The ice sheet and the Atlantic overturning circulation (AMOC): No Alarm

AMOC. Source: Woods Hole

By Frank Bosse

We hear it over and again: the melting ice in Greenland due to warming will soon lead to a collapse of the AMOC, making it difficult for it to “restart”.

The salt content in the north is critical because the salt-rich tropical water cools down and sinks due to the higher salt content, which is the “pump” that makes circulation possible in the first place. It also transports very large amounts of heat into the North Atlantic.

Scenarios  have been published that calculate a drastic cooling of the greater area (especially Europe) around it if the AMOC is “switched off”. The “Day after Tomorrow” scenario.

A more recent summary of these “tipping point” assumptions comes from Prof. Rahmstorf. It refers to reconstructed phases of such collapses, especially during “Heinrich Events” in the last ice age. At that time, large quantities of icebergs advanced far to the south, where they melted and thus probably brought the AMOC to a standstill through sweetening.

New paper finds no alarm

A completely new paper sheds light on these events in detail and reconstructs the freshwater inputs very precisely. A very detailed discussion can be found here.

It finds a decisive difference in the situation during the last ice age and the present: whereas at that time the ice entered the Atlantic primarily in the form of icebergs from the large continental ice sheets, in the present it is Greenland – the island supplies the lion’s share of the freshwater. This has consequences: as the glaciers continue to melt and retreat further inland, fewer and fewer icebergs are released and more and more liquid water is released. This has a major impact on the AMOC. Icebergs are much more “effective”. They briefly freeze the surrounding surface seawater, which leads to warming of the water below, as ice insulates against temperature loss to the (cold) atmosphere. Due to the large mass of the icebergs, they also travel much further south before they melt and finally disappear, leading to much larger-scale sweetening.

The paper concludes that the iceberg discharges from Greenland will not last long enough to drive the AMOC into collapse. Another reason for this is that it was much weaker in ice ages than at present anyway. The lead author of the study is quoted as saying:

This is good climate news that will hopefully dissuade people from climate doomism.”

So whoever reads something about the “soon to dry up North Atlantic Current” and the catastrophic effects in the future: The current piece in “Science” files this under doomsday fantasies (“doomism”).

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June 5, 2024 at 11:23AM

Another advance for solar-planetary theory. Some of the previous research of the HZDR group was mentioned in this Talkshop post last year. Our JEV (Jupiter-Earth-Venus) chart shown here covers 90 mean solar cycles, using the tropical orbit periods of the planets (verified on Arnholm’s solar simulator software). One point where we disagree slightly with Stefani’s HZDR group is the idea that the 193-year cycle they find is the de Vries cycle. We think not, because the de Vries cycle has a mean of 208.5~ years as Ian Wilson’s PRP paper on JEV theory explained, and other researchers have also found a similar period (say 205-210 years).
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Press release 27 May 2024: Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the University of Latvia have posited the first comprehensive physical explanation for the sun’s various activity cycles.

It identifies vortex-shaped currents on the sun, known as Rossby waves, as mediators between the tidal influences of Venus, Earth as well as Jupiter and the sun’s magnetic activity.

The researchers thus present a consistent model for solar cycles of different lengths – and another strong argument to support the previously controversial planetary hypothesis.

The results have now been published in the journal Solar Physics (DOI:10.1007/s11207-024-02295-x).

Although the sun, being near to us, is the best researched star, many questions about its physics have not yet been completely answered. These include the rhythmic fluctuations in solar activity. The most famous of these is that, on average, the sun reaches a radiation maximum every eleven years – which experts refer to as the Schwabe cycle. This cycle of activity occurs because the sun’s magnetic field changes during this period and eventually reverses polarity. This, in itself, is not unusual for a star – if it weren’t for the fact that the Schwabe cycle is remarkably stable.

The Schwabe cycle is overlaid by other, less obvious fluctuations in activity ranging from a few hundred days to several hundred years, each named after their discoverers. Although there have already been various attempts to explain these cycles and mathematical calculations, there is still no comprehensive physical model.

Planets set the beat
For some years, Dr. Frank Stefani of HZDR’s Institute of Fluid Dynamics has been an advocate of the “planetary hypothesis” because it is clear that the planets’ gravity exerts a tidal effect on the sun, similar to that of the moon on the Earth.

This effect is strongest every 11.07 years: whenever the three planets Venus, Earth and Jupiter are aligned with the sun in a particularly striking line, comparable to a spring tide on Earth when there is a new or full moon. This coincides conspicuously with the Schwabe cycle.

The sun’s magnetic field is formed by complex movements of the electrically conducting plasma inside the sun. “You can think of it like a gigantic dynamo. While this solar dynamo generates an approximately 11-year activity cycle in its own right, we think the planets’ influence then intervenes in the workings of this dynamo, repeatedly giving it a little push and thus forcing the unusually stable 11.07-year rhythm on the sun,” Stefani explains.

Several years ago, he and his colleagues discovered strong evidence of a clocked process of this kind in the available observation data. They were also able to correlate various solar cycles with the movement of the planets just using mathematical methods. At first, however, the correlation could not be sufficiently explained physically.

Rossby waves on the sun act as intermediaries
“We have now found the underlying physical mechanism. We know how much energy is required to synchronize the dynamo, and we know that this energy can be transferred to the sun by so-called Rossby waves. The great thing is that we can now not only explain the Schwabe cycle and longer solar cycles but also the shorter Rieger cycles that we hadn’t even considered previously,” says Stefani.
. . .
Does this mean the question as to whether the sun follows the planets’ beat has finally been answered? Stefani says, “We’ll probably only be 100 percent certain when we have more data. But the arguments in favor of a process clocked by the planets are now very strong.”

Full source here.

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June 5, 2024 at 10:00AM

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June 5, 2024 at 09:43AM

via Watts Up With That?

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June 5, 2024 at 09:32AM