The Gulf Stream

I would like to acknowledge a debt of gratitude to Guy McPherson, Paul Beckwith, Sam Carana, Robertscribbler, and others in helping me to write this.

This refers to a phenomenon that is likely to be regional (affecting Britain most of all) and temporary. In the end Heat will trump.

An 'Ice Age' coming?

The weakening Gulf Stream

Seemorerocks

Yesterday the above picture was posted, of Atlantic ocean currents. It elicited the following comment from nuclear scientist Prof Chris Busby. 

“Gulf stream seems to failing. i have noticed increasingly the depressions get stuck in mid – Atlantic. we have had stuck depressions mid Atlantic since November and a continuous high over Scandinavia which means high winds and rain in England and cold easterlies [...]

Although he is not a climate scientist he is sufficiently tuned-in for some of us to take this seriously and for me to seek out some expert opinions.

This from Robertscribbler

“Absolutely true. Writing an article based on this, among other things, right now. The Gulf Stream is very weak and continues to weaken....

...The Gulf Stream has decreased in strength by about 10 to 15 percent since 2004. This is largely due to increasing melt outflows from Greenland and due to ocean current changes in the Arctic and extreme North Atlantic. Greenland melt is likely to continue to increase over the coming decades. So we should see a continued weakening and southward diversion of the Gulf Stream.”

Sam Carana of the Global Methane Emergency Group had a slightly different take

"What's important is that the Gulf Stream keeps pushing warm salty water into the Arctic Ocean, contributing to methane erupting from the seafloor of the Arctic ocean, threatening to escalate into runaway warming."

I've got no argument with either point-of-view really, but in general I am in favour of explanations that can fit in multiple explanations rather than reduce everything down to one single cause.

The Global Methane Emergency Group are doing stirling work and I cannot argue with anything other than their firm advocacy of geoengineering as a techno-fix. 

Their science is 100 per cent sound in my very humble opinion.

However, they are looking at just one positive, self-reinforcing feedback mechanism - methane release: there are many feedbacks that have been identified by Guy McPherson (I have lost count of how many - at least 25).

One of these is the weakening of thermohaline circulation.

There is today more confirmation that heat is the thing that will kill us all in the end, bringing to an end to conditions that are capable of supporting life, let alone agriculture and other aspects of human civilisation.

However, as the Arctic ice melts (and I suspect the next tipping point may be the disappearance of Arctic summer ice, replaced by dark water that absorbs, rather than reflecting sunlight) - we are sure to see a further weakening of the Gulf Stream, as well as in other areas such as the Antarctica.

This could indeed lead to a regional and temporary "ice age" before the heating takes over the entire globe.

This takes me back to the early 2000's - 2003 in particular when this scenario was first raised that melting of the Arctic ice would change the balance needed for the return of warm air to the north, giving rise to cold conditions in North America and Northern Europe.

This gave rise to a Hollywood blockbuster movie, The Day After Tomorrow which envisaged just such changes taking place, but in real time.  It was rubbished at the time on the grounds that such changes would take decades.

Now that changes in the Arctic have been unleashed and we are seeing accelerated ice melt and associated climate change, we are, to all intents and purposes, seeing changes in real time. Months and years, not decades.

The Day after Tomorrow no longer seems SO ridiculous to those of us that are capable of embracing the truth.

The problem is that, in general we have such short memories.  Most people can only remember what happened yesterday - not much further back than that.

Back in 2003 two scientists, Peter Schwartz and Doug Randall, published a paper, An Abrupt Climate Change Scenario and Its Implications for United States National Security.

This laid out the scenario of abrupt climate change for the first time.

Below are several articles, from the redoubtable the Guardian,  dating from 2003, discussing in terms that are understandable the scenario of a rapid shutdown of the Gulf Stream

Will global warming trigger a new ice age?

If climate change disrupts ocean currents, things could get very chilly round here, reports Bill McGuire

the Guardian,
13 November, 2003

If you can remember back to the bitter winters of the late 1970s and early 80s you might also recall that there was much discussion in scientific circles at the time about whether or not the freezing winter conditions were a portent of a new ice age.

