The ocean absorbs about a quarter of the CO₂ we emit each year, which slows warming. But as the gas dissolves, it forms carbonic acid. Surface pH has dropped from about 8.2 to 8.1, a change that looks tiny but means roughly 30% more acidity, because the scale is logarithmic. Shellfish and corals find it harder to build their limestone skeletons.
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.