Historical paintings help us understand climate change
On April 10, 1815, Mount Tambora began to spew liquid rocks from deep beneath the earth’s crust, though earthquakes and ash preceded the eruption for several days. One of the most powerful eruptions in recorded history, the volcano’s effect on the planet’s climate was so drastic that global temperatures dropped for nearly a decade. It led to what some have called the 1816 “Year Without A Summer,” which was accompanied by food shortages, severe monsoons, and reductions in ocean temperature. In 1816, there was 80% more global rainfall than expected, particularly for Switzerland, France, Germany, and Poland. 1818 saw the opposite: unusually low rainfall, which caused droughts in most of Europe and Asia. While 10,000 people died as a direct result of the eruption, another 60,000 died due to indirect causes, such as starvation or disease.
Art and science meet in unexpected ways. Another result of the Tambora eruption, and indeed any large-scale eruption, was a reddening of the skies at twilight. That’s because the ash and other particulates that invade the skies scatter sunlight more than the earth’s atmosphere does on its own, so it appears redder. It’s one of the reasons why the smoggy Los Angeles sky is host to some spectacular sunsets. As a result, artists like England’s J. M. W. Turner who included sunsets in their landscapes, were unknowingly creating a sort of artistic record of atmospheric conditions during the time in which they were painting.
A group of Greek and German researchers, led by Christos S. Zerefos of the Academy of Athens, realized that they could use the colors included in those painted skies to better understand historical climate patterns. By comparing the amount of red and green in the painted sunsets, Zerefos was able to calculate the amount of volcanic aerosols in the sky in the place where the painting was created. Their findings have just been published in the journal Atmospheric Chemistry and Physics.
To demonstrate that the depictions of sunsets in paintings actually reflected an environmental reality, Zerefos created a measurement called “aerosol optical depth,” which was derived from the ratio of red and green pigments along the horizon in the paintings he examined. By including a wide variety of paintings, the variation due to color degradation due to aging, the different preservation techniques, the moods of the painters, and the different schools of art to which the painters belonged, could be accounted for, meaning any differences in color could be more reasonably attributed to actual differences in the sky’s coloration.
Zerefos compared the aerosol optical depth for paintings created between 1500 and 2000, a period that included more than fifty large eruptions, with other climate data. He used 100 paintings, all from the Tate Museum in London. As he expected, his model was consistent with information from Greenland’s ice cores.
To lend even further support to the notion that environmental information is preserved in art, Zerefos’s team asked a modern-day painter to paint sunsets during and after a Saharan dust cloud passed over the Greek island of Hydra in June 2010. Saharan dust particles create the same sunlight-scattering effect as volcanic ash. Importantly, the artist was unaware of the researchers’ motives. Zerefos then compared his paintings with digital photographs of the same scenes, and found that they matched. The ratio of red and green pigments in paintings can actually represent real atmospheric conditions.
Man-made pollution, too, scatters sunlight in similar ways as Saharan dust and volcanic ejecta. That makes aerosol optical depth an important ingredient in the recipe for understanding the ways that human behavior is altering Earth’s climate. The researchers say that by better understanding the skies of the past, we can better predict the skies of the future.– Jason G. Goldman | 2 April 2014
Source: Zerefos C.S., Tetsis P., Kazantzidis A., Amiridis V., Zerefos S.C., Luterbacher J., Eleftheratos K., Gerasopoulos E., Kazadzis S. & Papayannis A. & (2013). Further evidence of important environmental information content in red-to-green ratios as depicted in paintings by great masters, Atmospheric Chemistry and Physics Discussions, 13 (12) 33145-33176. DOI: 10.5194/acpd-13-33145-2013
Images: Top: The Lake, Petworth: Sunset, Fighting Bucks (c. 1829) by J. M. W. Turner, was one of the ones included in the analysis. Public domain. Bottom: P. Tetsis (paintings) and C. Zerefos (photos).