Sea surface temperature

Sea surface temperature (or ocean surface temperature) is the temperature of ocean water close to the surface. The exact meaning of surface varies in the literature and in practice. It is usually between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface. Sea surface temperatures greatly modify air masses in the Earth's atmosphere within a short distance of the shore. The thermohaline circulation has a major impact on average sea surface temperature throughout most of the world's oceans.

Warm sea surface temperatures can develop and strengthen cyclones over the ocean. Tropical cyclones can also cause a cool wake. This is due to turbulent mixing of the upper 30 metres (100 ft) of the ocean. Sea surface temperature changes during the day. This is like the air above it, but to a lesser degree. There is less variation in sea surface temperature on breezy days than on calm days.

Coastal sea surface temperatures can cause offshore winds to generate upwelling, which can significantly cool or warm nearby landmasses, but shallower waters over a continental shelf are often warmer. Onshore winds can cause a considerable warm-up even in areas where upwelling is fairly constant, such as the northwest coast of South America. Coastal sea surface temperature values are important within numerical weather prediction as the sea surface temperature influences the atmosphere above, such as in the formation of sea breezes and sea fog.

It is very likely that global mean sea surface temperature increased by 0.88 °C between 1850–1900 and 2011–2020 due to global warming, with most of that warming (0.60 °C) occurring between 1980 and 2020. The temperatures over land are rising faster than ocean temperatures. This is because the ocean absorbs about 90% of excess heat generated by climate change.

Sea surface temperature (SST), or ocean surface temperature, is the water temperature close to the ocean's surface. The exact meaning of surface varies according to the measurement method used, but it is between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface.

For comparison, the sea surface skin temperature relates to the top 20 or so micrometres of the ocean's surface.

The definition proposed by Intergovernmental Panel on Climate Change (IPCC) for sea surface temperature does not specify the number of metres but focuses more on measurement techniques: Sea surface temperature is "the subsurface bulk temperature in the top few metres of the ocean, measured by ships, buoys and drifters. [...] Satellite measurements of skin temperature (uppermost layer; a micrometre thick) in the infrared or the top centimetre or so in the microwave are also used, but must be adjusted to be compatible with the bulk temperature."

The temperature further below that is called ocean temperature or deeper ocean temperature. Ocean temperatures (more than 20 metres below the surface) also vary by region and time, and they contribute to variations in ocean heat content and ocean stratification. The increase of both ocean surface temperature and deeper ocean temperature is an important effect of climate change on oceans.