What do we know about past changes in the latitudinal extent of the tropics? --- An incomplete understanding

Abstract:

Latitudinal shifts in tropical poleward extent are significant from a climatic point of view, in particular when considering location of the subtropical dry zones. Another concern is expanding the upwelling region into the stratosphere; this could potentially increase the transport of ozone depleting substances and sulfate aerosol precursors into the stratosphere as the upwelling region expands over high emission source areas. Changes in tropical width were also hypothesized to play a role in stratospheric water vapor trends.

Evidence for the changing the latitudinal extent of the tropics comes from multiple sources, including changes in subtropical tropopause height, column, temperature distributions and circulation statistics. Causes have been suggested to be due to increases in greenhouse gases as well as changes in the stratospheric ozone distribution. However, it is important to note that unraveling the fundamental causes of observed changes is a work in progress.

In this presentation I will review the existing literature on tropical width trends, discuss various metrics used, possible relations to global indices, and climate implications.