Ocean heat content

Ocean heat content (OHC) is the energy absorbed and stored by oceans. To calculate the ocean heat content, measurements of ocean temperature at many different locations and depths are required. Integrating the areal density of ocean heat over an ocean basin, or entire ocean, gives the total ocean heat content. Between 1971 and 2018, the rise in OHC accounted for over 90% of Earth’s excess thermal energy from global heating. The main driver of this OHC increase was anthropogenic forcing via rising greenhouse gas emissions. By 2020, about one third of the added energy had propagated to depths below 700 meters. In 2022, the world’s oceans, as given by OHC, were again the hottest in the historical record and exceeded the previous 2021 record maximum. The four highest ocean heat observations occurred in the period 2019–2022 with the North Pacific, North Atlantic, the Mediterranean, and the Southern Ocean all recording their highest heat observations for more than sixty years. Ocean heat content and sea level rise are important indicators of climate change. Ocean water absorbs solar energy efficiently and has far greater heat capacity than atmospheric gases. As a result, the top few meters of the ocean contain more thermal energy than the entire Earth's atmosphere. Since before 1960, research vessels and stations have sampled sea surface temperatures and temperatures at greater depth all over the world. Furthermore, since the year 2000, an expanding network of nearly 4000 Argo robotic floats has measured temperature anomalies, or the change in OHC. OHC has been increasing at a steady or accelerating rate since at least 1990. The net rate of change in the upper 2000 meters from 2003 to 2018 was +0.58W/m2 (or annual mean energy gain of 9.3 zettajoules). The uncertainty is primarily due to the challenges of making multidecadal measurements with sufficient accuracy and spatial coverage. Changes in ocean heat content have far-reaching consequences for the planet's marine and terrestrial ecosystems; including multiple impacts to coastal ecosystems and communities.