A new study by Wei Lui, a Yale University researcher, reveals that the ongoing process of climate change could trigger catastrophic collapse of a vital Atlantic Ocean current mechanism known as the Atlantic Meridional Overturning Circulation (AMOC). AMOC is a natural process that helps to maintain global climate and weather conditions within limits conducive for the sustenance of life by distributing heat from the tropics to the North Atlantic region that includes northern Europe and North America.
According to Wei Lui, researcher from the Department of Geology and Geophysics at Yale University, and lead author of the new study published in the journal Science Advances, AMOC brings warmth to the North Atlantic region by transporting warmer water from the tropics to the cooler North Atlantic region. When the warm water reaches the Northern Hemisphere it loses heat to the environment. The denser, cooled water then sinks and flows back to tropics where it is warmed again to repeat the process, according to a release by Yale University.
Because AMOC plays a vital role in contributing heat needed to sustain current climactic and weather conditions in the North Atlantic region, collapse could plunge large parts of the Northern Hemisphere, especially North Atlantic countries, into extreme winter conditions that transform the entire region into frigid wastelands.
“We show that the possibility of a collapsed AMOC under global warming is hugely underestimated.”
According to the new study, AMOC could collapse due to warming of air in the Northern Hemisphere as part of ongoing climate change. When air temperatures in the Northern Hemisphere reach a critical point, AMOC will not be able to unload warmth from warm waters into the air. This will lead to a permanent shutdown of the mechanism that sustains the heat distributing circulation of Atlantic Ocean currents.
What follows, according to Liu and study colleagues, is a catastrophic doomsday scenario where the ripple effect from the breakdown of AMOC in the Northern Hemisphere is felt globally as the collapse of the essential self-regulatory mechanisms of global climate.
“It [AMOC] is a major player in the climate system, important for Europe and North America. So it’s a big deal,” Tom Delworth, a climate expert at the National Oceanic and Atmospheric Administration, said, according to The Verge.
The plot of the 2004 sci-fi movie The Day After Tomorrow was inspired by debate among experts about the possible impact of ongoing climate change on AMOC.
In his new study, Liu and his colleagues calculated that carbon dioxide concentration in the atmosphere would need to reach 710 parts per million (ppm) for the collapse to occur. The current level, according to latest measurements, is 405 ppm, compared with 355 ppm in 1990.
The researchers calculated that at the present rate of build-up of atmospheric carbon dioxide due to human industrial activity, the collapse of AMOC could take up to 300 years to occur. But once the collapse occurs it could transform North America and Europe into frigid wastelands very rapidly.
Liu and his colleagues also warned that their mathematical model suggests that AMOC is already weakening and showing signs of slowing down. Eventual collapse could trigger catastrophic “prominent cooling “of the North Atlantic region, leading to a “remarkable sea ice expansion.”
“[Our model] predicts a future AMOC collapse with prominent cooling over the northern North Atlantic. This has enormous implications for global climate change.”
Scientists believe there is evidence from the paleoclimatic records that melting ice sheets once caused AMOC to cease for decades, triggering dramatic changes in hurricane and monsoon rainfall patterns in Africa and India. It is also believed to have triggered a mini ice age in the Northern Hemisphere.
The effect of shutdown of AMOC will not be limited to the northern parts of the world. Shutdown of cold water flows from the north to the south could push the current rain belt of the temperate region southward into the tropical Atlantic and intensify warming in the equator. This will lead to increases in rainfall in areas such as north-eastern Brazil, while Central America experiences inadequate rainfall.
It could also lead to a dramatic reduction in Antarctica sea ice, the study concluded.
Liu emphasized the vital life-sustaining role of AMOC, saying that shutdown of the vital Atlantic current could have catastrophic consequences for human populations. He noted that it took so long to elucidate the potential impact of increasing atmospheric carbon dioxide levels that could lead to a shutdown of AMOC because previous climate change models overestimated its stability due to failure to reflect accurately the contribution of freshwater to the Atlantic current.
“The significance of our study is to point out a systematic bias in current climate models that hinders a correct climate projection.”
Several studies actually suggested that ongoing climate change would not affect AMOC. Others concluded that it could weaken it but that it would persist as global temperatures rise.
“So it’s about how well models represent the movement of freshwater out of the Atlantic,” Delworth said, according to The Verge.
Liu’s mathematical model of the impact of rising atmospheric carbon dioxide on AMOC suggests that Iceland could see a temperature drop by as much as 10 degrees Celsius in winter, while Britain could see a drop by as much as three degrees Celsius.
Co-author of the study, Zhengyu Liu of the University of Wisconsin-Madison, said that the study presents a “ground-breaking idea” that radically changed his way of thinking about the climate change process.
“For me, it’s a 180-degree turn because I had been thinking like everyone else,” he said.
[Featured image by Robert Cicchetti/Shutterstock]