- by Tom Housden
- BBC News, Sydney
A new report warns that the rapid melting of Antarctic ice is causing a significant slowdown in deep ocean currents and could have disastrous effects on the climate.
A team of Australian scientists say the deep-water flows that drive ocean currents could decline by up to 40% by 2050.
Currents carry vital heat, oxygen, carbon and nutrients around the world.
Previous studies have suggested that the slowing of the North Atlantic Current may be causing Europe to cool.
The study, published in the journal Nature, also warns that a slowdown could reduce the ability of the oceans to absorb carbon dioxide from the atmosphere.
The report shows how Earth’s network of deep ocean currents is driven in part by the downward movement of cold, dense, salty water toward the ocean floor near Antarctica.
But as the fresh water from the permafrost melts, the seawater becomes less salty and denser, and the downward motion slows.
Scientists say deep ocean currents, or “fluctuations,” in the northern and southern hemispheres have been relatively stable for thousands of years, but are now disrupted by a warming climate.
“Our models suggest that if global carbon emissions continue at current rates, Antarctic reversals will slow by more than 40 percent in the next 30 years – and on a trajectory that appears to be headed for collapse,” said Professor Matthew England, lead study author of the study. .
“If the ocean had lungs, it would,” Professor England, an oceanographer at the University of New South Wales, Sydney, told a news conference.
Reduced ocean circulation means the carbon-absorbing waters on the surface are quickly reaching capacity, said Dr. Adele Morrison, who contributed to the study, and is not replaced by carbon-unsaturated water from deeper depths.
A 2018 Atlas study found that the Atlantic circulation system is weaker than it has been in more than 1,000 years, and has changed dramatically in the last 150 years.
This suggests that changes in the Atlantic reverse circulation (Amoc) such as the conveyor belt could cool the oceans and northwestern Europe, and affect deep-sea ecosystems.
Amok’s dramatic portrayal of closing was featured in the 2004 climate disaster film The Day After Tomorrow.
But Dr Morrison said a slowdown to the south of the reverse would have an even bigger impact on marine ecosystems and Antarctica itself.
“Turnover brings nutrients that sink to the bottom when organisms die… to supply ecosystems and global fisheries,” he told the BBC.
“Another bigger effect it could have is feedback on how much Antarctica will melt in the future. And as that rise slows, it opens a pathway for warmer water which can cause increased melting, which will act as an additional feedback, causing more water to melt in the oceans and slowing that circulation even further.”
The scientists spent 35 million computing hours over two years producing their model, which shows that deep water circulation in Antarctica could slow the North Atlantic’s doubling rate of sinking.
“[It’s] It’s amazing to see this happen so quickly, said climate scientist Alan Meeks of Oregon State University, co-author of the most recent IPCC assessment.
“Looks like he’s on the move now. This is big news,” he told Reuters.
Britain says the impact of Antarctic melting waters on ocean currents is not yet accounted for in the IPCC climate change models, but will be “significant”.
