The complete collapse of an Atlantic current vital to climatic stability and nutrient-rich oceans is unlikely this century, finds a new study. But that’s no cause for complacency, its authors warn.
Essential to moderating Europe’s climate, keeping the possibility of crop-sustaining rains alive for India, South America, and West Africa, circulating vital nutrients through the water column, and storing carbon at depth, the Atlantic Meridional Overturning Circulation (AMOC) is “unlikely” to collapse completely before 2100, say the authors of a study just published in the journal Nature. It is, however, “projected to weaken owing to global warming, with significant global climate impacts.”
Existing courtesy of what is known as the thermohaline incline, a measure of water salinity and temperature, the AMOC has been turning over for millennia with warm, salty water from the tropics moving north to Greenland, where it cools and sinks, picking up nutrients as it goes, before shuttling south once more.
With freshwater from the melting Greenland ice sheet now seriously disrupting the thermohaline incline, some feared the current might collapse this century.
Running scenarios across 34 different climate models, climate scientists at the United Kingdom’s Met Office and the University of Exeter found that in all cases, the AMOC remains resilient to “extreme greenhouse gas and North Atlantic freshwater forcings.”
Such resilience owes to persistent winds out of the Southern Ocean (which encircles Antarctica) that drive upwellings there. This Southern Ocean upwelling (SO) is what will keep the AMOC alive, at least through 2100.
The authors caution that further study is urgently needed to understand how the AMOC interacts with the SO, and the potential development of a “compensating Pacific Meridional Overturning Circulation (PMOC)”—with the latter posing a particular risk to its Atlantic counterpart.
While findings about the relative stability of the AMOC may seem “reassuring,” policymakers must not treat them as a licence to back off on emissions cuts, Jonathan Baker, lead author and UK Met Office oceanographer, told the Associated Press.
“This is no green light for complacency,” Baker warned. “The AMOC is very likely to weaken this century and that brings its own major climate impacts.”
Significant threats to food security, from crop losses due to drought and changes in fish stocks as ocean nutrient caches shift or disappear, will be among those impacts, the oceanographer warns.
