A major system of ocean currents in the Atlantic could be on the verge of collapse as early as 2025, according to new peer-reviewed research.
“Here we calculate when the warning signs are significantly higher than the natural variations,” to write physicist Peter Ditlevsen and statistician Susanne Ditlevsen from the University of Copenhagen.
“Given the importance of the AMOC to the climate system, we should not ignore such clear indicators of impending collapse.”
THE Meridional Overturning Circulation of the Atlantic (AMOC) is a large system of ocean currents that includes the well-known Gulf Stream and regulates ocean heat transfer from the tropics to the northern hemisphere.
As such, it impacts much of Earth’s climate. It is considered one of the most important tipping elements in the Earth’s climate system and has slowed since the mid 1900s.
If it stalls completely, monsoon seasons will likely be disrupted in the tropics, and Europe and North America will experience dangerously harsher winters. The ripple effects will have serious repercussions on entire ecosystems and our food security.
The AMOC has only been tracked directly since 2004, which is not long enough to understand the full trajectory of its current downtrend.
So, by examining many models, the researchers identified an ocean area where sea surface temperatures most closely match ocean circulation conditions, to be used as one of two less direct indicators for which records have existed since 1870.
The other early warning sign the researchers consider is the “loss of resilience” of the system, which results in increased fluctuations and variance, like the increasing oscillation of a spinning top before it topples over.
Using these two warning signs to assess AMOC status is a bit like measuring pulse and blood pressure to monitor heart health.
The team’s modeling suggests that this all-important ocean circulation could end as early as 2025, and likely no later than 2095.
These results are alarming earlier than the most recent IPCC predictions, but early warning signs are already clear, say Peter Ditlevsen and Susanne Ditlevsen.
Previous models have “biases toward overestimated AMOC stability, both from listening to the historic climatic recordpoor representation of deep water formationsalinity and glacial runoff“, underlines the team in the newspaper.
Moreover, the speed at which we reach this destabilizing event could also determine whether the system collapses or stabilizes.
Since we have not only failed to reduce the amount of greenhouse gases we have released into the atmosphere so far, but increased them instead – it is certain looks like we’re on a scary path to reach this powerful and fast oceanic threshold.
Previous research has also shown that changing a single parameter, such as increasing the amount of fresh water entering the North Atlantic, can lead to a bifurcated – lead to a sudden and drastic change in the behavior of the system.
This level of sensitivity may not have been maintained in the IPCC assessment, as not all of the models they included take it into consideration.
We still don’t understand all of the factors that could impact this system, and other researchers have suggested things like the impact of cold water influx do not fully match past climate records.
Researchers believe their method of focusing on early warning symptoms avoids having to fully understand these factors, but beware, they can’t rule out some unknown unknowns create a different result. They also cannot distinguish between a partial or the complete collapse of the AMOC, they explain.
“Even with these caveats, this is indeed a worrying result, which should call for prompt and effective action to reduce global greenhouse gas emissions to avoid the constant shift in the control parameter towards AMOC collapse,” the team said. concludes.
This research was published in Nature Communication.