the higher stratosphere. This difference in the feedbacks is argued to be related to the vertical partitioning of the radiative forcing determined by the relative strengths of the long‐wave and short‐wave forcings. While the larger part of the short‐wave forcing, which dominates for ozone perturbations in the higher stratosphere, penetrates to the surface, the long‐wave forcing is predominantly deposited in the free troposphere. When the model is forced at the surface, latent‐heat flux effectively transports energy to the free troposphere restoring the lapse rate to its unperturbed value. Conversely, when the forcing is located in the free troposphere transport to the surface is limited. For the experiments under consideration the radiative forcing and the climate sensitivity are found to be robust and only slightly sensitive to the definition of the tropopause. As a measure of climate change the forcing adjusted for thermal changes in the stratosphere is superior to both the instantaneous forcing and to the forcing obtained after dynamical changes in the stratosphere.