Permafrost, ground that stays frozen year-round across nearly a quarter of the Northern Hemisphere's land, locks away plant and animal remains built up over millennia. It is estimated to hold about 1,500 billion tonnes of carbon, roughly twice as much as the atmosphere. As it thaws, this material decomposes and can release CO₂ and methane, amplifying warming.
On 27 August 1883, the eruption of the Indonesian volcano Krakatoa was heard as far away as Rodrigues Island, nearly 4,800 km away. Its pressure wave was picked up by barometers worldwide and circled the globe several times. The tsunamis that followed killed more than 36,000 people.
The deepest known point in the ocean, Challenger Deep, lies roughly 10,900 m below the Pacific surface. Drop Everest in and its summit would still sit about 2 km underwater. Down there, the pressure is more than 1,000 times what you feel at sea level, roughly a tonne pressing on every square centimetre.