Typically excellent PBS production describes important new research on the Atlantic Meriodonal Overturning Circulation (AMOC), which readers of these pages will know is the critical global circulation that is being destabilized by steady climate warming.
The worry has been that if warming reaches a certain temperature range, the current will collapse and bring chaotic sudden change to weather systems around the planet. New research suggests it’s not the temperature, so much as the speed of warming. Lead investigator interviewed here.
His message: it’s what we do now that counts.
Nature – Failure to Track a Stable AMOC State under Rapid Climate Warming:
The Atlantic Meridional Overturning Circulation (AMOC), a tipping element of the climate system, currently has an estimated global warming threshold for collapse of +4.0 °C (uncertainty range 1.4–8 °C). However, such a threshold may not be meaningful because AMOC stability depends on the rate of radiative forcing change, not a set temperature. Here we identify an AMOC stabilizing mechanism that operates on timescales slower than present-day warming rates. Slow forcing permits coherent adjustment of surface and interior ocean properties, supported by enhanced evaporation and reduced sea-ice extent, counteracting destabilizing feedbacks. Using a slow CO2 ramp (+0.5 ppm yr−1) climate model simulation, we explicitly demonstrate the AMOC remains stable up to +5.5 °C of global warming. By contrast, under faster CO2 ramps, the AMOC collapses at substantially lower warming levels (+2 °C). Our findings demonstrate rate-induced AMOC tipping and imply that limiting the rate of emissions is critical for reducing the risk of an AMOC collapse.