Atmospheric circulation trends in millenium-length climate simulations

Previous research found that key elements of the atmospheric general circulation have undergone important shifts over the past decades and that these shifts act as both indicators and agents of anthropogenic climate change. However, the short observational record makes it difficult to study the exact magnitude of these trends as well as their seasonal and regional structure. In addition, it is unclear what the exact causes for these trends are and how the trends will evolve with respect to future climate change.

Here, we answer these questions with results from a large suite of time-slice experiments using the atmospheric component of the GFDL climate model AM2.1. Each simulation is driven by a unique combination of anthropogenic forcings and sea surface temperatures, and is between 500 and 1000 years long, allowing for very high confidence in our results. In addition, each simulation is carried out with a stratosphere- and a non-stratosphere-resolving version of the model in order to gain insight into how sensitive the model results are to the representation of the stratosphere.

We demonstrate how increases in greenhouse gases, depletion and recovery of stratospheric ozone, and warming sea surface temperatures individually and in their various combinations impact the atmospheric circulation. Many different aspects of the circulation are examined, including the annular modes, the Hadley cell, the tropopause, and the subtropical jets. Moreover, the length of the simulations allows us to investigate how much natural low frequency variability is associated with the individual trends. Finally, we illustrate the consequences of these shifts in terms of changes in hydroclimate at the surface. 7-28-2009-->