Is the Gulf Stream in Danger of Collapse?
Links for Friday, October 25
To the question in the title, “Is the Gulf Stream in Danger of Collapse?” the answer is yes. The only question is when — In a few decades? This century? Millennia into the future?
We commonly think of the Europe-warming Gulf Stream current as ending about the time the sun explodes; meaning “never” in practical terms. We ask, “Who will be living then?” Not one of us.
Recent studies and articles, though, say that may be false.
NOTE: I offer this information for information only; I know many of you like to keep up. I’m not offering this to induce fear. Some are already afraid, others are not. Either way, nothing any of us do will change what occurs — unless you’re a billionaire that is, a Davos man. The rest are just passengers, till they decide they’re not.
The Tipping Point for AMOC
• ‘We don’t know where the tipping point is’: climate expert on potential collapse of Atlantic circulation (Stefan Rahmstorf in The Guardian)
First, what is the AMOC? From the Guardian article (my emphasis below):
Amoc, or the Atlantic meridional overturning circulation, is a system of ocean currents that brings heat into the northern Atlantic. Warm surface water from the tropics flows north and releases its heat in the subpolar Atlantic, south of Greenland and west of Britain and Ireland. Then it cools and sinks to a depth of between 2,000m to 3,000 metres before returning south as a cold current. Amoc is one of our planet’s largest heat transport systems, moving the equivalent of 50 times the human energy use, and it has a particularly strong impact on the climate in Europe, affects the ocean’s CO2 uptake and oxygen supply, as well as rainfall patterns in the tropics.
The AMOC uses the Gulf Stream to carry heat from the tropics to northern Europe. People have known for years that it could collapse, and in the prehistorical past, has collapsed more than once.
Will our coming climate crisis cause another collapse? If so, when? The article provides a good, recent assessment by one of the most prominent scientists in this field, Stefan Rahmstorf.
First, his reason for concern:
There are indications that Amoc has been slowing down for the last 60 or 70 years due to global heating. The most ominous sign is the cold blob over the northern Atlantic. The region is the only place in the world that has cooled in the past 20 years or so, while everywhere else on the planet has warmed – a sign of reduced heat transport into that region, exactly what climate computer models have predicted in response to Amoc slowing as a result of greenhouse gas emissions.
On the timing of collapse:
The big unknown here – the billion-dollar question – is how far away this tipping point is. It is very difficult to answer because the process is non-linear and would be triggered by subtle differences in salinity, which in turn depend on amounts of rainfall and cloud cover over the ocean as well as Greenland melting rates. These are hard to model accurately in computers so there is a big uncertainty relating to when the tipping point will be reached.
The date range of estimates has narrowed:
Until a few years ago, the general thinking in the Intergovernmental Panel on Climate Change (IPCC) was that the probability of crossing the tipping point this century was less than 10%. Since then, there have been a number of studies suggesting a collapse would probably be triggered this century, possibly in the next few decades. So my risk assessment has really changed. I am now very concerned that we may push Amoc over this tipping point in the next decades. If you ask me my gut feeling, I would say the risk that we cross the tipping point this century is about 50/50. [emphasis mine]
For those studies, see “Recent AMOC Studies” below.
File under “He’s not alone.”
• Climate scientists warn Nordic ministers of changing Atlantic Ocean current (Reuters)
COPENHAGEN, Oct 21 (Reuters) - More than 40 climate scientists are urging Nordic ministers to prevent global warming from causing a major change in an Atlantic Ocean current, which could trigger abrupt shifts in weather patterns and damage ecosystems. …
Several [2021] studies have suggested that the risk of the Atlantic current changing has been greatly underestimated, the scientists said, adding that there was a serious possibility of passing the tipping point in the next few decades.
File under “Others agree.”
Recent AMOC Studies
• Probability Estimates of a 21st Century AMOC Collapse (Department of Physics, Utrecht University)
This 2024 paper is the most recent attempt to pin down tipping point timing (emphasis mine below).
Preliminary estimates of the probability of such an AMOC collapse have so far been based on conceptual models and statistical analyses of proxy data. Here, we provide observationally based estimates of such probabilities from reanalysis data. We first identify optimal observation regions of an AMOC collapse from a recent global climate model simulation. Salinity data near the southern boundary of the Atlantic turn out to be optimal to provide estimates of the time of the AMOC collapse in this model. Based on the reanalysis products, we next determine probability density functions of the AMOC collapse time.
The conclusion, from the Abstract:
The collapse time is estimated between 2037-2064 (10-90% CI [confidence interval]) with a mean of 2050 and the probability of an AMOC collapse before the year 2050 is estimated to be 59±17%.
Note: This is based on modeling and reanalysis of existing data, so it’s not quite proof. Still, something to think about; this is a serious study.
File under “What if they’re right?”
• Physics-based early warning signal shows that AMOC is on tipping course (Science)
This is one of the earlier papers the Utrecht University paper (above) refers to. The authors attempt to find a way to anticipate the AMOC collapse tipping point, in essence, find an “early warning signal.”
[W]e develop a physics-based and observable early warning signal of AMOC tipping: the minimum of the AMOC-induced freshwater transport at the southern boundary of the Atlantic. Reanalysis products indicate that the present-day AMOC is on route to tipping.
They’re among the first to identify South Atlantic salinity as an indicator.