What spectacular sunsets tell us

We had some spectacular sunsets last week. In this photo, the CN Tower in Toronto looms over the Rogers Centre under an orange-red sky.

At about the same time, coverage of the Chicagoland Nascar Sprint Cup race in Joliet, Illinois, paused for some incredible high definition beauty shots of the red sky over the race track.

Talking it over with Duilio Zane (my father and the photographer who took the stills shown here), the question arose whether the sunsets are becoming redder because of a higher concentration of atmospheric pollution.

Scientific American writes that a higher percentage of aerosols, particles suspended in the atmosphere, can result in the scattering of light waves resulting in a predominance of oranges and reds. These particles can arise from the burning of fossil fuels and the release of sulphur dioxide into the air.

So the redness in the sky indeed may be caused by internal combustion engines and their exhaust. However, when pollution is very heavy, the sun appears misty and out-of-focus, not clearly defined as it has been on some recent nights.

The magazine points out that aerosols in the sky can also come from natural sources like forest fires and volcanic eruptions.

Well, neither of those were present in Toronto and Chicago last weekend.

But this brings us to another interesting connection. A team at the Observatory of Athens is studying the paintings of old masters to see if they can learn something from the colours of their sunsets. Specifically they want to learn how natural climate change in the past can be used to build better computer models for the effects of global warming.

In the last century, a huge amount of natural pollution was thrown into the sky by volcanic eruptions like the one that shook Indonesia in 1883 when Mount Krakatoa blew its top. These eruptions changed the colour of the sky for years afterward, and paintings from those periods show a lot of orange and red in the sky. See Edvard Munch's The Scream (1893).

By analyzing the colours and feeding the data into computers, scientists hope to understand a modern effect called "global dimming, " which relates to how increasing pollution paradoxically may be slowing global warming.

No matter how one looks at them, summer sunsets are fascinating phenomena.

For more information see "How old masters are helping study of global warming"

Photos courtesy of Duilio Zane

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