Causes for decadal variations of wind speed over land: Sensitivity studies with a global climate model

Over the past 30 years, observations indicate a decline of about −0.3 m/s in the northern mid‐latitudes land surface wind speed. The picture is less conclusive for the Southern Hemisphere and over the oceans. Such a stilling can affect surface evaporation and climate feedback processes, and may impact technical applications such as wind power. Using an atmospheric global climate model, we perform sensitivity experiments for the period 1870–2005 to assess the role of changing roughness length, aerosol emissions, sea surface temperature, and greenhouse gas concentrations in surface wind speed changes. The wind speed trends simulated by the model generally underestimate the observed trends (land and ocean). Over land, the model can reproduce the observed stilling by increasing the roughness length by a factor of 1.2 to 4.9, depending on region. The other forcings examined can also decrease the 10 m wind speeds (up to 15% of observed values in Europe), particularly those related to increasing aerosol emissions (up to −0.2 m/s in India). Compared to observations, the simulated impact of climate forcings on global wind speeds over land and ocean is however small and not always significant. Key Points Roughness length should increase by a factor of 1.2‐4.9 to reproduce observation Aside from roughness length, atmospheric forcings decrease wind speed after 1950 Increasing aerosol emissions decrease the land wind speed by up to 0.3 m/s