Sea level is measured two ways. Tide stations record the water height along coasts relative to the land, and some records go back more than 200 years, while satellites measure the average height of the whole ocean.
Sea level rise is not the same everywhere, because local factors such as sinking land, ocean currents, and land still rebounding after the weight of Ice Age glaciers can make a place's sea level rise faster or slower than the global average.
As of November 2026, melting ice on land is now the main source of added water in sea level rise, and NASA reports that melting land ice from Greenland and glaciers accounts for about two-thirds of sea level rise to date.
As of November 2026, the ocean has absorbed about 90 percent of the extra heat that people's greenhouse gas emissions have trapped on Earth since 1971.
The ocean has taken in a large share of the carbon dioxide people release, and without that, the amount in the air would be even higher. How well the ocean can keep doing this is one of the big unknowns about the greenhouse effect.
Water heated by magma under the seafloor picks up metals such as iron, zinc and copper. Where this fluid meets cold sea water, minerals form black chimneys called black smokers. The fluid can reach 400 degrees Celsius (750 degrees Fahrenheit) without boiling because of the deep ocean's pressure.
Trenches make up the deepest 45 percent of the ocean's depth range, but the very deepest parts are only about 1 percent or less of a trench's area, and most of a trench is its steep slopes and walls.
Dead zones are ocean areas with too little oxygen for most sea life. They can form when an algal bloom dies and the microbes that break it down use up the oxygen faster than it can be replaced.
Marine snow is a mix of dead plankton, waste and mucus that slowly sinks from the surface. It carries carbon to the deep sea, and scientists still do not fully understand how much.
When stressed by changes in temperature, light or nutrients, corals expel the algae that live in their tissues and turn white. One idea about why is that stressed corals make too much of a chemical called superoxide.
Words to know
- rebounding: rising back up
- satellites: orbiting machines
- magma: melted rock
- superoxide: a reactive chemical
- mucus: slimy coating
