Notably (and in alignment with the mindset of many here):
“My suspicion is that the hypothesized imminent shut down of the Atlantic Conveyor will remain somewhat controversial until, one year, we know that it is happening. It’s similar mathematically to wild gyrations of a stock market that precede a major crash. Nobody knows what is a reversible fluctuation or is a precursor to a crash. The authors say that a shutdown is imminent, and precursory instabilities are happening.
I now return you to your regularly scheduled permabear/permabull debate.
Benjamin Franklin (1706-1790) noticed something odd as Deputy Postmaster General for the American colonies in London: mail took much longer travelling west across the Atlantic than it did travelling east. Several weeks longer, in fact. In a 1746 letter, Franklin ascribes this anomaly to an effect of the Earth’s rotation, making an eastward journey faster than a westward one. By 1762, Franklin is using the term ‘Gulph Stream’ to describe the “Trade Wind blowing over the Atlantic Ocean constantly…in a strong current.” In 1768, Franklin approached his cousin, Timothy Folger, captain of a Nantucket merchant vessel who had extensive knowledge of the coastal Atlantic waters. According to Folger, Nantucket whalers had cruised their ships along the edge of the Stream while hunting for whales and were already familiar with its patterns.
The Gulf Stream is only one part of a complex pattern of currents that include the AMOC. The Gulf stream brings warm water from the south to the US east coast. The AMOC moves that water to the Arctic where it cools down and then returns to the south.
If the AMOC collapses the models show that the warm water from the Gulf Stream will build up on the US east coast, causing a one meter rise in sea levels. Reduced movement of warm water to the Arctic is projected to mean much colder water temperature around Europe, resulting in much lower temperatures on the continent. The East Coast floods, European agriculture crashes, and there are all sorts downstream impacts on the Asian monsoon pattern and Amazon forests. It gets unpredictable very fast.
The difficulty is that despite the admitted unpredictability, policy has to be made today about whether to take the issue seriously and as to how much of a sacrifice should be made now to mitigate something that only has a probability of occurring.
It’s a bit like long-term care insurance. Do you get it and make economic sacrifices today or do you take a chance and let your kids deal with it if the worse case happens.
The first thing a climate model must do is to reproduce the past.
Can we trust projections of AMOC weakening based on climate models that cannot reproduce the past?
McCarthy and Caesar https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2022.0193
“We show that both the magnitude of the trend in the AMOC over different time periods and often even the sign of the trend differs between observations and climate model ensemble mean, with the magnitude of the trend difference becoming even greater when looking at the CMIP6 ensemble compared to CMIP5.”
“We believe that progress needs to be made in understanding why models do not reproduce past AMOC variability and that this is the key to having confidence in the future evolution of this key climate variable.”
This is why the van Westen study isn’t a prediction. It explicitly states that the conditions tested were not completely realistic, for example with the amount of fresh water added. Again, what the study demonstrates is that using the most realistic model available, the addition of fresh water can collapse the AMOC. The amount of fresh water needed or the time required remain uncertain. They also identified one physical metric that indicates when an AMOC collapse is approaching. The current level of that metric suggests that we are on the pathway toward an AMOC collapse.
We all agree this isn’t conclusive. What I don’t understand is why you are trying so hard to completely dismiss it.
Not the case. I am trying to provide some perspective. Without the discussion in this thread nobody here would know that:
~ There are large annual and decadal changes in the AMOC
~ There are paleo data that indicate the AMOC has been stable since 1860 (150 years)
~ AMOC models in general do not reproduce the historical data
~ The model under discussion says nothing about where we are in the author’s scenario but there many centuries in it
~ The model uses totally unrealistic amounts of fresh water
~ The lead author of the paper says “So that is absurd and not very realistic”
Instead, people are left with headlines such as “Atlantic Ocean circulation nearing ‘devastating’ tipping point” and “AMOC current from ‘Day After Tomorrow’ is on path to collapse”.
Without some grains of salt, it is all too easy to fall into the catastrophic/apocalyptic mode (something that Steve should appreciate).
So given all these grains of salt, do you believe the study should be a concern and that steps should be taken now to reduce the probability of an AMOC collapse?
Or do you believe we should do nothing and wait until the evidence is conclusive, even if by then it is too late to do anything about it?
The house is burning down but the computer on your desk does not know it. We take time figuring out how to program the math of heat and flames. It is a mixed AI result. We get into better data mining. It is still a mixed result.
We do not call the fire department because of COVID.
There are numerous times when similar warnings of worse case scenarios caused policy changes that saved lives:
Smoking and cancer, leaded gasoline and brain damage, freon and the ozone layer, pesticides and cancer, smog and lung disease, earthquake building standards, the Clean Water Act, the Clean Air Act.
There are also times when failing to heed early warnings caused much pain and suffering. These include the Dust Bowl, thalidomide, the flooding of New Orleans by Katrina, the California wildfires.
That’s the nature of predictions, which scientists generally do not do unless forced. Scientists typically only provide probabilities of something occurring based on best available evidence. How the general public perceives that is beyond the scientists control.
The vast majority of economic predictions are wrong. But that doesn’t mean governments shouldn’t take steps to avoid economic conditions that increase the likelihood of a financial disaster. No one can predict when a recession will occur, but that doesn’t mean that a prudent investor shouldn’t take steps to prepare for such an event.
People buy insurance not because they are certain something bad will happen, only in case it does. People start eating healthy and exercise not because of the certainty of diabetes or heart attack, but to reduce the probability of the worse case scenario.
