How one eruption can make the whole planet colder, and the year summer never came.
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On 15 June 1991, Mount Pinatubo in the Philippines exploded. It was the second-biggest eruption of the 1900s. Its cloud of ash and gas shot 35 km up: four times higher than Mount Everest!
Almost all our weather happens in the lowest layer of the air. Pinatubo blasted gas right through it, into the dry stratosphere above. There, over a few weeks, the gas turned into tiny droplets.
Now it’s your turn. Drag the slider to erupt Pinatubo, then follow its droplet cloud over the next three years. (The yellow streaks are drawn by hand, and they move much faster than the real cloud.)
The droplets bounce some sunlight back into space, like a thin sunshade round the Earth. So for about two years, the world was about half a degree cooler on average (blue, drawn simply). That’s the opposite of El Niño, which can make the whole world hotter for a while.
In April 1815, Mount Tambora, on the island of Sumbawa in Indonesia, exploded. It was the biggest eruption in recorded history. It blew away so much rock that the mountain ended up more than a kilometre shorter!
In parts of Europe and in North America, the next year, 1816, became known as “the year without a summer” (blue, drawn simply). Snow fell in New England in summer, and crops failed. Food ran short, and people went hungry in many lands.
Could a big eruption cancel out global warming? No: its droplets fall out of the sky after a few years, and the cooling ends with them. Volcanoes also breathe out carbon dioxide, the gas that traps heat, but all of them together make less than 1% of what people do.
Tambora is on Sumbawa, a small island in Indonesia. Go east from Java, past Bali and Lombok.
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The globe pictures are simplified to show the idea. Earth images: NASA Blue Marble (public domain).