Studying global warming through old masters' paintings

Researchers are studying the painted sunsets by artists like Turner, Rembrandt, and Rubens to get a sense of how volcanic eruptions may have impacted global warming. The National Observatory of Athens scientists look at the colors the old masters used in their depictions to suss out the amount of volcanic ash was in the atmosphere. The historical data will then help populate computer simulations of global warming. 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.