Global Stilling refers to the measured reduction in average terrestrial surface windspeeds over the last 40 years.

Measurements worldwide have shown a reduction of between 5% and 15%.

There is currently no agreed explanation of the effect.

One suggestion is that it's due to increased 'surface roughness' from urbanisation.

The stilling may be a result of climate change, or may be an independent effect which could be affecting climate change. (Note the reduction has implications for the future efficiency of wind-driven electricity turbines.)

A 2019 report in Nature Climate Change suggests, however, that the stilling process may have reversed around 2010, and could be due to decades-long climate oscillations (which are not yet quantified or understood.)

Here, we use wind data from in situ stations worldwide to show that the stilling reversed around 2010 and that global wind speeds over land have recovered. We illustrate that decadal-scale variations of near-surface wind are probably determined by internal decadal ocean–atmosphere oscillations, rather than by vegetation growth and/or urbanization as hypothesized previously.

Source : Nature Climate Change volume 9, pages 979–985 (2019)