Apr 9, 2010

How closely do changes in surface and column water vapor follow Clausius–Clapeyron scaling in climate change simulations?

P A O’Gorman, C J Muller
Environmental Research Letters
  • Analyzes the factors governing the rate of change in the amount of atmospheric water vapor in simulations of climate change
  • Estimates the global-mean amount of water vapor to increase at a differential rate of 7.3K − 1 with respect to global-mean surface air temperature in the multi-model mean
  • Finds larger rates of change result if the fractional change is evaluated over a finite change in temperature (e.g., 8.2K − 1 for a 3 K warming), and rates of change of zonal-mean column water vapor range from 6 to 12K − 1 depending on latitude
  • Finds there are deviations from Clausius–Clapeyron scaling of zonal-mean column water vapor in the tropics and mid-latitudes, but they largely cancel in the global mean
  • Finds surface specific humidity increases at a rate of 5.7K − 1, considerably lower than the rate for global-mean water vapor
  • Finds surface specific humidity closely follows Clausius–Clapeyron scaling over ocean, but there are widespread decreases in surface relative humidity over land (by more than 1K − 1 in many regions), and it is argued that decreases of this magnitude could result from the land/ocean contrast in surface warming