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Climate Change: Ocean Heat Uptake Much Higher than Estimated

New study suggests that seas have absorbed 60% more heat in the past 25 years than previously thought

Photo by Sebastian Voortman (Pexels)

by Anton Kuech

The oceans play a vital role in stabilizing the Earth’s climate system by functioning as the largest solar energy absorbers on the planet. Greenhouse gas emissions prevent heat from escaping into space and, as a result, most heat is stored in the upper ocean. This heat energy eventually leaves the ocean systems by evaporating water, melting ice shelves, or by direct heating of the atmosphere and thus, increasing heat content can significantly contribute to global warming for decades after absorption.

The latest major summary for policymakers by the Intergovernmental Panel on Climate Change (IPCC) described the excess energy stored in the oceans from 1971 to 2010 to be more than 90%.

Previous studies on ocean heat uptake have been using hydrographic temperature measurements and data from the Argo float program. This method has great uncertainties, because of the limited coverage of the Argo float program before 2017.  The new study, published in the journal Nature, provides an independent estimate by using measurements of atmospheric oxygen and carbon dioxide as an index of ocean warming, given the increasing release of the gases as the ocean warms. The researchers found that the oceans have gained 13 zettajoules of heat energy per year between 1991 and 2016, equivalating to around 150 times the electricity production by humans per year.  

These results show that the oceans have absorbed 60% more heat than previous studies have identified and, therefore, carry serious implications for further decision-making in response to climate change mitigation. Rising ocean temperatures will have serious knock-on effects for many marine species and ecosystems. The pressure on already endangered ecosystems, such as coral reefs, will increase and detrimental events like coral bleaching and the subsequent loss of breeding environments for marine fish and mammals will be a consequence. The increasing prevalence of extreme weather events, faster and increased sea ice melting, as well as a stronger sea level rise, are expected as a result, affecting not only animals but also humans around the world. The study’s author, Laure Resplandy, stated: “The result suggests that ocean warming is at the high end of previous estimates, with implications for policy-relevant measurements of the Earth’s response to climate change.” Another possible result could be changes to ocean currents, whereby a weakening of the thermohaline circulation could lead to dramatic climate cooling, a theory assessed in a 2004 study (Hansen et al.), which suggested a prospective weakening of the circulation leading to cooling in Northern Europe, although the study concluded that we would not quite face the doomsday scenario portrayed in the science-fiction disaster film The Day After Tomorrow.

These far-reaching findings come months after the landmark report by the UN Intergovernmental Panel on Climate Change (IPCC) was released. The UN report gave clear warning signals to its members, concluding that humanity has 12 years to act to avoid reaching the global warming temperature of 1.5C, beyond which disastrous effects of climate change on nature will have irretrievable consequences. When taking into account the new findings on heat absorption by the sea, figures must be corrected to report the worst possible outcome.


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