The future of the Atlantic circulation will be determined by a tug-o-war between Greenland's decreasing ice flux and its increasing freshwater runoff.
Zhou compared the rate of icebergs coming from the Greenland Ice Sheet to ice flux during Heinrich Events, the last time the AMOC collapsed. He found that as Greenland's ice sheet retreats inland, its iceberg calving likely will not persist long enough to completely derail the Atlantic circulation. That said, increased freshwater runoff and continued global warming remain threats to the circulation's stability.
Zhou went back in history to study the most recent period when the AMOC was severely weakened -- from 68,000 to 16,000 years ago, during the last glacial period. During cooler periods there is more water locked up in ice sheets, creating a reservoir for quickly flushing the ocean with freshwater in the form of icebergs or runoff. Scientists call these episodes Heinrich Events when they came from the Laurentide Ice Sheet."Today it does not exist.
Heinrich Events also lasted for tens to hundreds of years. In contrast, the industrial revolution only began around the late 18century, with carbon emissions ramping up much later."It is possible that we simply haven't screwed up badly enough for long enough for it to really mess up the AMOC," Zhou remarked.
"This presents a tug-o-war between these two factors: the more disruptive but decreasing ice discharge and the less effective but accelerating runoff," Zhou explained."It's going to be a competition, and the interplay between the two will determine the future of the AMOC." "We have a lot of anxiety about how fast climate change is happening and how dramatic the changes could be," Zhou said."But this is a piece of good climate news that hopefully will dissuade people from climate doomism, and give people hope, because we do need hope to fight the climate crisis."Climate change is driving increasing amounts of freshwater into the Arctic Ocean.