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Friday, 23 May 2008
Vast cracks appear in Arctic ice By David Shukman
Environment correspondent, BBC News
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A Canadian expedition found the new cracks |
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Scientists travelling with the troops found major new fractures during an assessment of the state of giant ice shelves in Canada's far north.
The team found a network of cracks that stretched for more than 10 miles (16km) on Ward Hunt, the area's largest shelf.
The fate of the vast ice blocks is seen as a key indicator of climate change.
One of the expedition's scientists, Derek Mueller of Trent University, Ontario, told me: "I was astonished to see these new cracks.
"It means the ice shelf is disintegrating, the pieces are pinned together like a jigsaw but could float away," Dr Mueller explained.
According to another scientist on the expedition, Dr Luke Copland of the University of Ottawa, the new cracks fit into a pattern of change in the Arctic.
"We're seeing very dramatic changes; from the retreat of the glaciers, to the melting of the sea ice.
"We had 23% less (sea ice) last year than we've ever had, and what's happening to the ice shelves is part of that picture."
When ice shelves break apart, they drift offshore into the ocean as "ice islands", transforming the very geography of the coastline.
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Last year, I was part of a BBC team that joined Dr Mueller and Dr Copland as they carried out the first research on Ayles Ice Island, an iceberg the size of Manhattan.
It has since split into two, each vast chunk of ice now 400 miles (640km) south of its original position.
The rapid changes in the Arctic have reignited disputes over territory.
The Canadian military's expedition was billed as a "sovereignty patrol", the lines of snowmobiles flying Canadian flags in a display of control.
After the record Arctic melting last year, all eyes are now on what happens to the sea ice this summer.
Although its maximum extent last winter was slightly greater than the year before, it was still below the long-term average.
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A record loss of sea ice in the Arctic summer 2005 has convinced scientists that the northern hemisphere may have crossed a critical threshold beyond which the climate may never recover.
Scientists fear that the Arctic has now entered an irreversible phase of warming which will accelerate the loss of the polar sea ice that has helped to keep the climate stable for thousands of years.
Dr Serreze: "This will be four Septembers in a row that we've seen a downward trend. The feeling is we are reaching a tipping point or threshold beyond which sea ice will not recover."
Professor Wadhams: "As the sea ice melts, and more of the sun's energy is absorbed by the exposed ocean, a positive feedback is created leading to the loss of yet more ice."
"If anything we may be underestimating the dangers. The computer models may not take into account collaborative positive feedback."
"Sea ice keeps a cap on frigid water, keeping it cold and protecting it from heating up."
"Losing the sea ice of the Arctic is likely to have major repercussions for the climate."
"There could be dramatic changes to the climate of the northern region due to the creation of a vast expanse of open water where there was once effectively land."
"You're essentially changing land into ocean and the creation of a huge area of open ocean where there was once land will have a very big impact on other climate parameters."
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Climatic Research Unit : Information sheets 7: The thermohaline circulationTim OsbornWhat is the thermohaline circulation?There are three main processes that make the oceans circulate: tidal forces, wind stress, and density differences. The density of sea water is controlled by its temperature (thermo) and its salinity (haline), and the circulation driven by density differences is thus called the thermohaline circulation. The animation and list below describes the key features of the global-scale thermohaline circulation.
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 Click on image if gif does not show 11 sequences — click image to repeat |
Will the thermohaline circulation collapse?
The critical part of the thermohaline circulation (THC) is the sinking in the North Atlantic Ocean.
This occurs here (and not in the North Pacific) because the Atlantic is much more saline (and hence, denser).
It is more saline because it is warmer (more evaporation of fresh water increases the salinity of the sea water).
It is warmer in the North Atlantic because warm water is brought by the thermohaline circulation from the tropical and South Atlantic.
To some extent, therefore, the THC appears to be self-sustaining.
And if some event occurs to break this self-sustaining chain of processes, then there is the potential for the circulation to break down rapidly (i.e., over several decades) and to remain in a reduced-circulation state for several centuries.
