‘Deep ocean’ water more than 2,300ft below the surface will warm by a further 0.36°F in the next 50 years as it continues to absorb ‘excess heat’ created by humans, scientists predict
- Oceans have absorbed about 90 per cent of the warming caused by humans
- Much of this heat is stored in the ‘deep ocean’ – 2,300ft below the surface
- Study found 62% of the warming from 1850 to 2018 is held in the deep ocean
- Temperature increase could devastate ecosystems and raise sea levels
The deep ocean could warm by a further 0.36°F (0.2°C) in the next 50 years, as it continues to absorb the vast majority of ‘excess heat’ created by humans, a new study warns.
Oceans have already absorbed about 90 per cent of the warming caused by humans since the Industrial Revolution began.
Much of this heat is stored in the ‘deep ocean’ – defined as water more than 2,300ft (700m) below the surface.
The resulting underwater temperature increase could cause sea levels to rise and have devastating consequences for ecosystems, the researchers from the University of Exeter and the University of Brest warn.
Deep-sea plants and animals which depend on oxygen may no longer be able to survive, and the change will also affect the sea’s currents and chemistry.
Much of the ‘excess heat’ stored in the subtropical North Atlantic is in the deep ocean, below 2,300ft, new research suggests.
‘As our planet warms, it’s vital to understand how the excess heat taken up by the ocean is redistributed in the ocean interior all the way from the surface to the bottom, and it is important to take into account the deep ocean to assess the growth of Earth’s “energy imbalance”,’ said Dr Marie-José Messias, from the University of Exeter.
‘As well as finding that the deep ocean is holding much of this excess heat, our research shows how ocean currents redistribute heat to different regions.
‘We found that this redistribution was a key driver of warming in the North Atlantic.’
For the study, researchers looked at a system of currents in the subtropical North Atlantic (25°N) known as the Atlantic Meridional Overturning Circulation (AMOC).
AMOC works like a conveyer belt, carrying warm water from the tropics north – where colder, dense water sinks into the deep ocean and spreads slowly south.
They used temperature records and chemical ‘tracers’ – compounds whose make-up can be used to discover past changes in the ocean, to measure levels of warming.
They found 62 per cent of the warming in the region from 1850 to 2018 is held in the deep ocean, which lies more than 700m below the surface.
AMOC works like a conveyer belt, carrying warm water from the tropics north – where colder, dense water sinks into the deep ocean and spreads slowly south. Graphic shows surface currents carrying heat towards the poles (red line) and the North Atlantic Deep Water and Antarctic Bottom Water formation sites (yellow dots) where surface waters loose buoyancy, downwell, and subsequently feed the deep (blue) and bottom (purple) return flows
These findings show warming and its effects can be transferred from one region to another.
Dr Messias said excess heat from the Southern Hemisphere oceans is becoming important in the North Atlantic – now accounting for about a quarter of excess heat.
The findings were published in the journal Communications Earth and Environment.
The new research comes after a report by Monterey Bay Aquarium earlier this year revealed that more than half of the surface of the world’s oceans have experienced excessively warm temperatures since 2014.
The researchers, who analysed a century-and-a-half’s worth of global marine temperature data, warned that extreme marine heat is now the ‘new normal’.
They added that extreme marine temperatures can lead to the collapse of crucial marine ecosystems like coral reefs, kelp forest and seagrass meadows.
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