There have long been worries that a critical network of currents in the Atlantic Ocean could come to a halt catastrophically as the climate changes. Credit: Gordon Scammell/Loop Images/Universal Images Group/Getty
A crucial ocean-current system seems unlikely to collapse even in the face of severe climate change ― despite predictions that it would disintegrate if Earth continues to warm. That’s the finding of a study1 suggesting that the Atlantic Meridional Overturning Circulation (AMOC) will survive at least until the end of the century.
The study found that the combined forces of various ocean currents and winds would keep the system stable even under the most pessimistic climate scenarios.
The authors are confident that there is sufficient evidence to support this finding, even though the climate models they analysed do not perfectly mirror reality. “Unlikely isn’t impossible,” says Jonathan Baker, a co-author of the study and a climate scientist at the Met Office in Exeter, UK. “But we have confidence in our results.” The work is published today in Nature.
Water-moving machine
The AMOC is like a giant conveyor belt in the Atlantic Ocean: warm water travels in the upper layers from south to north. Once the water reaches its northernmost point, it sinks and travels southwards in a cold, deep layer until it reaches the southern oceans, where it rises back up to the surface. The AMOC therefore has a crucial role in the global distribution of heat, salt and other components of seawater.
The system called the Atlantic Meridional Overturning Circulation (warm water in red, cold water in blue; artist’s illustration) would survive, although in weakened form, even with extreme climate change.Credit: Jonathan Baker (Met Office) and co-authors
The intensity of the AMOC has declined over time2, a trend traced to polar ice melt, changes in wind patterns and precipitation changes linked to climate change. Although scientists agree that the collapse of the AMOC would have devastating consequences for local and regional climates, they are divided on whether and when such an event would occur.
Studies of the AMOC’s future generally rely on analyses of its past behaviour and on models that simulate future scenarios under different climate conditions. Some have concluded that the AMOC would reach a tipping point sometime between 2025 and 2095, then abruptly shut down3. Other research indicates that a collapse is unlikely before the end of the century2, but scientists had not previously identified the factors that might be stopping it from happening.
A passel of models
Baker and his team used 34 climate models to examine how the AMOC might respond to two extreme scenarios: a four-fold increase in carbon-dioxide levels from pre-industrial levels; and the addition of massive amounts of freshwater, consistent with the melting of the Greenland ice sheet. The team found that the AMOC would weaken in both scenarios, but not collapse.