Over the past couple of decades such warnings have been drowned out by the great global warming debate and by consideration of how society might cope in future with a sweltering planet rather than an icebound one. Seemingly, the fact that we are still within an interglacial period, during which the ice has largely retreated to its polar fastnesses, has been forgotten - and replaced with the commonly-held view that one good thing you can say about global warming is that it will at least stave off the return of the glaciers.

Is this really true, or could the rapidly accelerating warming that we are experiencing actually hasten the onset of a new ice age? A growing body of evidence suggests that, at least for the UK and western Europe, there is a serious risk of this happening - and soon.

The problem lies with the ocean current known as the Gulf Stream, which bathes the UK and north-west Europe in warm water carried northwards from the Caribbean. It is the Gulf Stream, and associated currents, that allow strawberries to thrive along the Norwegian coast, while at comparable latitudes in Greenland glaciers wind their way right down to sea level. The same currents permit palms to flourish in Cornwall and the Hebrides, whereas across the ocean in Labrador, even temperate vegetation struggles to survive. Without the Gulf Stream, temperatures in the UK and north-west Europe would be five degrees centigrade or so cooler, with bitter winters at least as fierce as those of the so-called Little Ice Age in the 17th to 19th centuries.

The Gulf Stream is part of a more complex system of currents known by a number of different names, of which the rather cumbersome North Atlantic Meridional Overturning Circulation (Namoc) is probably the most apt. This incorporates not only the Gulf Stream but also the cold return currents that convey water southwards again. As it approaches the Arctic, the Gulf Stream loses heat and part of it heads back to warmer climes along the coast of Greenland and eastern Canada in the form of the cold, iceberg-laden current responsible for the loss of the Titanic. Much, however, overturns - cooling and sinking beneath the Nordic seas between Norway and Greenland, before heading south again deep below the surface.

In the past, the slowing of the Gulf Stream has been intimately linked with dramatic regional cooling. Just 10,000 years ago, during a climatic cold snap known as the Younger Dryas, the current was severely weakened, causing northern European temperatures to fall by as much as 10 degrees. Ten thousand years before that, at the height of the last ice age, when most of the UK was reduced to a frozen wasteland, the Gulf Stream had just two-thirds of the strength it has now.

What's worrying is that for some years now, global climate models have been predicting a future weakening of the Gulf Stream as a consequence of global warming. Such models visualise the disruption of the Namoc, including the Gulf Stream, as a result of large-scale melting of Arctic ice and the consequent pouring of huge volumes of fresh water into the North Atlantic, in a century or two. New data suggest, however, that we may not have to wait centuries, and in fact the whole process may be happening already.

So that the warm, saline surface waters of the Gulf Stream can continue to push northwards, there must be a comparable, deep return current of cold, dense water from the Nordic seas. Disturbingly, this return current seems to have been slowing since the middle of the last century. Bogi Hansen at the Faroese fisheries laboratory, and colleagues in Scotland and Norway, have been monitoring the deep outflow of cold water from the Nordic seas as it passes over the submarine Greenland-Scotland ridge that straddles the North Atlantic at this point. Their results show that the outflow has fallen by 20% since 1950, which suggests a comparable reduced inflow from the Gulf Stream.

Although there is as yet no direct substantiation of this, and his colleagues point to reports of the cooling and freshening of the Norwegian Sea and to temperatures that are already falling in parts of the region as possible evidence of contemporary Gulf Stream weakening.

It also seems that it is not only the intensity of the outflow of cold water that is changing. Bob Dickson of the Centre for Environment, Fisheries, and Aquaculture Science at Lowestoft, and colleagues, have reported a sustained and widespread freshening of returning deep waters south of the Greenland-Scotland ridge, which appears to have been going on for the past three or four decades.

Already the freshening is extending along the North American eastern seaboard towards the equator, in the so-called Deep Western Boundary current.

