Water has a high heat capacity – it can store and retain more heat than many other substances. Because of this, the Earth has thermal inertia – the ability to resist temperature changes. Because of its high heat capacity, the temperature of water in the ocean rises and falls only slightly – even when the ocean gives or receives significant amounts of heat.
Therefore, temperature changes in the sea are not very severe and are smoother in time. By comparison, the temperature on land in some areas can change by 20°C in a single day during certain seasons. We recommend an article about world thermostat.
The thermal inertia of the ocean is just as important for terrestrial organismsas for because a huge amount of energy comes from the sun. About half of this energy passes through the atmosphere and most of it is absorbed by the ocean.
Through convection, evaporation and radiation, heat returns to the atmosphere and is radiated back into space. The amount of heat that comes with solar radiation and from the Earth’s internal thermal sources is about equal to the amount of heat emitted into space.
The Earth is in thermal equilibrium – which means that it cools at about the same rate as it heats up. If you consider long time intervals, the Earth is neither getting substantially warmer nor colder.