Thanks to satellites and supercomputers, a six-day forecast today is as reliable as a five-day forecast was ten years earlier, according to a 2015 review in Nature. But a wall remains: the atmosphere is chaotic, as Edward Lorenz showed in the 1960s. Beyond about two weeks, a tiny error is enough to make any detailed forecast meaningless.
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.