Simon F. B. Tett, Richard Betts, Thomas J. Crowley, Jonathan Gregory, Timothy C. Johns, Andy Jones, Timothy J. Osborn, Elisabeth Öström, David L. Roberts, Margaret J. Woodage

Climate Dynamics

Published date September 22, 2006

The impact of natural and anthropogenic forcings on climate and hydrology since 1550

  • Runs a climate simulation of an ocean/atmosphere general circulation model driven with natural forcings alone (constant “pre-industrial” land-cover and well-mixed greenhouse gases, changing orbital, solar and volcanic forcing) from 1492 to 2000
  • Also carries out another simulation driven with natural and anthropogenic forcings (changes in greenhouse gases, ozone, the direct and first indirect effect of anthropogenic sulphate aerosol and land-cover) from 1750 to 2000
  • These simulations suggest that since 1550, in the absence of anthropogenic forcings, climate would have warmed by about 0.1 K
  • Compares a simulation driven by anthropogenic and natural forcings with a natural-only simulation, which suggests that anthropogenic forcings have had a significant impact on, particularly tropical, climate since the early nineteenth century
  • Finds that both the hydrological cycle and cryosphere are also affected by anthropogenic forcings
  • Finds that changes in tree-cover appear to be responsible for some of the local and hydrological changes as well as an increase in northern hemisphere spring snow cover

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