A new study finds that the Atlantic Ocean current that brings warmth north from the tropics could collapse much sooner than scientists previously thought.
Known as the Atlantic Meridian Overturning Circulation (AMOC), this current prevents the United Kingdom and other countries in northwestern Europe from having the same icy winters that are often experienced at the same latitudes in Canada.
As warm water flows north, it cools and evaporates, becoming saltier and denser, causing it to sink and head south before being drawn to the surface and warming again, as the cycle repeats.
The greenhouse gases that people have produced since the Industrial Revolution have warmed the ocean and melted ice in the polar regions, altering the temperature and amount of fresh water in the Atlantic Ocean.
Several climate models show that Amok is likely to weaken in the future due to global warming, and the Intergovernmental Panel on Climate Change has suggested that it could lead to a collapse in the 22nd century.
For people and governments, this will fundamentally change the ability of every country to provide enough food and water for its population
Professor Penny Holiday, National Oceanographic Centre
Scientists said this would have a catastrophic effect on everyone on Earth, because within a few decades it would cause temperatures to plummet across the Northern Hemisphere and shift rainfall patterns south, starving places like the UK of fresh water needed for drinking and farming.
Another effect is that the tropics will warm faster than they currently are because heat that would normally be brought north would stay there.
The new study, published in the journal Nature Communications, indicates that a full or partial meltdown is “likely” to occur between 2025 and 2095, describing a general weakening of the current as it approaches a tipping point.
Professor Peter Detlefsen of the University of Copenhagen and lead author of the study said he was “very disturbed” by the findings but that there was still a large degree of uncertainty about when the collapse would occur and how quickly its consequences would occur.
Other scientists have questioned the accuracy of the results, saying that the study’s reliance on using sea surface temperature data as an indirect measure of changes in the Atlantic current over the past 70 years is not a reliable way to model the future.
Oceanographers have only measured AMOC directly since 2004 and many of them say it’s too early to confidently say a long-term trend.
Professor Detlevsen said the collapse in the AMOC had not occurred for at least 12,000 years, and that the only available records of what happened then are in ice core samples taken from glaciers.
These results indicate that when the AMOC collapsed, it caused the average temperature around the North Atlantic to drop by as much as 15 degrees Celsius within a decade.
Asked whether human-produced greenhouse gases were weakening AMOC, Professor Detlefsen said: “It is unlikely that we will see changes not seen in 12,000 years ago just by chance.
“We are certain that the disruption we are making over greenhouse gas emissions is the single most important cause.”
Professor Penny Holiday, Head of Marine Physics and Ocean Circulation at the National Oceanography Center in Southampton, described the collapse of the AMOC as a “high-impact, low-probability scenario” and that decades of observations were needed to pinpoint the tipping point.
She said: “For people and governments, this will fundamentally change the ability of every country to provide enough food and water for its population.
Energy supply and demand will change rapidly with new climatic conditions and infrastructures will need huge investments to adjust and adapt.
Patterns of vector-borne disease and health (including mental health) will be severely affected.
“Across the world, many terrestrial and marine ecosystems will not be able to adapt and adapt to such rapidly changing climatic conditions, and biodiversity will be severely affected.”
She said of the study: “They describe the prospect of your mom’s collapse within a few years ‘alarming’ and the evidence is something we should not ignore.
“It’s hard to disagree with that.”