Models from past
Some fairly simple models of the world's oceans do simulate a rapid break down of the THC, when the density of the water in the North Atlantic Ocean is lowered by adding fresh water (rain) and/or by warming.
Increased rainfall and warming over the North Atlantic are both expected as a result of increased greenhouse gas concentrations, and so it can be argued that global warming may cause a rapid collapse of the thermohaline circulation.
The self-sustaining system described above is, however, much more complex in reality, and the more complete climate models, that take some of these complexities into account, generally simulate only a gradual weakening of the THC in response to global warming.
Nevertheless, observations and palaeoclimate evidence both indicate that the THC has fluctuated both recently and in the
distant past.
When?
The majority of climate scientist believe that a critical change in the THC is unlikely to occur during this century, but the question cannot be answered with certainty at present.
Due to the potentially serious impact on our climate of a collapse of the THC, it must be regarded as a low-risk,
high-impact event that cannot be ignored.
What would happen to our climate if the thermohaline circulation collapsed?
Due to the interactions between many components of the climate system, it is not a simple matter to estimate how different our climate would be without the current thermohaline circulation.
Certainly the biggest impact would be on the temperature over the North Atlantic and Europe.
The northern North Atlantic and NW Europe have annual temperatures that are about 9 degrees C above the average for their latitude, but this cannot all be attributed to the THC, since the wind driven ocean circulation helps to transport heat
to these regions too.
This represents an upper bound on the cooling that would occur following a collapse of the THC.
Simulations with a complex climate model (see figure below, courtesy of Michael Vellinga), whose thermohaline circulation is forced into a collapse, show cooling of around 8 degrees C around the coast of Greenland, but with more moderate cooling elsewhere (less than 2 degrees C over most of Europe).
What must be remembered is that these changes will be superimposed on the pattern of warming due to the enhanced greenhouse effect.
Over Europe, then, little change or slight warming would probably be expected if the THC collapsed, with cooling restricted to the ocean areas.
Associated changes in storminess and precipitation are even harder to estimate.
Change in annual temperature 30 years after a collapse of the thermohaline circulation
Figure courtesy of Michael Vellinga, Hadley Centre.
For more information on the Climatic Research Unit click here
Last updated: July 2000, Tim Osborn |
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Thursday, 24 May 2007
Mission to Ice Island By David Shukman
BBC science correspondent, Canadian Arctic
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DAY SIX — HEADING SOUTH
We reach the Arctic staging-post of Resolute on the first stage of our journey home, all a bit stunned by a combination of adrenalin, exhaustion, sunburn and cold.
After landing on the Ice Island, we'd then had to work through the night editing our reports for the next day's broadcasts so now we all keep dozing off at every turn.
We visit Qarmartalik School here in Resolute, the hallway filled with snowboots, the corridors and schoolrooms brightly lit and decorated.
The two scientists we're with, Derek Mueller and Luke Copland, give a presentation to a class of teenagers, mostly Inuit, to explain what we've been doing.
Up on a projector screen appear images of the Arctic — the retreat of the sea ice, the temperature graphs showing the extraordinary recent warming, the break-up of the Ayles Ice Shelf now adrift as an island.
This is their land that is changing
The students seem to be spellbound — this is their land that's changing.
They ask sharp questions.
How long will it take for the Ice Island to melt? Answer — it could be years.
Where will it go?
Probably west to Alaska but it could break into chunks, one of which could even end up in the bay right here.
The principal, Brian Manning, tells me how he always encourages passing scientists and explorers to visit the school, to open the children's eyes to the world outside. |
I ask one of the teachers to write out the words "Ice Island" in Inuktitut, the Inuit language. She asks, which kind of ice?
Thin sea ice or glacial ice?
Just as there are many ways to describe snow, so there are huge differences in types of ice.
The island is actually made up of a mixture of glacial ice and old sea ice that's accumulated over many years.
