Where Does Ocean Heat Come From?

First, do we really know the temperature and thus heat content of the ocean?

The ocean is vast and covers ~70% of the Earth’s surface, making it the largest system on the planet. Despite its size, only a small portion of the ocean has been explored and mapped in detail.

It is estimated that <20% of the world’s oceans have been mapped and explored to date. [emphasis, links added]

This is largely due to the difficulties and challenges associated with ocean exploration, such as the high pressure and extreme environments found in the deep ocean, as well as the high cost of research vessels, equipment, and technology.

Most of the ocean that has been explored in detail is located near the coasts or in shallow waters, where it is more accessible to research vessels and equipment, but usually far away from the heat sources of mid-ocean ridges.

The deep ocean, which makes up the majority of the ocean’s volume, remains largely unexplored, with less than 5% of the ocean floor having been mapped in high resolution.

Advances in technology, such as underwater drones and submersibles, are helping to improve our understanding of the ocean and its ecosystems, and it is likely that our knowledge of the ocean will continue to expand in the coming decades.

Temperature measurements in the ocean are typically taken using a variety of instruments. These instruments can be deployed from research vessels or from moored or drifting buoys, and they collect temperature data at different depths throughout the ocean.

The amount of the ocean that is measured for temperature varies depending on the method of measurement and the specific objectives of the research.

However, it is estimated that significantly less than 10% of the world’s oceans have been sampled for temperatures at depths greater than 2,000 meters.

Despite the relatively limited coverage of temperature measurements in the deep ocean, there are ongoing efforts to improve our understanding of the ocean’s temperature structure and variability.

For example, the Argo program deploys thousands of autonomous floats that measure temperature and other oceanographic variables throughout the world’s oceans.

The Argo program is a global network of robotic floats [pictured above] that measure temperature, salinity, and other properties of the ocean.

These floats, which are deployed from ships and drift with ocean currents, provide real-time data on the state of the ocean and its variability, which is used for climate research, weather forecasting, and oceanographic studies.

The Argo fleet currently consists of more than 4,000 floats that are deployed throughout the world’s oceans, covering all ocean basins from the polar regions to the tropics.

In addition to the buoys, there are approximately 2k other measurement stations. Let’s assume each measurement is accurate to a 1km diameter around the place of the measurement.

That is .0001% of the ocean surface that is accurately measured for temperature.

Despite this limited data, climate scientists claim that ocean heat content is increasing.

So, where does ocean heat come from?

Heat is added to the ocean through the crust primarily through a process called hydrothermal circulation, which occurs when seawater seeps down into cracks and fissures in the ocean floor and is heated by the magma and hot rocks beneath the crust.

The heated water then rises back to the surface, carrying heat and minerals with it.

It is estimated that hydrothermal vents add around ~40 terawatts of heat to the ocean, which is equivalent to the heat generated by around ~100,000 average-sized power plants.

However, it is important to note that this heat is not evenly distributed throughout the ocean and is concentrated in specific areas where hydrothermal vents are present.

Additionally, it is worth noting that while hydrothermal circulation is an important source of heat for the ocean, it is not the only one.

The sun also provides a significant amount of heat through solar radiation, which drives ocean currents and contributes to the ocean’s overall heat budget.

The amount of heat that is added to the ocean through the Sun varies depending on several factors, including the time of day, latitude, season, cloud cover, and atmospheric conditions.

However, on average, the Sun is estimated to add about 168 watts per square meter of heat to the Earth’s surface.

A significant portion of this solar energy is absorbed by the oceans, which store a large amount of heat due to their high heat capacity.

While the Sun is a major source of heat for the ocean, it is worth noting that other factors also contribute to ocean heating and cooling, including ocean currents, winds, and atmospheric processes.

In addition, changes in the amount of solar radiation that reaches the Earth’s surface, such as those caused by variations in the Earth’s orbit and tilt, can also affect the amount of heat that is added to the ocean over long timescales.

The amount of heat that has been added to the ocean as a result of increasing atmospheric carbon dioxide (CO2) concentrations is commonly referred to as the “ocean heat uptake” or “ocean heat content.”

This is the amount of heat energy that has been absorbed by the ocean from the atmosphere due to the increased greenhouse effect caused by rising CO2 levels.

According to the IPCC, the ocean has absorbed more than 90% of the excess heat that has been trapped in the Earth’s climate system as a result of human activities since the 1970s.

This ocean heat uptake is estimated to be around 0.5-1 watts per square meter of the Earth’s surface, on average, over the period from 1971 to 2018.

In summary, heat entering the oceans is a complicated mix of crustal, solar, and atmospheric phenomena and our limited data means that we don’t know where and in what proportions heat is entering the ocean system.

The common assumption that it is all attributed to increases in anthropogenic GHG emissions presumes that we understand heat flow into the oceans and brings to mind a famous quote from Mark Twain:

“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.”

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