How 19th Century Art is Painting a Picture of Earth's Polluted Past: Turner's Sunsets Reveal Volcanic Ash and Gas in the Sky

He was one of Britain’s greatest ever painters, his works lauded for their atmosphere and visual mastery. Scientists, however, have found another  reason to marvel at the pictures of J.M.W. Turner – they believe they will help them to assess how polluted the world once was. They say landscapes by artists such as Turner accurately recorded the chemicals in the air.

The key, according to the atmospheric physicists, is in the colour of the sunsets they depicted. Scientists analysed hundreds of paintings completed between 1500 and 2000, a period covering more than 50 major volcanic eruptions around the globe.

The results, published in the journal Atmospheric Chemistry and Physics, reveal that when the Tambora volcano in Indonesia erupted in 1815, painters could see the colours of the sky changing.
The volcanic ash and gas that was spewed into the atmosphere travelled the world and as these aerosol particles scattered sunlight, they produced bright red and orange sunsets in Europe for up to three years after the eruption.

Dr Zerefos and his team analysed hundreds of high-quality digital photographs of sunset paintings created between 1500 and 2000, during which time there were 50 large volcanic eruptions around the globe. 
They were looking to find out whether the relative amounts of red and green along the horizon of each painting could provide information on the amount of aerosols in the atmosphere.

Dr Zerefos said: ‘We found that red-to-green ratios measured in the sunsets of paintings by great masters correlate well with the amount of volcanic aerosols in the atmosphere, regardless of the painters and of the school of painting.’
Skies more polluted by volcanic ash scatter sunlight more, so they appear redder and similar effects are seen with mineral or man-made aerosols. 

Air with a higher amount of aerosols has a higher 'aerosol optical depth' - a parameter the team calculated using the red-to-green ratios in the paintings. 
They then compared these values with those given by independent proxies such as ice core and ‘volcanic- explosivity’ data to find a good correlation.

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