Chichester Canal by JMW Turner. Image: Wikimedia Commons
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Image: Atmospheric Chemistry and Physics
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everywhere, with known early examples being the cave paintings at Lascaux in France and the “Swimmers in the Desert” at Gilf Kebir in south-eastern Sahara. The latter provides clear evidence that this part of the desert was once humid and green …Thus, there are numerous representations of climatic phenomena in pictures, which directly raises the question of whether these representations would be suitable as proxy data for climate research.There are some obvious questions that can be raised about all of this: What about color degradation over the course of a couple hundred years? What about different coatings and storage techniques? Why would we even want to do this? Zerefos writes that, because he's looking simply at the red-to-green ratio versus the absolute color of a painting, issues of degradation can be overcome, as can issues of painting coatings and storage. As for the "why," aerosol optical depth may be a basic measure, but it's a pretty useful one: Higher levels of aerosols are associated with cooler temperatures, because the particles reflect sunlight back into space. It's one of the reasons why aerosol seeding has been floated as a way of reducing global warming. AOD can be used in many climate models to estimate the general climate situation.Though his historical estimates line up with what we had already guessed, he decided to do the modern test with Tetsis to see how accurate he could be. He found that estimates based on Tetsis' paintings closely aligned with actually recorded AOD measurements.“During the two day experiment the substantial difference between the aerosol condition of the first and the second day provided a more adequate data set, supporting the assumption that a painter is able to reproduce such an aerosol change,” he wrote. “Quantitatively it has been proven that this assumption was correct.”Of course, estimating aerosol content of the atmosphere in the 1600s is never going to be an exact science, and AOD is a relatively basic measure of what was going on at the time. But scientists will take what they can get, and it turns out landscape paintings are more than just pretty pictures.