The smoke from wildfires was bad here last summer but it didn’t actually get dark in the afternoon. Stinky and unhealthy, yes, but dark, no. São Paulo on the other hand…

In the middle of the afternoon on August 19th South America’s largest city went dark. Under a thick, black cloud at 3pm, the lights flickered on in São Paulo’s skyscrapers; on the motorways brake lights started to glow in the city’s bumper-to-bumper traffic, and many Paulistanos were worried. Social-media users posted pictures of the gloom, juxtaposing the dystopian afternoon sky with fictional apocalyptic places such as Gotham City from “Batman”, Mordor from “Lord of the Rings” and “the upside down” from “Stranger Things”.

Meteorologists scrambled to explain what was going on. But the most likely explanation, most accept, is that fires burning far away in the rainforest are to blame. Climatempo, a popular private meteorology website, reported that a cold front brought low-lying clouds which then combined with smoke to form the thick black smog.