A new study published on 1 November in the journal Nature suggests the oceans are heating up much faster than expected (1). The study, led by Laure Resplandy, a biogeochemical oceanographer at Princeton University, shows that ocean warming between 1991 and 2016 was, on average, 60 per cent more per year than previous estimates. Importantly, this implies the Earth that overall the Earth is more sensitive to climate change than previously thought.
Heat uptake by oceans has traditionally been quantified using hydrographic temperature measurements and data from the Argo float program, an international cooperation to measures various properties of the Earth’s oceans, including temperature, salinity, and currents. The dataset used in the study has been collected by the Scripps Institution of Oceanography for unrelated reasons since 1991.
In this report, the researchers provide an independent estimate based on atmospheric oxygen (O2) and carbon dioxide (CO2) measurements as a “whole-ocean thermometer.” The amount of gases the ocean can hold depends on its temperature; therefore, as O2 and CO2 levels increase, the ocean warms and releases these gases. In other words, the ocean is essentially pushing out more O2 and CO2.
This new approach has not been fully vetted just yet. Moreover, the method is better suited to long-term measurements and is not appropriate for short-term estimates, for example, it cannot be used to study the changes year-on-year. Nonetheless, the complementary approach provides important new evidence that previous estimates were too low―the United Nations Intergovernmental Panel on Climate Change (IPCC) estimated that oceans were taking up around 8 zetajoules of heat (energy), but the new predictions are closer to 13 zetajoules. To put this into perspective, the total world consumption of energy is about half a zetajoule annually, according to the International Energy Agency.
We know the oceans play a crucial role in the global climate by absorbing excess heat from the atmosphere―oceans may store as much as 90 per cent of additional heat being produced by global warming. But just how quickly the oceans are warming remains a topic of debate. More accurate measurement of the rate of ocean warming could help scientists to better predict the future effects of climate change.
A major report released by the IPCC in October highlights the effects climate change could have by 2040 if human greenhouse gas emissions continue at current levels, including an increase in flooding, food shortages, and loss of biodiversity. They concluded that to meet the 1.5 C threshold outlined in the Paris Climate Pact, an “unprecedented” effort from world leaders will be required in order to achieve net-zero carbon emissions by 2050. Unfortunately, these new findings are yet more evidence that global warming over the past few decades may be more closely aligned with worst-case scenarios. The estimate simply validates warnings that humanity has only a short period of time to ward off some of the most catastrophic effects of global warming.
(1) Resplandy, L. et al. Quantification of ocean heat uptake from changes in atmospheric O2 and CO2 composition. Nature (2018). DOI: