A dramatic increase of carbon dioxide levels in the Earth's atmosphere could lead to the collapse of a large Atlantic Ocean current that was previously thought to be able to withstand such changes, a new study suggests.
Past climate models have predicted that the Atlantic Meridional Overturning Current (AMOC) is a stable ocean current that would remain intact even after centuries of atmospheric concentrations of carbon dioxide double from 1990 levels.
The new study published in the journal Science Advances suggests that AMOC is, in fact, more sensitive and would collapse after 300 years of doubled atmospheric carbon dioxide.
Existing climate models were subject to biases that made them treat AMOC as particularly stable, according to researchers at the University of California, San Diego and the University of Wisconsin-Madison in the US.
In the new model, scientists factored in how fresh water was also being circulated by AMOC between the Atlantic and the Arctic and corrected for biases in the existing climate models. They found that fresh water is likely to accumulate in the North Atlantic, which would amplify the collapse in the AMOC.
"Compared with an uncorrected model, the AMOC collapse brings about large, markedly different climate responses: a prominent cooling over the northern North Atlantic and neighbouring areas, sea ice increases over the Greenland-Iceland-Norwegian seas and to the south of Greenland, and a significant southward rain-belt migration over the tropical Atlantic," the authors write in the paper.
What does AMOC do?
If AMOC shut down entirely, it would be likely to have profound effects on the global climate. AMOC carries heat north from the equatorial regions towards the North Pole, having a strong effect on the weather of countries in Europe in particular.
"I think it is very robust to build the link between the AMOC and colder winters in the Atlantic rim countries," study author Wei Liu of the University of California, San Diego, told IBTimes UK.
"The AMOC carries huge oceanic heat northward and contributes to the moderate climate of the UK and north-west Europe. A severe weakening or collapse of the circulation will halt this heat transport and definitely bring about great cooling and colder winters in these areas."
Low AMOC activity in 2009-10 and 2010-11 is thought to have been behind particularly cold winters in Europe in those years. There is already evidence that the AMOC has destabilised since the early 20th century, and a downturn in AMOC has also been linked to significant sea-level rise.
The shutdown of ocean currents such as AMOC is the premise for the apocalyptic film The Day After Tomorrow, where a collapse of AMOC leads to an abrupt ice age. Recent research predicting what would happen if AMOC did collapse suggests that temperatures would indeed cool, but only temporarily and nowhere near so dramatically as the Hollywood film imagines.