Climate Number: One Foot per Second
Wind speed affects surface evaporation, air quality, soil erosion, wind power generation, etc. Trends in global wind speed due to related large-scale global processes have direct implications for weather and environmental quality as well as indirect implications for the global energy budget via wind speed ‘s influence on aerosol concentrations and the water cycle. Globally, there has been a “stilling” trend over the last 30 years, meaning that near surface wind speeds – wind speeds at 33 feet (10 meters) off the surface – are on average blowing slower than they were in the late 1970s. Averaged over the Northern Hemisphere mid-latitudes, this 30-year trend is a slowing of approximately one foot per second. Several mechanisms are likely driving this trend. Increases in surface “roughness,” vegetation cover and vegetation height due to changes in agricultural and forestry practices, are believed to be slowing down these winds. Other influential factors include sea surface temperature changes, changes in aerosol loading and changes in greenhouse gas concentrations. Sea surface temperature changes affect the difference between ocean and land surface temperatures: this temperature difference drives winds throughout the world and is particularly important in monsoon regions like India, China and the American Southwest. Aerosols, such as dust and soot, work to cool the surface by blocking or absorbing incoming sunlight, but also warm the layer of the atmosphere where their concentrations are highest. This ultimately works to slow down the general atmospheric circulation and reduce surface wind speeds.
Seasons: Winter, Spring, Summer and Fall
Source: Bichet, A et al. “Causes for decadal variations of wind speed over land: Sensitivity studies with a global climate model.” Geophysical Research Letters 39 (2012): L11701.