Sea surface temperature

Sea surface temperature (or ocean surface temperature) is the temperature of ocean water close to the surface. This temperature is usually measured between 1 millimetre and 20 metres below the surface. It plays a big role in changing the air close to the shore and affects weather patterns around the world.

Warm sea surface temperatures can help create and make cyclones over the ocean stronger. These temperatures also change during the day, but not as much as the air above. Coastal areas feel these changes too, with winds either bringing cooler or warmer water to nearby lands.

Because the ocean takes in most of the extra heat from climate change, sea surface temperatures have been rising. Between 1850–1900 and 2011–2020, the average temperature went up by about 0.88 °C, with much of that warming happening between 1980 and 2020. This warming affects weather and climate all over the planet.

Definitions

See also: Ocean temperature

Sea surface temperature, also called ocean surface temperature, is the temperature of the water very close to the top of the ocean. How deep this "surface" goes can change depending on how we measure it, but it is usually somewhere between 1 millimetre (0.04 in) and 20 metres (70 ft) below the actual surface of the sea.

For comparison, the sea surface skin temperature looks at the top 20 or so micrometres of the ocean's surface. Different groups, like the Intergovernmental Panel on Climate Change (IPCC), describe sea surface temperature based on how they measure it. They talk about the temperature in the top few metres of the ocean, measured by ships, buoys, and floating devices. Satellite measurements can also help, but they need to be adjusted to match the temperature measured closer to the surface.

The temperature deeper in the ocean, below the surface layer, is called ocean temperature or deeper ocean temperature. These deeper temperatures also change depending on where you are and when you measure them, and they are important for understanding how much heat the ocean holds and how the layers of the ocean arrange themselves. Both the surface and deeper ocean temperatures are getting warmer, which is one way climate change is affecting the oceans.

Variations and changes

Local variations

See also: Upwelling

The temperature of the ocean near the surface changes a little each day, just like the air above it, but not by much because water takes longer to heat up or cool down. On very calm days, the ocean's surface temperature can change by about 6 °C (10 °F). In some places, like the Aral Sea, the water temperature near the bottom is warmest in December and coolest in May and June. Winds near the coast can push warm surface water away and bring up cooler water from below, which helps sea creatures by bringing more food. After strong storms or when dust from places like the Sahara crosses the ocean, the surface temperature can drop a little.

The tropical parts of the ocean have been warming up faster than other areas since 1950, especially in the Indian Ocean and the western Pacific Ocean.

Atlantic Multidecadal Oscillation

Ocean currents, like the Atlantic Multidecadal Oscillation, can change sea surface temperatures over many years. These changes in temperature in the North Atlantic can affect weather patterns far away, including in the North Pacific.

Regional variations

Main article: El Niño-Southern Oscillation

El Niño happens when the ocean temperature in the central and eastern Pacific gets warmer than usual for many months. This warm water changes weather patterns, causing dry conditions in some places and heavy rain in others. It can also affect fishing because the warm water does not have as many nutrients as the cooler water it replaces.

Recent increase due to climate change

Further information: Effects of climate change on oceans § Rising ocean temperature

Scientists believe that all parts of the ocean will get warmer by the year 2050. They think the temperature will rise by about 0.86 °C to as much as 2.89 °C depending on how much greenhouse gases we release into the air. A study from 2025 found that the rate of warming in the ocean has increased a lot over the past few decades and expect it to keep speeding up.

Measurement

There are many ways to measure the temperature of the ocean's surface, and each method can give slightly different results. Scientists often note exactly how deep the measurement was taken because temperatures can change with depth, especially during the day when the sun heats the surface.

One of the oldest ways to measure this temperature was using a special glass thermometer, first done by Benjamin Franklin on ships. Later, people dipped thermometers into buckets of seawater. Today, some ships measure the temperature using sensors near their engine intake, though this can make the reading a little too warm.

Fixed weather buoys about 3 metres deep also measure the temperature. Many floating buoys around the world send their data to satellites. In the United States, a network of coastal buoys helps collect this information.

Since 1967, weather satellites have helped scientists learn about ocean temperatures from space. These satellites look at the heat coming from the ocean’s surface and can show how temperatures change over large areas and time. However, satellite measurements can be tricky because they only see the very top layer of the ocean and can’t see through clouds.

Importance to the Earth's atmosphere

See also: Air mass, Numerical weather prediction, Precipitation (meteorology), and Effects of climate change on oceans

The temperature of the ocean's surface plays a big role in shaping the air above it. This makes it very important for weather forecasts. Warm ocean water helps create things like sea fog and breezes. It can also change the air nearby, sometimes leading to snow bands when cold air moves over warm water.

Tropical cyclones

Main articles: Tropical cyclogenesis and Tropical cyclones and climate change

For tropical storms, or hurricanes, warm ocean water is a key ingredient. The water needs to be at least about 26.5 °C (79.7 °F) to help these storms form and stay strong. This warmth gives the storm its energy. Sometimes, even if the water isn't quite this warm, storms can still develop under the right conditions, like when the air higher up is cooler or more moist.