Reconstructing atmospheric history

Old paintings can provide information about the composition of the atmosphere of bygone ages. When a volcano erupted in Indonesia in 1815, painters in Europe painted bright red and orange sunsets. Ash and gases released during major volcanic erruptions can make sunsets appear more red, says Christos Zerefos, professor of atmospheric physics at the Academy of Athens in Greece.ÔÇêZerfos and his team published a model toÔÇêgauge climate conditions from paintings in the journal Atmospheric Chemistry and Physics on March 25. He discusses the model with Vibha Varshney. Edited excerpts

 
By Vibha Varshney
Last Updated: Saturday 04 July 2015

interviewPlease describe your model
We analysed hundreds of painting and found that the ratio of red and green colours used to paint cloudless sunsets provides alternative ways of exploiting the environmental information in the past atmosphere in places where, and in centuries when, instrumental measurements were not available. Our studies have shown that though “nature speaks to the soul of artists”, the colours perceived by the brain of the artist, have important environmental information about the amount of aerosols in the air. If one repaints the paintings by putting numbers to red and green ratios, the result is the cloud overhead as would be expected from atmospheric physical theory.

Is the model reliable?
We asked a famous colourist to paint sunsets during and after the passage of a Saharan dust cloud over the island of Hydra, Greece, in 2010. The painter was not aware of the dust event. We compared measurements of the aerosol optical depth, a parameter to calculate the red-to-green ratios, made by modern instruments with those estimated from the red-to-green ratios of the paintings, we found that they matched.

How did you get the idea that this method would work?
The idea came from the measurements we do with spectrophotometers where we take ratios of colours to estimate the amounts of atmospheric gases.

How would your findings help?
Our findings provide a new look at the capability in the brain to decipher ratios of colours. We provide independent evidence confirming what has been reported with different data and methods.

Air with a higher amount of aerosols has a higher aerosol optical depth (AOD). We found that AOD at 550 nm calculated from the paintings grew from 0.15 in the middle of the 19th century to about 0.20 by the end of the 20th century. Aerosol optical depth can be directly used in climate models, so having estimates for this parameter helps researchers understand how aerosols have affected the earth's climate in the past. This, in turn, can help improve predictions of future climate change.

There are, I believe, important implications for further interdisciplinary work which should include experts in brain research. We do look to proceed forward in this direction.

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