Post-human sunsets

Long after the microscopic soot from human pollution has been flushed out of the air, when only the greenhouse gases remain to heat up the seas, what would sunsets be like? We got a look at that during this nearly rain-free week in Mumbai. It was so spectacular that The Family changed the time of her daily walk to synchronize with the sunset. Cameras rarely see what the human eye does, but you may still get a sense of what we have been seeing in the slideshow below.

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Soot and other particles in the air are relatively large, and serve only to dim the colours of the sunset. The colours are brighter when they have settled out of the air. Normally we see these monsoon sunsets at most for a day after heavy rains, before traffic pumps particles into the air and obscures them. Now we can see it for days on end. I understand now why people are calling this time the anthropause.

In cold and dry air, the colour of the sunset comes from sunlight scattered by molecules of air. The result is a gentle wash of light, changing colour from east to west, and intensity in the north-south angle from the sun. The sunset colours of tropical monsoons come from a more complex process: the sunlight scattering from aerosol droplets of moisture in the air. This explanation can be developed using a scheme invented by Gustav Mie. I wonder if he saw colours such as this during his youth in the German port of Rostock.

In any case, we are seeing the sunsets on a hot and wet earth, free of ongoing industrial pollution. These are the colours of the postanthropic world.