One of the scariest aspects of the current dramatic changes occurring in the system of North Atlantic currents is that the deep, southward-flowing limb of the Namoc can be thought of as representing the headwaters of the worldwide system of ocean currents known as the Global Thermohaline Circulation. The possibility exists, therefore, that a disruption of the Atlantic currents might have implications far beyond a colder UK and north-west Europe, perhaps bringing dramatic climatic changes to the entire planet.

Yet again, this highlights the fact that global warming, for which we have only ourselves to thank, is nothing more nor less than a great planetary experiment, many of the outcomes of which we cannot predict. Wallace Broecker, an ocean circulation researcher at New York's Lamont-Doherty Earth observatory, described the situation perfectly when he pointed out that "climate is an angry beast and we are poking at it with sticks". Let's hope that when it truly turns on us, its teeth don't match its outrage.

· Bill McGuire is Benfield Professor of Geophysical Hazards and director of the Benfield Hazard Research Centre at University College London. He will appear on BBC2 Horizon's The Big Chill tonight

Alarm over dramatic weakening of Gulf Stream

The powerful ocean current that bathes Britain and northern Europe in warm waters from the tropics has weakened dramatically in recent years, a consequence of global warming that could trigger more severe winters and cooler summers across the region, scientists warn today

Interactive guide to the Gulf Stream

the Guardian,

1 December, 2005

Researchers on a scientific expedition in the Atlantic Ocean measured the strength of the current between Africa and the east coast of America and found that the circulation has slowed by 30% since a previous expedition 12 years ago.

The current, which drives the Gulf Stream, delivers the equivalent of 1m power stations-worth of energy to northern Europe, propping up temperatures by 10C in some regions. The researchers found that the circulation has weakened by 6m tonnes of water a second. Previous expeditions to check the current flow in 1957, 1981 and 1992 found only minor changes in its strength, although a slowing was picked up in a further expedition in 1998. The decline prompted the scientists to set up a £4.8m network of moored instruments in the Atlantic to monitor changes in the current continuously.

The network should also answer the pressing question of whether the significant weakening of the current is a short-term variation, or part of a more devastating long-term slowing of the flow.

If the current remains as weak as it is, temperatures in Britain are likely to drop by an average of 1C in the next decade, according to Harry Bryden at the National Oceanography Centre in Southampton who led the study. "Models show that if it shuts down completely, 20 years later, the temperature is 4C to 6C degrees cooler over the UK and north-western Europe," Dr Bryden said.

Although climate records suggest that the current has ground to a halt in the distant past, the prospect of it shutting down entirely within the century are extremely low, according to climate modellers.

The current is essentially a huge oceanic conveyor belt that transports heat from equatorial regions towards the Arctic circle. Warm surface water coming up from the tropics gives off heat as it moves north until eventually, it cools so much in northern waters that it sinks and circulates back to the south. There it warms again, rises and heads back north. The constant sinking in the north and rising in the south drives the conveyor.

Global warming weakens the circulation because increased meltwater from Greenland and the Arctic icesheets along with greater river run-off from Russia pour into the northern Atlantic and make it less saline which in turn makes it harder for the cooler water to sink, in effect slowing down the engine that drives the current.

The researchers measured the strength of the current at a latitude of 25 degrees N and found that the volume of cold, deep water returning south had dropped by 30%. At the same time, they measured a 30% increase in the amount of surface water peeling off early from the main northward current, suggesting far less was continuing up to Britain and the rest of Europe. The report appears in the journal Nature today.

Disruption of the conveyor-belt current was the basis of the film The Day After Tomorrow, which depicted a world thrown into chaos by a sudden and dramatic drop in temperatures. That scenario was dismissed by researchers as fantasy, because climate models suggest that the current is unlikely to slow so suddenly.

Marec Srokosz of the National Oceanographic Centre said: "The most realistic part of the film is where the climatologists are talking to the politicians and the politicians are saying 'we can't do anything about it'."

