They say a picture is worth a thousand words, but it turns out that old paintings could also hold some pretty useful scientific data.

Scientists from Greece and Germany reckon that paintings of sunsets – up to 500 years old – could be used as a fairly accurate record of air quality. They found that in the years immediately after major volcanic eruptions, painters tended to use more red hues rather than greens in their depictions of sunsets.

So why is this the case? It turns out that the colour of the sky at sunset can change depending on the amount of dust in the air. The dust acts as a filter, reflecting certain wavelengths of light by different amounts. The dust tends to reflect shorter wavelengths (that our eyes interpret as the colours blue and green) more than longer wavelengths (red).

As a result, if there is a lot of dust in the air (for instance in the few years after a major volcanic eruption), less blue- and green-coloured light will pass through the atmosphere and the sky will appear redder.

So the researchers hope that some of the masterpieces of the world’s great artists may have unwittingly recorded useful scientific information about the amount of dust in the air at the time. It probably also gave them an excuse to travel around the famous art galleries of Europe.

So, what’s the point?

Figuring out how certain historical events, such as volcanic eruptions, affect the earth’s atmosphere can help us to understand how climate can be altered. This can help us to predict how the climate could change in the future by both natural and man-made factors.

Obviously there were no sophisticated ways to measure air quality 500 years ago, so evidence has to be pieced together from a range of sources including written accounts, ice cores and looking at the intensity (which is inherently linked to the colour) of light from the sun and other stars.

Nowadays, we have the technology to accurately measure the intensity of sunlight that reaches earth and we can use this to figure out how much dust is in the air. However, the equipment to do this (rather epically called a ‘pyrheliometer‘) has only been around since the 1880s so before this time, another source of information needs to be used.

This is where the paintings come in: they could provide the extra evidence needed to figure out how volcanic activity changed the quality of the air in different parts of the world at different times.

What did they do?

The researchers analysed over 500 paintings containing sunsets, dating from the year 1500 right up to 2000. They compared the ratio of red to green colours used in the sky in each painting and compared this to ice core and pyrheliometric data, as well as known dates of large volcanic eruptions.

Did they prove anything?

Although it might seem like a total long-shot, the study did indeed find that the red-green ratio in the paintings shifted to be more red in the years immediately after a massive volcanic eruption. They found this happened ‘regardless of the school or style of the painter’.

In addition, when volcanic dust years were excluded, they found that the red/green ratios of the paintings also largely followed the amount of sulfur found in ice cores. This is particularly strong after 1850 (industrial revolution), where the amount of sulfur and red/green ratio both increase significantly.

So, what does it mean?

On the surface, their idea might seem a bit far-fetched, but the researchers may well be on to something: While the matches are not perfect (and let’s face it, who would expect it to be perfect?), there do seem to be genuine correlations between the red/green ratio of the paintings and atmospheric events.

What is really interesting about this study, is that the scientists have really thought outside the box in an effort to find evidence. It does seem to be genuinely inspired to think: “Nowadays we could use photographs to figure out the colour of the sky, so maybe old paintings would contain the same information.”

Of course you can’t assume that the paintings are as true to life as a photograph, but if you look at lots of them, over a long period of time, and spot the same pattern (more red after eruptions) again and again, the theory is more believable.

The researchers conclude quite poetically that ‘nature speaks to the hearts and souls of the artists… the [red/green] ratios perceived by the brain contain important environmental information.’ Since artists try to translate what they see in real life onto canvas, it makes sense that the extra redness in the sky would lead to extra redness into the paintings.

It is very easy to think that in a time before sophisticated scientific equipment, there is no record of certain things (like the amount of volcanic dust in the air). But the scientists here have shown that sometimes, if you look in the right place, the information you want might be right in front of you. It might even be beautiful.

Original article in Atmospheric Chemistry and Physics Mar 2014

All images are open-source/Creative Commons licence.

Credit: C Monet (First); J Berry (Second); W Lim (Third); F du Puigaudeau (Fourth)

Text © thisscienceiscrazy. If you want to use any of the writing or images featured in this article, please credit and link back to the original source as described HERE.

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