CityReads│Master Paintings Tell Story about Air Pollution

CityReadsVol.80

Master Paintings Tell Story

about Air Pollution

Scientists gathered 554 sunset paintings by 181 artists between 1500 and 2000 and calculated the red/green ratios as proxy information for the aerosol optical depth after major volcanic eruptions and industrial pollution.

C. S. Zerefos, P. Tetsis, A. Kazantzidis, V. Amiridis, S. C. Zerefos, J. Luterbacher, K. Eleftheratos, E. Gerasopoulos, S. Kazadzis, A. Papayannis. Further evidence of important environmental information content in red-to-green ratios as depicted in paintings by great masters. Atmospheric Chemistry and Physics, 2014; 14 (6): 2987 DOI: 10.5194/acp-14-2987-2014

Source: http://www.atmos-chem-phys.net/14/2987/2014/acp-14-2987-2014.html

Picture source: Caspar David Friedrich, Woman in front of the Setting Sun, 1818. Credit: Caspar David Friedrich/Wikimedia Commons

Physicist Richard Feynman once had a conversation with his artist friend about art and science. His artist friend held up a flower and said, “I, as an artist, can see how beautiful a flower is. But you, as a scientist, take it all apart and it becomes dull.”

Feynman didn’t agree. He replied, “First of all, the beauty that you see is available to other people—and to me, too. Although I might not be quite as refined aesthetically as you are, I can appreciate the beauty of a flower. But at the same time, I see much more in the flower than you see. I can imagine the cells inside, which also have a beauty. There’s beauty not just at the dimension of one centimeter; there’s also beauty at a smaller dimension. (Science) only adds to the excitement and mystery and awe of a flower. It only adds. I don’t understand how it subtracts.”

A team of Greek and German researchers has shown that the colors of sunsets painted by famous artists can be used to estimate pollution levels in Earth's past atmosphere. In particular, the paintings reveal that ash and gas released during major volcanic eruptions scatter the different colors of sunlight, making sunsets appear more red. Deep red sunsets offer more than just a stunning backdrop for Old Masters' paintings: They can tell how dirty the air was when the painter picked up the brush. This is a case in point of what Feynman says about science and beauty, “science only adds beauty, not subtracts it.”

Christos Zerefos, who led the research, said: "We're taking advantage of the attitudes of famous painters to portray real scenes they were looking at. This is the first attempt to analyze this old art in a scientific way, and tells the story of how our climate has varied naturally in the past."

 How scientists analyze sunset paintings to learn air pollution?

Scientists analyze the sky color in the sunset paintings to estimate the degree of air pollution or the amount of airborne particles.

Tiny solid and liquid particles suspended in the atmosphere are called aerosols. Aerosols can come from natural sources such as volcanic eruptions, windblown dust forest fires or dust storms, or from manmade sources such as pollution from factories or soot from car and truck engines. Aerosols scatter sunlight so that sunsets appear more reddish.

The effects of aerosols on Earth's climate are complicated. Depending upon their size, type, and location, aerosols can either cool the surface, or warm it. They can have a major impact on climate when they scatter light, cooling the planet in the case of the eruption of Mount Pinatubo in the Philippines in 1991. Or they can absorb heat and, particularly with soot from diesel and coal smoke, hasten snow- and ice-melt.

They can help clouds to form, or they can inhibit cloud formation. And if inhaled, some aerosols can be harmful to people's health.

"Aerosol Optical Depth (AOD)" is the degree to which aerosols prevent the transmission of light by absorption or scattering of light.

But how can the scientists measure the aerosol optical depth in history, especially before the instrumental measurements?

When the Tambora volcano in Indonesia erupted in 1815, painters in Europe could see the colors of the sky changing. The volcanic ash and gas spewed into the atmosphere travelled the world and, as these aerosol particles scattered sunlight, they produced bright red and orange sunsets in Europe for up to three years after the eruption. J. M. W. Turner was one of the artists who painted the stunning sunsets during that time. 

The Lake, Petworth: Sunset, Fighting Bucks, by J. M. W. Turner

By correlating colors in paintings with aerosol optical depth, scientists found a way to retrieve information on the composition of the past atmosphere. They used the red/green ratios of sunset paintings by famous artists as proxy information for the aerosol optical depth after major volcanic eruptions and industrial pollution.

Scientists gathered 554 sunset paintings by 181 artists between 1500 and 2000, which 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.

AODs calculated from paintings were grouped into 50-year intervals from 1500 to 2000. The period included more than 50 large volcanic eruptions around the globe. The year of each eruption and the 3 following years were defined as “volcanic”. The remaining “non-volcanic” years were used to provide additional evidence of a multidecadal increase in the atmospheric optical depths during the industrial “revolution”.

The researchers found most pictures with the highest red/green ratios were painted in the three years following a documented eruption. The redder sunsets seen in paintings can be tentatively attributed to the volcanic events, and not to abnormalities in the color degradation due to age, or other random factors affecting each painter's color perception.

German artist Caspar David Friedrich's 1818 painting "Woman in Front of the Setting Sun" places the silhouette of a woman with outstretched hands under a deep ochre sky – a likely scene, the researchers say, given the 1815 eruption of Indonesia's Tambora volcano. That eruption scattered particles high into the atmosphere that produced bright red and orange sunsets throughout Europe for three years.

Karl Friedrich Schinkel, The Banks of the Spree near Stralau, 1817

Reddish hues in sunsets spiked during periods of volcanic activity. Edgar Degas, Race Horses, 1885.

They also found that depictions of sunsets have gotten redder from the Industrial Revolution onwards, even during periods of no volcanic activity. The increase of AOD at 550 nm calculated from the paintings grows from 0.15 in the middle 19th century to about 0.20 by the end of the 20th century. Artists are inadvertently capturing increases in pollution during the past 150 years.

You can see this in the above paintings by P. Tetsis and photos by C. Zerefos, showing the island of Hydra in 2010. The column on the left shows more aerosol and dust in the atmosphere — the sky looks slightly redder and hazier — than the right column.

Conclusion

Nature speaks to the hearts and souls of the artists. When coloring sunsets, the R /G ratios perceived by the brain contain important environmental information.

Regardless of the school, red-to-green ratios from great masters can provide independent proxy AODs that correlate with widely accepted proxies and with independent measurements.

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.

Using art to advance science is an emerging interdisciplinary field. The first meteorological measurements were not made until the 1850s, so paintings could be an important source of information on aerosols in the atmosphere at times before instrumental measurements. Art can be helpful to science research; and science can add beauty to art.

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