Oceans Were Hottest Ever in 2021

Photo: Image by Michael Watts from Pixabay

For the sixth year in a row, the oceans have registered a net major increase in heat storage over the previous year.

That is the conclusion of a just-published study authored by international team of researchers from China, the United States, and Italy.

According that team’s paper released yesterday in the journal Advances in Atmospheric Science, the amount of heat present in the top 2,000 meters of the ocean increased last year by 14 zettajoules – a unit of energy – over 2020’s previous record of 221 zettajoules. That measurement was determined used what is known as the IAP/CAS ocean temperature dataset.

That is a 6.3 percent increase in heat stored in the upper parts of the planetary oceans in just one year.

Global ocean heat content change trends from 1955 through 2021. The net Ocean Heat Content (OHC) anomaly, as it is called, is plotted in zetajoules on the vertical axis. Photo: "Another Record: Ocean Warming Continues through 2021 despite La Niña Conditions," published 11 January 2022, in Advances in Atmospheric Sciences.

A parallel analysis using data provided by NCEI and the National Oceanic and Atmospheric Administration (NOAA) calculated an even larger increase over 2020 in ocean heating, from 211 zettajoules to 227 as of the end of 2021. On that analysis’ basis, the amount of heat stored in the oceans was up by 16 zettajoules for a 7.6 percent increase.

To help understand the sheer magnitude of this increase, consider that the total electricity generated globally in 2021 was about 27,000 terawatt hours (TWh), where one terawatt = 10¹² watts. That is an estimate projected from Enerdata’s Global Energy Statistical Yearbook 2021. That 27,000 TWh converts to 0.1 zettajoules of energy.

That means that the 14 zettajoules increase in ocean heat absorbed in 2021 is equivalent to 140 times the entire world’s annual electrical power production.

According to the same data sets, 2019 was just slightly cooler than 2020, at 214 zettajoules according to the IAP/CAS dataset. The year 2017 came in as fourth hottest, at 202 zettajoules, followed by 2018’s 196 zettajoule increase.

With ocean heating considered one of the more important absolute measures of the seriousness of the climate crisis, scientists have worked for years to ensure the numbers are as accurate as possible. As noted in the research paper reviewing the ocean heating results explain, both the IAP/CAS and NCEI/NOAA calculations of ocean heating are gathered from an astounding array of measurement devices. These include, they note, “eXpendable BathyThermographs (XBTs), profiling floats from Argo, moorings, gliders, Conductivity/Temperature/Depth devices (CTDs), bottles, and instruments on marine mammals.”

Of these, one of the most extensive is the Argo system. An international project which has been operational for most of two decades, it consists of approximately 4,000 floating vessels which use probes submerged at depths ranging from 1,000 meters to 2,000 meters (3,280 feet to 6,562 feet) below sea level. These probes report data up to a series of satellites, which in turn aggregate and report the gathered information back down to the ground scientists.

According to this data, for 2021 the Atlantic and Southern Oceans bore the brunt of the heat increase, with all of that resulting from the continued growth in greenhouse gas emissions.

Data shows this ocean warming has continued relatively steadily since at least the 1950s. The massive heat sink of the waters managed to temporarily save the surface of the planet from heating as much as it would have otherwise, absorbing as much as 90 percent of the solar energy trapped closed to the planet’s surface by greenhouse gas emissions.

As the oceans warm, there are multiple damaging effects on the health of the planet.

Marine life of all kinds, from microscopic phytoplankton to coral reefs, the whole array of fish species, all the way up to the most massive of marine mammals, depend on a precise balance of temperatures, oxygen content, and food chain to survive. As the oceans heat, many forms of life have little choice but to attempt to migrate to cooler waters. That disrupts the food chain for those species which cannot move, such as coral reefs of which between 50 percent and 70 percent have already died to date.

As oceans warm the waters also expand, increasing sea level rise just by that expansion alone. Shorelines are under pressure because of that, causing more rapid degradation of land both above and below sea level. In regions where ice sits at the edges of continents as in Antarctica, that ice is being eroded by more active pressures from the expanding oceans as well.

The increased heat within those oceans also accelerates melting of the ice in regions such as the poles and Greenland, which then has the secondary effect of causing further sea level rise.

The oceanic heat also provides more energy to power more and faster-developing hurricanes, typhoons, and cyclones everywhere.

With 2021’s ocean heating likely slightly lower than it would have been without the presence of a significant La Niña weather pattern in much of the world, expect 2022 to be even hotter still.

The paper which presented these recent findings, “Another Record: Ocean Warming Continues through 2021 despite La Niña Conditions,” by Lijing Cheng, et. al., was published in the 11 January 2022 issue of Advances in Atmospheric Sciences.