According to the IPCC, global mean sea level rose by about 20 cm between 1901 and 2018. And the rise is speeding up: it now approaches 4 mm a year, nearly three times the rate of the early 20th century. Two causes dominate: melting glaciers and ice sheets, and the expansion of warming water, since a warmer ocean takes up more space.
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.