One of the great – and most significant current scientific puzzles – is what’s happening with the Atlantic meridional overturning circulation (AMOC) and the decline of the Antarctic Circumpolar Current.

For some time there have been indications that AMOC may reverse itself with wide ranging impacts – for instance bringing a new Ice Age to the Northern hemisphere or at least other less dramatic impacts more widely.

Recently there has been a number of research papers discussing the complexity of the situation. Dr. Jonathan Baker, a scientist at the Met Office and the lead author of a Nature paper on AMOC said: “The AMOC has a crucial role in regulating our climate; without it, northwest Europe’s temperatures would be much cooler. Our modelling study suggests that the AMOC will resist pressures from rising global temperatures and inputs of freshwater into the North Atlantic, with the weakened system being largely driven by winds over the Southern Ocean. Although our study shows that collapse over the next 75 years is unlikely, the AMOC is very likely to weaken, which will present climate challenges for Europe and beyond.”

Professor Rowan Sutton, Director of the Met Office Hadley Center, said, “This study brings important new insights into the future of the AMOC. It shows that aspects of the AMOC may be more robust to a changing climate than some previous research has suggested. For some years there have been indications that AMOC is becoming unstable but that predicting when it might collapse is a more complex problem.”

Professor Andrew Watson, from the University of Exeter, added, “What we are finding is that, so long as the winds blow around the Southern Ocean, water is drawn up from the deep ocean there. That water has to be balanced by sinking water somewhere, and that somewhere tends to be the North Atlantic. So the AMOC is not only controlled by the local conditions, but also what’s happening at the other end of the Earth.”

And there’s the rub with AMOC predictions – what’s happening at the other end of the world.

A paper by a number of Australian, Indian and Norwegian authors in the Environmental Research Letters (3/3) looks at the Antarctic Circumpolar Current and suggests that it is declining due to polar ocean freshening.

The author’s say “The Southern Ocean is in a state of rapid change. Satellite observations reveal that the Antarctic ice sheet is losing mass at an accelerating rate, releasing large amounts of freshwater into the ocean along the Antarctic coast. Sea ice extent, which was slightly increasing until 2016 has since rapidly declined,” they say.

The paper’s Abstract gives more detail: “The Antarctic Circumpolar Current (ACC) is the world’s strongest ocean current and plays a disproportionate role in the climate system due to its role as a conduit for major ocean basins. This current system is linked to the ocean’s vertical overturning circulation, and is thus pivotal to the uptake of heat and CO₂ in the ocean. The strength of the ACC has varied substantially across warm and cold climates in Earth’s past, but the exact dynamical drivers of this change remain elusive.

“This is in part because ocean models have historically been unable to adequately resolve the small-scale processes that control current strength. Here, we assess a global ocean model simulation which resolves such processes to diagnose the impact of changing thermal, haline and wind conditions on the strength of the ACC.

“Our results show that, by 2050, the strength of the ACC declines by ∼20% for a high-emissions scenario. “This decline is driven by meltwater from ice shelves around Antarctica, which is exported to lower latitudes via the Antarctic Intermediate Water.

“This process weakens the zonal density stratification historically supported by surface temperature gradients, resulting in a slowdown of sub-surface zonal currents. Such a decline in transport, if realised, would have major implications on the global ocean circulation.”

Meanwhile, the climate catastrophe which Peter Dutton and Donald Trump are denying, is of rather more concern to the Allianz SE, one of the world’s biggest insurance companies. Gunther Thallinger, formerly Chair of the company’s investment company and CEO I Allianz Investment Management, has posted a Linked in Post (25/3), which argues that “the world is fast approaching temperature levels where insurers will no longer be able to offer cover for many climate risks.”

He predicted that: “These extreme weather phenomena drive direct physical risks to all categories of human-owned assets—land, houses, roads, power lines, railways, ports, and factories. Heat and water destroy capital. Flooded homes lose value. Overheated cities become uninhabitable. Entire asset classes are degrading in real time, which translates to loss of value, business interruption, and market devaluation on a systemic level.

“The insurance industry has historically managed these risks. But we are fast approaching temperature levels—1.5°C, 2°C, 3°C—where insurers will no longer be able to offer coverage for many of these risks. The math breaks down: the premiums required exceed what people or companies can pay. This is already happening. Entire regions are becoming uninsurable. (See: State Farm and Allstate exiting California’s home insurance market due to wildfire risk, 2023).

“This is not a one-off market adjustment. This is a systemic risk that threatens the very foundation of the financial sector. If insurance is no longer available, other financial services become unavailable too. A house that cannot be insured cannot be mortgaged. No bank will issue loans for uninsurable property. Credit markets freeze. This is a climate-induced credit crunch.

“This applies not only to housing, but to infrastructure, transportation, agriculture, and industry. The economic value of entire regions—coastal, arid, wildfire-prone—will begin to vanish from financial ledgers. Markets will reprice, rapidly and brutally. This is what a climate-driven market failure looks like.”

Communists never managed to bring the capitalist system down but obviously the capitalist system itself may do the job in their place. No vanguard revolutionary party will be needed.

But Thallinger does provide some good news “We already have the technologies to switch from fossil combustion to zero-emission energy. Solar, wind, battery storage, green hydrogen, electrification, grid modernisation, demand side efficiency – these are mature and scalable solutions. “

That message hasn’t got to Peter Dutton and Trump but it has to the insurance and finance industries. Of course, Dutton says there is a scientific answer – nuclear power.  As my friend, John Spitzer, said recently: “When Dutton said he could not comment on climate change because he was not a scientist, one wonders how he arrived at his nuclear energy policy.”

John Spitzer also alerted the blog to the Environmental Research Letters paper.