Chris West, director of the UK climate impacts programme at Oxford University's centre for the environment, said: "The only way computer models have managed to simulate an entire shutdown of the current is to magic into existence millions of tonnes of fresh water and dump it in the Atlantic. It's not clear where that water could ever come from, even taking into account increased Greenland melting."

Uncertainties in climate change models mean that the overall impact on Britain of a slowing down in the current are hard to pin down. "We know that if the current slows down, it will lead to a drop in temperatures in Britain and northern Europe of a few degrees, but the effect isn't even over the seasons. Most of the cooling would be in the winter, so the biggest impact would be much colder winters," said Tim Osborn, of the University of East Anglia climatic research unit.

The final impact of any cooling effect will depend on whether it outweighs the global warming that, paradoxically, is driving it. According to climate modellers, the drop in temperature caused by a slowing of the Atlantic current will, in the long term, be swamped by a more general warming of the atmosphere.

"If this was happening in the absence of generally increasing temperatures, I would be concerned," said Dr Smith. Any cooling driven by a weakening of the Atlantic current would probably only slow warming rather than cancel it out all together. Even if a slowdown in the current put the brakes on warming over Britain and parts of Europe, the impact would be felt more extremely elsewhere, he said.

Climate change: Gulf stream collapse could be like a disaster movie

The next Ice Age could take only weeks to engulf Britain. Scientists say the last great disruption to the Gulf Stream 12,800 years ago took only a couple of months to trigger a massive plunge in temperatures across Europe.

Robin McKie, Science Editor

,

the Observer,

29 November 2009

"It was as if Europe had been shifted 20 degrees north and Ireland moved to Svalbard," said Bill Patterson of Saskatchewan University.

In the Hollywood blockbuster The Day After Tomorrow, an Ice Age was set off in a single day when the Gulf Stream was disrupted. "That is silly," said Patterson. "It couldn't happen that quickly. However, previous estimates that it would take decades to switch off the Gulf Stream are not backed by our work. It could happen in a couple of months."

The Gulf Stream carries tropical heat from the Caribbean to northern Europe but is already being disrupted by meltwater pouring from the Arctic as global warming intensifies. One day it may switch off completely, say scientists.

Such an event occurred 12,800 years ago when a vast lake – created from melting glaciers at the end of last Ice Age – overflowed and poured into the north Atlantic, blocking the Gulf Stream. Europe froze – almost instantly, said Patterson.

His team analysed mud samples from Lough Monreagh in Ireland and discovered layers of white sediment made up of calcite crystals from algae. "Then abruptly the sediment turned black. This stuff contained no biological material." In other words, all life in the lake had been extinguished in less than three months. "It was very sudden," added Patterson, "and it could happen again."

New updates for earth.nullschool.net! Now you can see global ocean surface currents in near real-time. Just click here:


http://earth.nullschool.net/#current/ocean/surface/currents/orthographic


(A browser refresh may be required to pick up the changes.)

Earth & Space Research in Seattle, WA, produces this data every five days as part of the OSCAR project:

http://www.esr.org/oscar_index.html

Also see this - 

The Antarctic Half of the Global Thermohaline Circulation Is Faltering' (April, 2013)

The sudden cooling of Europe, triggered by collapse of the global thermohaline circulation in the north Atlantic and the slowing of the Gulf Stream has been popularised by the movies and the media. The southern half of the global thermohaline circulation is as important to global climate but has not been popularised. The global oceans' coldest water, Antarctic bottom water forms in several key spots around Antarctica. The water is so cold and dense that it spreads out along the bottom all of the major ocean basins except the north Atlantic and Arctic. Multiple recent reports provide strong evidence that the formation of Antarctic bottom water has slowed dramatically in response to massive subsurface melting of ice shelves and glaciers. The meltwater is freshening a layer of water found between depths of 50 and 150 meters. This lightened layer is impeding the formation of Antarctic bottom water, causing the Antarctic half of the global thermohaline circulation to falter