Wind speeds around the world seem to be decreasing in a phenomenon known as ‘stilling’ and European scientists are hoping to find out why.
The average terrestrial wind speed has slowed down half a kilometre per hour every decade since the 1960s. Image – Pixabay/ Free-Photos
Few people have probably noticed, but the world’s winds are getting slower. It is something that cannot be picked up by watching the billowing of dust or listening to the rustle of leaves on nearby trees.
Instead, it is a phenomenon occurring on a different scale, as the average global wind speed close to the surface of the land decreases. And while it is not affecting the whole earth evenly, the average terrestrial wind speed has decreased by 0.5 kilometres per hour (0.3 miles per hour) every decade, according to data starting in the 1960s.
Known as ‘stilling’, it has only been discovered in the last decade. And while it may sound deceptively calm, it could be a vital, missing piece of the climate change puzzle and a serious threat to our societies.
Dr Cesar Azorin-Molina, a climatologist at Sweden’s University of Gothenburg and lead researcher of the EU-funded STILLING project, believes there is an urgent need to determine the causes of stilling in a changing climate.
While 0.5 kilometre per hour might barely seem enough to ruffle any feathers, he warns that prolonged stilling will have serious impacts.
‘There are serious implications of wind changes in areas like agriculture and hydrology, basically because of the influence of wind on evaporation,’ said Dr Azorin-Molina. ‘A declining trend in wind speed can impact long-term power generation, and weaker winds can also mean less dispersion of pollutants in big cities, exacerbating air quality problems and therefore impacting human health.’
Global wind hunt
Dr Azorin-Molina is attempting to unravel whether stilling is a recent phenomenon due to human-driven climate change or if it occurred in the past as part of larger climate cycles.
To do this, he and his supervisor, Prof. Deliang Chen, are ‘rescuing’ global wind speed observations dating back to the 1880s.
‘It’s about knowing the past wind climate to understand the present stilling,’ explained Dr Azorin-Molina. ’From there, reliable future wind speed projections are needed for climate change adaptation.’
The project’s worldwide hunt for historical weather records has unearthed Portuguese weather books from the Azores Islands, starting from 1907. It also has observations from the Blue Hill Observatory, in Milton, Massachusetts, USA, which date back to 1885.
All of this data is being digitised and then homogenised through comparison to reference data series so that it is of a high enough quality to use in investigating stilling.
‘Together, it will give us new insights into wind variability in regions never analysed before,’ said Dr Azorin-Molina. With this data, he hopes it will be possible to unravel some of the possible causes that could be responsible for stilling — something vital in order to help nations make decisions about how to adapt to the social, economic and environmental impacts of any progressive stilling.
Among the leading theories is that urbanisation and changing land use is increasing the roughness of the land surface, slowing down winds. Others suggest that climate change may be behind the drop due to changing patterns in the way air circulates around the planet. Or it could be due to ageing wind speed instruments producing inaccurate results.