Modeling the influence of water vapor

Liz Kalaugher in Environmental Research Web: As climate change proceeds and temperatures rise, the amount of water vapour that the atmosphere can hold will increase. This will have implications for patterns of precipitation and evaporation, energy transport by latent heat fluxes, radiative transfer and freshwater exchange with the ocean. With that in mind, a team from MIT, US, has investigated "in a more careful way than previously" the factors that determine the rates of change of total water vapour in simulations of global warming.

"It has long been known that climate models predict that the amount of water vapour goes up at roughly the same rate as the water vapour holding capacity, corresponding to constant relative humidity," Paul O'Gorman of MIT told environmentalresearchweb. "But the relative humidity is not exactly constant in simulations, and we wanted to ascertain exactly how much these small changes in relative humidity affected the rates of changes in the total amount of water vapour, and how much the rates of change varied regionally. We also wanted to compare the changes in the amount of water vapour near the surface and in the whole atmosphere."

By using climate models from the World Climate Research Programme's Coupled Model Intercomparison Project (CMIP), O'Gorman and colleague Caroline Muller calculated the rates of change in the amount of atmospheric water vapour between the last 20 years of the 20th century and the last 20 years of the 21st century under the A1B emissions scenario.

"We showed that the systematic changes in relative humidity had almost no effect on the rate of change of global water vapour in climate-model simulations of global warming, even though they mattered locally," said O'Gorman….

Sunlight through fog in Albequerque, New Mexico, shot by Tate Strickland, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 3.0 License.