The ocean鈥檚 ability to absorb heat into its depths appears to be rapidly declining, leading to prolonged marine heatwaves, increased ocean warming and greater stress on marine ecosystems. The loss of this vital cooling mechanism suggests we could be entering a new phase of climate change.
at Yonsei University in Seoul, South Korea, and his colleagues used satellite data spanning four decades to track how sea surface temperatures (SSTs) have evolved over time.
The team was shocked at the scale of the changes and says there appears to have been a fundamental shift in the capacity of the ocean to mitigate global warming. Until this point, 90 per cent of the planet鈥檚 excess heat due to greenhouse gas emissions has been drawn down into the ocean, but the researchers warn that as the ocean becomes less successful at regulating temperature, there may be an acceleration of warming effects.
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鈥淲e were surprised by not only this increase in SST persistence, but the magnitude and widespread nature of the trend,鈥� says Song. 鈥淭he fact that this change is happening globally and in nearly all major ocean basins highlights a fundamental shift in how the ocean regulates temperature anomalies.鈥�
Of particular concern is the fact that periods of higher ocean temperature appear to be getting longer. 鈥淲e found that SST anomalies are persisting longer than before, meaning that the ocean is holding onto heat anomalies for extended periods,鈥� says Song. 鈥淭his trend has been increasing globally over the past 40 years. Additionally, this longer 鈥榤emory鈥� of ocean temperatures is linked to the increasing duration of marine heatwaves.鈥�
For example, the researchers found that in the eastern North Pacific, the average length of heat anomalies has been increasing at a rate of 2.5 days per decade 鈥� a 50 per cent rise over the past 42 years.
Song says it appears that the world鈥檚 oceans are losing their ability to dissipate heat from the surface into the deep ocean. 鈥淎s a result, heat anomalies persist longer, leading to prolonged marine heatwaves,鈥� he says. 鈥淭his could result in more frequent coral bleaching, fishery disruptions and changes in ocean circulation. Additionally, if the ocean holds on to heat for longer periods, it could reduce its ability to absorb excess atmospheric heat, potentially amplifying global warming.鈥�
鈥淭his could be a very important result. If the heat memory of the ocean is increasing, it would mean marine heatwaves are going to get longer, and that鈥檚 going to have major impacts on biology,鈥� says at the University of New South Wales in Sydney, Australia.
Nature Climate Change
