WATCH | You can't set fire to ice? You know nothing Jon Snow
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Can you set fire to ice? Turns out you can if the ice is from the ocean floor.
This is because the ice contains methane, which burns quite readily.
Methane doesn't dissolve in water. It just bubbles through it, unless that water is either very cold, or under a lot of pressure. This makes the molecular composition of the ice form a sort of cage that can trap the methane molecules, which gives you methane hydrate.
Some countries like Japan see this as a great source of natural gas, which burns cleaner than most other fossil fuels.
Methane is actually a more powerful greenhouse gas than CO2. Fortunately, most of this ice is trapped deep in the ocean and seems pretty stable. Any methane that is released is normally eaten by bacteria.