One of the largest fire clouds ever recorded has been drifting around the Southern Hemisphere for over a month. Heat and freak thunderstorms generated by Australia’s massive wildfires sent ash and toxic materials high into the atmosphere, where they formed a massive dark cloud of debris. It’s been measured at 15 miles high at some points, and at one point it covered more than 1 million square miles — about half the size of Canada.
NASA has been tracking the massive cloud from space as it slowly drifted over to South America and then looped back toward Oceania where it hovered over New Zealand, turning glaciers brown, and perhaps hastening their melting.
As Australian firefighters get their blazes under control, the cloud has been dissipating. Health experts say toxic chemicals and debris eventually drop back to Earth, through the air or within raindrops, where they can be inhaled or ingested by humans and animals.
The giant cloud may also impact global weather by blocking sunlight to the Earth’s surface, an effect known as "nuclear winter," named after a hypothesis that the world would become extremely cold due to the firestorms of a nuclear war. The same effect happens in major volcanic eruptions when giant plumes of ash sweep across continents. In 1815 the Mount Tambora volcano in Indonesia created the "year without summer" across much of the globe, including in the United States, where farmers lost crops as seasonal temperatures plummeted.
Right now, scientists aren’t sure when the Australian fire cloud will dissipate or whether it will start moving again.