Jun 17, 2009

Changes in the Atmospheric Circulation as Indicator of Climate Change

Thomas Reichler
  • States the most intriguing challenges regarding the atmospheric circulation and climate change are to understand what the nature of this change is, what the consequences for surface climate are, and what the underlying causes and mechanisms are
  • Focuses on: (1) tropical circulation change related to a poleward expansion of the Hadley cell (HC), and (2) extratropical circulation change, as manifested by a poleward shift of the zone of high westerly winds in the midlatitudes, also known as an enhanced positive phase of the annular modes (AMs)
  • States, as with most aspects of climate change, the circulation changes that occurred over the past are still relatively subtle, making it difficult to distinguish them from naturally occurring variations
  • States long-term records of the atmosphere exist at few locations only, and most regions of the Earth are not observed
  • Relies on observation-based evidence but also include findings from general circulation models (GCMs) due to the difficulty in observing the atmospheric circulation and its long-term trends
  • States alterations of the radiative balance of the Earth due to climate change modify regional temperature and humidity structures, and the winds respond to the resulting gradients and change the intensity and structure of the circulation
  • Finds there exists considerable scientific evidence that key-elements of the atmospheric circulation have been moving poleward during the last few decades
  • Finds that current theories as well as model experiments indicate that human activity in association with greenhouse gas increases and stratospheric ozone depletion is the most likely cause for the trends