Global warming levels masked by aerosols: study

High levels of aerosols, spewed from coal- and gas-powered power plants, cooled our atmosphere, masking up to a third of global warming caused by greenhouse gases last century.

And when Europe cleaned up its sulfur emissions, it inadvertantly gave Arctic warming a boost.

A study led by geoscientist Trude Storelvmo at Yale University and published this week in the journal Nature Geoscience bypassed climate modelling and instead observed temperature, greenhouse gas levels and surface radiation from 1,300 surface sites from across the globe from 1964 and 2010.

For the first 30 years or so, less sunlight reflected from Earth back into space, a phenomenon known as “global dimming”.

Sulfate aerosols in the atmosphere pointed the finger at human involvement. When coal is burnt, for instance, sulfur dioxide (SO₂) molecules released into the atmosphere form tiny aerosol particles. These particles are particularly effective at bouncing sunlight back into space.

But around the turn of the century, this global dimming eased, gearing instead towards “global brightening”. Today, European sulfur emissions are less than a quarter of their peak in the 1970s, writes Thorsten Mauritsen, a climate scientist at the Max Planck Institute for Meteorology, in an accompanying News and Views article.

The researchers then analysed changing temperatures in relation to levels of solar radiation and greenhouse gas concentrations.

The findings suggest “about one-third of potential continental warming attributable to increased greenhouse gas concentrations has been masked by aerosol cooling during this time period”.

A second study in Nature Geoscience looked at the effects of European air pollution on Arctic warming.

Researchers at Stockholm University used regional models of aerosol levels to highlight a reduction in Europe’s air pollution since 1980, and SO₂ in particular. But the Arctic warmed faster during this period.

“Our study shows that the SO₂ emission reductions in Europe since the 1980s have contributed significantly to the enhanced Arctic warming,” the paper reads.

The paper suggests that, in light of ever-fewer aerosols, “the recent trend of amplified Arctic warming will be further strengthened”. The focus on reducing greenhouse gas emissions is more important than ever.