Thermohaline watch

[raspberry-blower]

Guardian: Research finds the Gulf Stream at the weakest for 1600 years

The warm Atlantic current linked to severe and abrupt changes in the climate in the past is now at its weakest in at least 1,600 years, new research shows. The findings, based on multiple lines of scientific evidence, throw into question previous predictions that a catastrophic collapse of the Gulf Stream would take centuries to occur.

Such a collapse would see western Europe suffer far more extreme winters, sea levels rise fast on the eastern seaboard of the US and would disrupt vital tropical rains. The new research shows the current is now 15% weaker than around 400AD, an exceptionally large deviation, and that human-caused global warming is responsible for at least a significant part of the weakening.

A thread dedicated to the oceanic heat transportation system and what its potential consequences of it slowing up - which it appears to be doing

[emordnilap]

Can anyone explain for me how a slowing down of AMOC raises sea levels? Serious question.

[kenneal - lagger]

The slowing of the rate of flow means that the water level rises. Fact of fluid dynamics.

[RenewableCandy]

Leaving aside the cooling effect this is going to have on the UK (we're about the same latitude, here in York, as Moscow is), we'll also be a LOT drier because we'll have a cold sea upwind of us. Other places with a cold sea upwind include the Namib desert and California - home of Death Valley & a load of forest fires.

We'll have to resort to using fog-catchers to collect water.

<looks out of window at interminable rain>
<sighs>

[emordnilap]

The slowing of the rate of flow means that the water level rises. Fact of fluid dynamics.

Thanks. Interesting.

[woodburner]

The slowing of the rate of flow means that the water level rises. Fact of fluid dynamics.

Unless the water is changing volume, there must be somewhere else that the water level falls. There is also the amount of water that evapourates or precipitates to take into consideration. I don’t believe the “Fact of fluid dynamics� explains what is happening, or will happen with sea levels.

[johnhemming2]

These are the sort of real risks that do have the potential to create havoc for the human population of the UK.

[UndercoverElephant]

Can anyone explain for me how a slowing down of AMOC raises sea levels? Serious question.

It is talking about sea levels on the eastern seaboard of the US. Usually, the flow of water away from the gulf of Mexico literally "sucks" water away from the area between the current and the US coast. If you slow it down, it sucks less.

http://www.climatecentral.org/news/east ... ream-15587

[Potemkin Villager]

Leaving aside the cooling effect this is going to have on the UK (we're about the same latitude, here in York, as Moscow is), we'll also be a LOT drier because we'll have a cold sea upwind of us. Other places with a cold sea upwind include the Namib desert and California - home of Death Valley & a load of forest fires.

We'll have to resort to using fog-catchers to collect water.

<looks out of window at interminable rain>
<sighs>

"However, it is already clear that human-caused climate change will continue to slow Amoc, with potentially severe consequences. “If we do not rapidly stop global warming, we must expect a further long-term slowdown of the Atlantic overturning,� said Alexander Robinson, at the University of Madrid, and one of the team that conducted the second study. He warned: “We are only beginning to understand the consequences of this unprecedented process – but they might be disruptive.�

A 2004 disaster movie, The Day After Tomorrow, envisaged a rapid shutdown of Amoc and a devastating freeze. The basics of the science were portrayed correctly, said Thornalley: “Obviously it was exaggerated – the changes happened in a few days or weeks and were much more extreme. But it is true that in the past this weakening of Amoc happened very rapidly and caused big changes.�

Predicting future outcomes is all based on theories which to date have all systematically underestimated every facet of climate destabilization so far observed. So maybe we could end up more towards the situation depicted in the film than comfortable to believe but without a happy ending.

I mentioned this at a presentation by an academic climatologist who went into apoplectic denial insisting that if a significant slow down occurred it would be in the"very far future" - whenever that is,

[RenewableCandy]

Have to say a proper scientist would, at that point, have admitted we have as yet no way of knowing the timescale. Non-linear effects and all that.

Mind you I think we can at least be certain that, unlike in the film, you won't have to sprint away from it...

[kenneal - lagger]

I saw a program on TV which said that the geological record showed that Northern Europe had gone from warm to cold ice age at the end of the last major ice age over a period of about 50 year in the past and put in down to an ice dam breaking in North America, forming the St Lawrence river, and dumping billions of tonnes of cold water into the North Atlantic blocking off the Gulf Stream. They called a change over 50 years rapid climate change.

Regarding the height of the sea over mean sea level, this varies considerably according the the tide, local gravitational effects, the density of the water which in turn varies according to its temperature and salinity, as well as the speed of current. It can vary up to four times a day as happens in the Solent.

[BritDownUnder]

Introducing the The Younger Dryas.

The prevailing theory is that the Younger Dryas was caused by significant reduction or shutdown of the North Atlantic "Conveyor"

Yikes.

Thermally-fractionated nitrogen and argon isotope data from Greenland ice core GISP2 indicate that its summit was approximately 15 °C (27 °F) colder during the Younger Dryas[12][15] than today.

Yikes again.

In Great Britain, beetle fossil evidence suggests that mean annual temperature dropped to −5 °C (23 °F)

Better buy some warm clothes.

Peter Huybers has argued that there is a fair confidence in the absence of the Younger Dryas in Antarctica, New Zealand and parts of Oceania.

Phew.

[kenneal - lagger]

The slowing of the rate of flow means that the water level rises. Fact of fluid dynamics.

Unless the water is changing volume, there must be somewhere else that the water level falls. There is also the amount of water that evapourates or precipitates to take into consideration. I don’t believe the “Fact of fluid dynamics� explains what is happening, or will happen with sea levels.

To add to my reply above, the area over which the Gulf Stream current flows past the East Coast of the US is relatively small compared to the area of ocean in general so a variation in height here will have little significant effect on the rest of the ocean. We were only discussing the height of the water along the eastern seaboard of the US so what happens elsewhere is an entirely different question unrelated to evaporation and precipitation.

To add to my previous reply, the atmospheric pressure locally will also affect the height of water above the mean level as in a storm surge.

[kenneal - lagger]

The maximum sea level change along the east coast of the US caused by a slowing of the Gulf Stream would occur where the Gulf Stream is constrained between Florida and the Bahamas and flows at its fastest at the moment. Thus Florida would be the worst affected area adding to the already rising sea level there.