Good news: cutting down use of aerosols saved the ozone layer. Bad news: it might have made global warming worse.
That's the conclusion reached by scientists in Europe and the US, who've found evidence aerosol gases and other sulphate emissions were keeping parts of the planet cooler by dimming solar radiation.
The effect has been most pronounced in the Arctic, contributing to a rise of 0.5degC, Trude Storelvmo and colleagues at Yale and Stockholm universities write in journal Nature Geoscience.
This is because aerosol usage and sulphate emissions in Europe and North America have dropped significantly in the last three decades, more than offsetting increased emissions in Asia.
"Air quality regulations in the Northern Hemisphere, the ocean and atmospheric circulation and Arctic climate are inherently linked," the authors write.
It is estimated aerosols were masking a third of the expected rise in land temperatures, and global temperatures will rise by 2degC once carbon dioxide levels reach double pre-industrial levels.
An accompanying editorial argues, however, the effect of aerosol and sulphate emissions on keeping global warming in check worldwide was minor.
"Ultimately, it is not the uncertain temporary aerosol cooling, but the warming induced by long-lived greenhouse gases such as carbon dioxide that has warmed the Arctic in the past -- and will continue to do so," writes Thorsten Mauritsen of the Max Planck Institute for Meteorology.
"As we look to the future it is highly likely that European sulphur emissions will continue to plummet in coming decades. But we have already seen most of the reductions, and so the remaining Arctic cooling from European sulphur emissions is hardly more than a couple of tenths of a degree."
Last year, most of the world's countries agreed in Paris to work towards keeping global temperatures to under 2degC above pre-industrial levels.