Ocean Warming
90%
of the extra heat remaining on the planet is stored in the ocean.
Schematic presentation of how much heat is remaining on Earth and where is stored for the current human-driven global warming (2006-2020 and 1971-2020). Source: von Schuckmann et al. 2023.
Incoming and outgoing solar radiation are naturally balanced on Earth. Some phenomena can change the energy exchange and cause the Earth to store more heat than it can release back into space.
The greenhouse gas effect, caused by human activities, prevents heat from escaping the Earth, causing an increasing warming of the planet. The surplus heat remaining is stored by the different planetary systems – the atmosphere, the land, the cryosphere and the ocean.
The ocean has the incredible capacity to absorb heat. From the extra heat remaining on Earth, around 90% is stored in the ocean, redeeming the surface of the planet from a much violent warming, but condemning the marine environment to impacts for thousands of years.
How is the ocean warming?
The ocean has been warming for as long as we can measure it – at least since the 1960’s.
Between 1960 and 2023 scientists have observed that the global ocean until 2000 metres of depth has warmed on average 0.58 ± 0.13 Wm−2. However, in the last two decades, the ocean has warmed almost twice as fast – at an average rate of 1.05 ± 0.17Wm−2.
Ocean heat content for the global ocean up to 2000m below ocean surface between 1960 and 2023 using different estimates. The energy absorbed by the ocean is measured in Joules/square metre (J/m2). Source: Copernicus Marine Ocean State Report 8.
Why Ocean warming matters?
Increasing sea water temperatures is leading to many changes, not only in the ocean but on the whole planet. A warmer ocean is causing sea levels to rise and sea ice to melt, is leading to more frequent, more intense, more spread-out and longer-lasting marine heatwave events. A warmer ocean is also influencing water stratification (separation into layers) and nutrient distribution, the loss of oxygen in marine ecosystems, and fuelling storms and altering weather patterns.
How is Ocean heat measured?
Ocean heat can be quantified directly and indirectly. Direct measurements (in situ) of ocean heat are nowadays often collected by autonomous devices deployed around the world, such as the Argo floats, which collect data on the temperature of the water column up to 2000 metres. Indirectly, the ocean heat content can be estimated using satellite measurements of the ocean’s thermal expansion.
Estimates of the ocean heat content in the past (reanalysis) are used to derive trends and help understand long-term changes (climate change).
Monitoring Ocean warming
Notes and references:
von Schuckmann, K., et al., 2020: Heat stored in the Earth system: where does the energy go? Earth System Science Data. 12 (3). 2013-2041. https://doi.org/10.5194/essd-12-2013-2020
Cheng, L., G. Foster, Z. Hausfather, K. E. Trenberth, and J. Abraham, 2022: Improved Quantification of the Rate of Ocean Warming. J. Climate, 35, 4827–4840, https://doi.org/10.1175/JCLI-D-21-0895.1.
Minière, A., et al., 2023: Robust acceleration of Earth system heating observed over the past six decades. Sci Rep 13, 22975. https://doi.org/10.1038/s41598-023-49353-1