Increasingly more scientists have recently argued that multiple, dangerous tipping points are most likely approaching worldwide due to anthropogenic climate change. Now, a team of experts from the University of Exeter has used centuries-old clam shells to investigate how the North Atlantic climate system reached such a tipping point before the Little Ice Age – a period of regional cooling (most pronounced in the North Atlantic region) that occurred between the 14th and 19th centuries.
A long-standing scientific theory suggests that the initial cooling in this period was sustained by so-called “sea-ice to ocean feedbacks” – a phenomenon in which sea-ice expansion slowed ocean currents, which in turn significantly reduced the flow of warm water from the South.
By analyzing shells of quahog clams – which can live for several centuries – the researchers aimed to understand how the ocean has evolved and responded to external changes during the past centuries. The experts discovered that the North Atlantic climate system destabilized and lost resilience immediately before the Little Ice Age, possibly causing the Earth to tip into a new, colder state.
“One way to tell that a system is approaching a sudden transition is that it becomes slow to respond to perturbations (external changes),” said study lead author Beatriz Arellano-Nava, a doctoral student in Geography and Global Systems at the University of Exeter. “In other words, a system loses the ability to return to its average state, and can instead ‘tip’ into a new state.”
“In the case of the North Atlantic prior to the Little Ice Age, this loss of resilience made the system vulnerable to an abrupt switch, potentially heralding the transition to Little Ice Age conditions,” added study co-author Paul Halloran, an associate professor of Earth Sciences at the same university.
According to the scientists, the North Atlantic could be approaching once more a tipping point, with major consequences for the world’s climate.
“Our latest analysis suggests that the system of ocean currents in the northern North Atlantic could be at risk of a tipping point again now due to global warming, leading once again to abrupt climate change over Europe,” concluded study senior author Timothy Lenton, the director of Exeter’s Global Systems Institute.
The study is published in the journal Nature Communications.