The potential collapse of the Atlantic Ocean currents, which could lead to drastic weather changes and potentially cause Europe to experience an intense cold spell, appears improbable this century, according to a recent study.
In prior years, research has fueled concerns about the deceleration and possible abrupt halt of the Atlantic segment of the ocean’s conveyor belt system, a crucial element in global weather dynamics due to its role in transporting warm water northward and cool water south. Scientists warn that a climate change-induced shutdown of the Atlantic Meridional Overturning Circulation (AMOC) could disrupt global precipitation patterns, significantly chill Europe while warming other parts of the planet, and increase sea levels along America’s East Coast.
The concept of these catastrophic changes was popularized in the 2004 fictional disaster film “The Day After Tomorrow,” depicting climate change triggering enormous storms, widespread flooding, and a new ice age.
Researchers from the UK’s Met Office and the University of Exeter tested 34 different computer models simulating extreme climate change scenarios to evaluate the likelihood of AMOC collapsing within this century. As published in Wednesday’s issue of the journal Nature, their findings suggest that a total shutdown is unlikely before the year 2100, stated Jonathan Baker, the study’s lead author and an oceanographer at the Met Office.
Even though such a collapse could happen beyond 2100, Baker emphasized that the currents have failed in the distant past. Nonetheless, these computer model simulations are “reassuring,” according to Baker.
“However, this should not breed complacency,” Baker added. “The AMOC is expected to weaken significantly this century, posing major climatic impacts of its own.”
The Atlantic current functions as warm water cools upon reaching the Arctic, forming sea ice and leaving salt behind, which increases water density, prompting it to sink and move southwards. Yet, as climate change continues to increase global temperatures and as more fresh water from the melting Greenland ice sheet enters the Arctic, the Arctic mechanism that fuels the ocean conveyor tends to slow down. Earlier studies even predicted a full stop, with some suggesting it might occur within decades.
Baker argues, however, that the computer models and fundamental physics indicate a secondary motor effect around the Southern Ocean encircling Antarctica. Here, winds cause upwelling, where water resurfaces and warms. While this is not as strong, it is expected to sustain the current system, albeit weakened, until at least the end of the century, he explained.
Focusing on the ascent of water from deeper ocean levels, rather than solely on its descent, Baker’s approach provides fresh insights and challenges studies foretelling imminent collapse, said Andreas Schmittner, a climate scientist from Oregon State University, not involved in this research.
According to Baker, winds over the Southern Ocean that draw water from the depths act “like a powerful pump that keeps the AMOC operational even under extreme climate changes.”
The computer models predicted that as the AMOC weakens, a weaker Pacific version will likely develop to counterbalance any loss.
If the AMOC weakens without complete collapse, many impacts such as agricultural disruptions and fish population shifts would likely still occur, though not the extreme scenario of Europe plunging into a major freeze, Baker warned.
Scientists use the unit Sverdrups to measure AMOC strength. Currently, AMOC measures around 17 Sverdrups, a decrease of two since 2004, with a decline trend of approximately 0.8 per decade, experts noted.
Debate exists in scientific circles regarding what constitutes an AMOC shutdown. While Baker defines it as 0 Sverdrups, other researchers indicating shutdown implications use about 5 Sverdrups. Though three of Baker’s 34 models reached below 5 Sverdrups, none reached zero.
Thus, Levke Caesar and Stefan Rahmstorf, physicists at the Potsdam Institute for Climate Research involved in an alarming 2018 study on shutdown prospects, indicated their work aligns with this new study’s findings, as it largely pertains to definitional nuance.
“An AMOC collapse doesn’t require 0 Sverdrups overturning; defining it as such implies that significant AMOC weakening already entails numerous consequences,” stated Caesar through an email. “The models demonstrate considerable weakening that harbors serious repercussions.”
