Recent research led by UNSW Sydney has revealed that ocean warming rates have increased dramatically since the 1990s, with nearly a doubling of warming during 2010-2020 compared to 1990-2000. The study, published in Nature Communications, also identified the regions in the ocean that are doing the most work in heat uptake or absorption, which has implications for sea-level rise and climate impacts.
Greenhouse gas concentrations in the atmosphere from human activity trap heat within the climate system, causing the warming of air, land surface, oceans, and melting of polar ice. Oceans absorb over 90% of the excess human-generated heat accumulated in the Earth’s climate system, moderating atmospheric temperature rises. Although ocean warming helps slow the pace of climate change, it comes at a cost. The world’s oceans are now the hottest ever recorded, and heat causes water to expand and ice to melt, leading to rising sea levels. Ecosystems are also experiencing unprecedented heat stress, and the frequency and intensity of extreme weather events are changing rapidly.
Hotspots of Ocean Heat Uptake
Ocean warming has been observed across all water masses from surface to deep-sea regions, including the abyssal layers, and spanning each basin from the tropics to the polar regions. However, the distribution of ocean warming by region was far from uniform. The Southern Ocean has seen the largest increase in heat storage over the past two decades, holding almost the same excess anthropogenic heat as the Atlantic, Pacific, and Indian Ocean combined. This includes two large masses of water in the Southern Ocean that combine to fill a depth range of 300 – 1500 meters.
According to a study that evaluated all available observations of ocean warming activity spanning modern Argo float data to those taken in the 1950s when only sparse measurements were made from ship-borne devices, oceanic warming has been pervasive worldwide. The study analyzed the heat uptake across water masses and quantified each water mass’s role in ocean heat content change. The Southern Ocean saw the largest increase in heat storage over the past two decades, holding almost the same excess anthropogenic heat as the Atlantic, Pacific, and Indian Ocean combined.
The Southern Ocean has been identified as a hotspot of ocean heat uptake, with an accelerating rate of heat stress. The excess heat in the Southern Hemisphere ocean has been identified as a major contributor to global sea level rise. The researchers found that melting ice caps, extreme weather, and marine ecosystems, including coral reefs, are all highly sensitive to ocean temperature changes. It is critical to understand exactly how and where the ocean warms – both now and into the future.
The Southern Ocean is a key region for monitoring ocean heat content and heat storage. The researchers call for more international action from big-emitting nations to meet their net zero carbon targets as soon as possible and limit the damage from uncontrolled ocean warming. The team also highlights an urgent need to increase monitoring of the global oceans, especially in remote locations like the polar oceans, as well as key regions of the subtropical and coastal seas to better understand and predict sea-level rise and impacts on marine ecosystems.
The study highlights the importance of Argo floats in monitoring ocean heat content and heat uptake. Without Argo floats, the study would not have been possible. The researchers stress the need for continued investment in technology and infrastructure to monitor the global oceans and better understand the impacts of human-generated heat on ocean ventilation, overturning circulation, and global ocean salinities.