"This paradox between predictions and observations has been confusing scientists for more than 10 years," Jian Ma of Shanghai Ocean University, China, told environmentalresearchweb. "We felt that it was important to see if these different views could be reconciled."

Calmer winds would make it harder for air pollution to disperse, potentially leading to a greater number of hazy days. But the investigation carried out by Ma and his colleagues, who are based in China and the US, leans towards more favourable weather conditions.

Reporting their results in Environmental Research Letters (ERL), the team compared the output of 19 CMIP5 models with readings from the WASWind (Wave and Anemometer-based Sea Surface Wind) dataset. The WASWind approach corrects for wave height so that the ship-based measurements don’t overstate wind speed.

Looking at the big picture, Ma and colleagues argue that in the tropics, the sea surface temperature pattern acts against the large-scale circulation slow-down. And for higher latitudes, they report that the surface winds shift poleward along with the eddy-driven mid-latitude westerlies. Combined, these dynamic processes appear to prohibit major changes in tropical and global mean surface wind speed.

To screen out the hypothesis that the non-weakening of surface winds is linked to the debated global warming "hiatus" of the mid-1990s, the team’s analysis focused on the period between 1970 and 1995.

The scientists found that even in the tropics, where tropospheric circulation tended to slow down, the spatial-mean surface wind speed displayed a positive trend. And they believe this to be consistent with microwave measurements.

So while high levels of greenhouse gases represent bad news for the climate as a whole, in terms of surface wind the various mechanisms at work appear to cancel each other out to some degree. At least for the time being.

More details on the study can be found in Environmental Research Letters (ERL).

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