From The Guardian:
The results will feed into the scientific study of a phenomenon called global dimming, which is caused by air pollution blocking sunlight. Some experts believe this has acted as a brake on global warming, and that climate change could accelerate as air pollution from industry is reduced.
Professor (Christos) Zerefos and his team looked at natural global dimming caused by volcanoes, the results of which can be severe. The eruption of Mount Tambora in Indonesia in 1815 threw out so much material that it triggered the notorious "year without a summer", which caused widespread failure of harvests across Europe, resulting in famine and economic collapse.
The team found 181 artists who had painted sunsets between 1500 and 1900. The 554 pictures included works by Rubens, Rembrandt, Gainsborough and Hogarth. They used a computer to work out the relative amounts of red and green in each picture, along the horizon. Sunlight scattered by airborne particles appears more red than green, so the reddest sunsets indicate the dirtiest skies. The researchers found most pictures with the highest red/green ratios were painted in the three years following a documented eruption.
Prof Zerefos's team is now talking to the Tate in London about repeating the study with 40 paintings from the 20th century, to see whether artists have captured the effects of pollution on sunsets since the industrial revolution.
Big bangs
1783 Laki, Iceland Volcanic eruption spread sulphurous haze across western Europe, killing thousands.
1816 Tambora, Indonesia Eruption killed 10,000 people directly and 66,000 due to starvation and disease during "year without a summer" that followed, when temperatures plunged and harvests failed.
1883 Krakatoa, Indonesia Loudest recorded bang in history. At least 36,417 people died. Average global temperatures dropped by 1.2C.
1991 Pinatubo, Philippines Killed 300 people. About 17m tonnes of sulphur dioxide went into atmosphere, reducing sunlight by 5% and global temperatures by 0.4C.