This is the confidence of one paper from one analysis technique. They might be right, or maybe not. Stefan Rahmstorf has a summary at realclimate.org and concludes:
Timing of the critical AMOC transition is still highly uncertain, but increasingly the evidence points to the risk being far greater than 10 % during this century – even rather worrying for the next few decades. The conservative IPCC estimate, based on climate models which are too stable and don’t get the full freshwater forcing, is in my view outdated now.
Deja vu all over again. We did this thread topic just two weeks ago. Where is our institutional memory?
From the CNN article on the paper:
“Scientists uninvolved with this study told CNN the exact tipping point for the critical system is uncertain, and that measurements of the currents have so far showed little trend or change. ”
And speaking of little trend, Fraser and Cunningham reconstructed the AMOC (Atlantic Meridional Overturning Circulation) back to 1900. Looking at their Figure 3, it can be seen that the current strength is now where it was in 1910 and stronger than it was in 1900 and 1970.
So, no resolution on the condition of the AMOC. Certainly not ‘settled science’. The current has large interdecadal variability.
Jackson et al. found that “the observed decrease in the overturning circulation is consistent with a recovery following a previous increase.” https://www.nature.com/articles/ngeo2715
DB2
In the distant past, the AMOC crossed the tipping point, causing large climate changes.
Predicting the exact location of tipping points, in climate and pretty much every field of science, is very hard and is the subject of intense research.
Human caused climate change is pushing us closer to the tipping point, but we don’t know how far away we still are.
Large, rapid changes in the AMOC are a serious risk but not a certainty.
In the words of the famous philosopher, Harry Callahan,
IIRC, that was due to the sudden emptying of an enormous glacial lake in Canada, Lake Agassiz, larger than the Black Sea. I don’t see anything like that at present.
According to Wikipedia, the Black Sea has 547,000 cubic km of water. The Greenland ice sheet has about 3,000,000 cubic km of ice. That’s about 8% of the global supply of fresh water.
Heinrich event ice discharge and the fate of the Atlantic Meridional Overturning Circulation
Zhou and McManus https://www.science.org/doi/10.1126/science.adh8369
Editor’s summary:
Will ice mass loss from the Greenland Ice Sheet caused by climate warming disrupt large-scale ocean circulation? Zhou et al. reconstructed iceberg production rates during the massive calving episodes of the last glacial period, called Heinrich events, when icebergs did affect ocean circulation. The authors found that present-day Greenland Ice Sheet calving rates are as high as during some of those events.
However, because melting is causing the Greenland Ice Sheet to recede from the coasts of Greenland, where icebergs originate, its iceberg discharge should not persist long enough to cause major disruption of the Atlantic overturning circulation by itself.
DB, you are selective or you do not do the basic work involved.
During Heinrich events, great armadas of icebergs episodically flooded the North Atlantic Ocean and weakened overturning circulation. The ice discharges of these episodes constrain the sensitivity of overturning circulation to iceberg melting. We reconstructed these ice discharges to be as high as 0.13 sverdrup (Sv) (1 Sv = 1 million cubic meters per second) during Heinrich event 4 and to average 0.029 Sv over all episodes. The present-day Greenland Ice Sheet calving of icebergs is comparable to that of a mid-range Heinrich event. As the future Greenland Ice Sheet recedes from marine-terminating outlets, its iceberg calving likely will not persist long enough for icebergs alone to cause catastrophic disruption to the Atlantic overturning circulation, although the accelerating Greenland runoff and continued global warming remain threats to the circulation stability.
“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.”
This is indeed good news. However, the authors caution that ice sheet melting will still continue on land. The authors’ abstract, their summary, says this
the accelerating Greenland runoff and continued global warming remain threats to the circulation stability.
It’s curious that the editors left this part out of their summary.
AMOC is driven by dense sinking water near Greenland and Antarctica. The water is dense because it’s cold and relatively fresh. Glacial runoff and melting icebergs both add fresh water to the sea and they have different impacts on AMOC.
The authors close their article with
Although surface melting–induced runoff is less effective at disrupting the AMOC than ice discharge, it cannot be entirely ignored. Runoff is projected to increase and overtake ice discharge as the leading cause of GrIS (Greenland Ice Sheet) mass loss by 2100 Therefore, the future trajectory of the AMOC strength will likely be determined by a “tug of war” in influence between the decelerating but more effective ice discharge and the accelerating but less influential runoff. Compounded with continued warming and the resultant increase in surface water buoyancy, the fate of the AMOC remains precariously unclear.
FWIW, Greenland seems to have gone through a warm period lasting over five centuries without the AMOC going through some irreversible tipping point.
Strunk et al. studied organic debris in west Greenland to reconstruct the climate. They write that “We identify three distinct periods of climate regimes: From c. 560–1100 CE conditions were stable, warm and humid, and summer temperatures were 1.5–2°C warmer than today.”
