Ocean Observation

Measuring ocean temperature and chemistry is no simple task: the ocean is vast and deep, and it is not the same everywhere. But by drawing on a variety of tools, scientists are slowly developing a better picture of how the ocean is changing and how it might continue to change in the future.

How is climate change affecting the ocean?

Scientists studying the ocean's present and past temperature and chemistry have some answers.

• As a whole, the ocean is warming: Over the past 50 years, the top 700 meters (about 2,300 feet) of the ocean has warmed about 0.10ºC (0.18ºF)—less than the temperature increase in the atmosphere. Why the difference? Water warms more slowly than air, which means that the ocean will continue to warm until it reaches a temperature balance with the atmosphere.
• Certain parts of the ocean have actually cooled: Parts of the North Atlantic and the central North Pacific have cooled over recent decades. Natural variation in ocean circulation may have brought cooler waters to those regions, even as the ocean as a whole was warming.
• The ocean is acidifying: Increased CO₂ dissolved in the ocean has caused the surface pH to drop by about 0.15 units since about 1750.

Seen From Ships

Ships traveling between the continents have long been one of the best sources for information about the ocean. Many ships measure water temperature and chemistry as they pass through the ocean, take samples back to labs for further analysis, or drop devices that record water temperature and chemistry over days, months, or years.

Sea From Above

Ships do not cover every inch of the ocean—in fact, most only travel along narrow shipping lanes. To take global ocean measurements, scientists now also rely on satellites that record sea surface height and temperature.

Buoy Network Satellite observations give a good overall sense of surface ocean temperatures, but for more detailed information about temperatures below the surface, as well as ocean chemistry, many scientists rely on floats regularly spaced around the globe. Such devices, like the buoy here, can be outfitted to measure temperature, pH, salinity, or CO₂ content.

The Next Generation

Buoys and floats are more or less fixed in space: some can move up and down, but all are anchored in one spot. Ocean gliders like this one, however, can be programmed to travel for up to five weeks at a time, usually along coastlines, surfacing periodically to transmit data. They propel themselves through the ocean by changing their buoyancy, moving up and down through the water column in a sawtooth pattern.