Water on Earth serves many purposes for sustaining life. Among these, temperature regulation is probably the most important. Just as water is an important component in regulating the temperature of any endothermic organism, it also regulates the temperature of the Earth.
The secret to water’s effect on temperature lies in its abundance and density, as well as its evaporative properties. Essentially, ocean currents transfer thermal energy from regions near the equator to areas of higher latitude. Water also absorbs thermal energy during the day and releases it at night, ensuring that the temperature difference between night and day remains relatively small. The deeper the water, the less it tends to change, thus only the top few feet of water are significantly heated by a day’s sunshine, while the deep sea currents tend to maintain a very steady temperature.
Oceanic currents are convection currents driven by the centripetal force of Earth’s rotation and the thermal effects of the Sun. These seemingly insignificant forces are actually strong enough to produce a very fast, constant current in every ocean on the planet. Coincidentally, the heat that drives the current is the same heat that warms the otherwise cold areas of the planet.
Without explaining molecular thermodynamics in too much depth, this is basically how oceanic currents work and how they regulate climate and weather. Currents carry heat from one place to another. If it weren’t for these phenomena, coastal regions would experience the same weather as landlocked desert regions.