365 Days of Climate Awareness 95 – The Heat Content of the Ocean

Ocean water has a specific heat of 4.184 J/g°C (kilojoules per gram-degree Celsius), meaning 4.184 Joules of heat energy must be added to one gram of seawater to raise its temperature by one degree Celsius. This is slightly higher than fresh water’s specific heat of 3.898 J/g°C. The very high heat capacity of water—greater than metals like copper and lead—makes it ideal as a temperature buffer for the planet, being able to remain in its liquid phase despite huge swings in heat content.

Ocean heat content, 200-2020.

Our ability to measure temperature in the ocean, and with that to estimate its heat content, has improved to an incredible degree over the last thirty years. Satellites track sea surface temperature on a global scale. Moored buoys, at different depths, record local conditions around the world. Subsurface drifting buoys record temperature and other properties while pushed along by currents (plots of their tracks are called, with perfect deadpan humor, “spaghetti diagrams”).

Ye Olde Spaghetti Diagramme.

With all these data streams we can assemble a more complete temperature profile, and heat content estimate, of the entire global ocean than ever before. And this is of grave importance to climate science, since water by volume has a heat content roughly 3,000 times greater than air. The ocean’s ability to absorb heat is finite, like its ability to absorb CO₂.

The warming of the oceans is having a virtually unlimited number of effects. Among the largest are increased melting of ice shelves (marine glaciers) and sea ice, sea level rise, increased evaporation leading to increased precipitation and storm strength globally, the possible impending release of methane from submarine permafrost, and ecosystem impacts such as coral die-offs. It is only in recent decades that we have developed anything like a comprehensive view of the internal heat state of the world ocean.

Since the 1930’s ocean heat level has increased immensely, by roughly an order of magnitude (factor of ten), from about 50 ZJ (Zettajoules, 1x10²¹ joules) to nearly 500 ZJ.

Tomorrow: changes in ocean salinity.

Be brave, and be well.