The teacher consults a few others and, for the record, she settles on "aujuittuq qikiqtaq".
As we get ready for the next series of flights, we wonder at the huge interest this story has provoked.
Not all of it favourable.
We've had some very challenging questions about how we justify so much flying.
Luke Copland argues that there's a limit to what satellite analysis can tell you — only by landing on the island was it possible to measure its depth and to position the tracking beacon.
Derek Mueller agrees, and also says he has already calculated the exact mileage and offset the carbon cost with a green project in Canada.
For myself, I'll also offset the carbon cost.
But more than that, I hope we've provided a service by reporting on the first scientific research mission into the largest ice break-up in the Arctic for 40 years.
Meanwhile odd memories of the last extraordinary few days keep flashing to mind.
From the air, on our return from the island, a long thin winding trail across the icy white below had turned out to be the path of a polar bear on the hunt for seals.
At the Eureka weather station, our home for nearly a week, a short walk to stretch our legs had brought us to within a snowball's distance of a pack of Arctic wolves.
First one came by, padding over the ice, sniffing our smell and moving on; then the others, the braver ones edging a bit closer, a magical sight, but never too close.
And then the Ice Island itself — so vast, so dazzling, visited briefly and noisily, and now sliding silently across the ocean, enormous enough to become a new feature on the Arctic map but ultimately destined to vanish.
Click here to see the Canadian Ice Service website tracking the beacon we planted on the Ayles Ice Island.
DAY FIVE — LANDING ON THE ICE ISLAND
After days of waiting and fretting over satellite pictures showing confusing swirls of clouds, we take the plunge and set off for our second attempt to land on the Ice Island.
This time the clear skies over our base here at Eureka continue over the mountains and fjords and — crucially — over the sea.
I stand in the cockpit door and watch amazed as a sheet of white appears before us without a single cloud obscuring the view.
At first, it's hard to tell exactly where the Ice Island is — there's such a jumble of cracks and icebergs.
But then, one vast area of ice appears far smoother than the rest and this is confirmed as the ice island itself.
Excitement mounts as we circle at ever lower altitudes.
The pilot, Rodney Fishbrook, is searching for landing sites.
He turns in his seat and signals that we will touch down.
We buckle up very firmly — we've been warned about a bumpy landing.
When it comes, the moment is far more dramatic than I'd expected — a roar of the engines, a storm of ice around the windows, a series of violent lurches as the skis ride over the mounds of snow.
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  The Ayles Ice Island calved off the Ayles Ice Shelf in August 2005
The calving event was the largest in at least the last 25 years
A total of 87.1 sq km (33.6 sq miles) of ice was lost in this event
The largest piece was 66.4 sq km (25.6 sq miles) in area
This made the slab a little larger than Manhattan
Ayles Ice Island has moved some 50km (30 miles) since calving |
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Suddenly we're silent, stunned. Producer Mark Georgiou is the first to remember his manners and leads us in a round of applause for Rodney.
We climb out into a world of brilliant sunshine and endless white. None of us can cope without sunglasses — the glare is so intense.
The island stretches for miles around us.
The air is amazingly still — which is lucky because when we first land the temperature is minus 18.
Some of the surface is firm to walk on, other parts are deep with snowdrifts.
Jumbles of huge chunks of ice mark the areas where cracks have opened and reformed.
There are curious reminders of where the island came from.
Luke digs down and extracts a tiny lump of algae — a lifeform that grew up on what was an ice shelf and which now finds itself a passenger on a drifting island.
Derek breaks off shards of ice from under the snow and reminds me that they're 3,000 years old.
I find one thought particularly evocative: that I'm visiting an incredibly beautiful and remote part of the world which will soon vanish.
The ice that's floating beneath me will eventually melt.
And another corner of the warming Arctic will be gone forever.
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 Recent satellite images show the island free of the coast |
DAY FOUR — WAITING AT EUREKA
A day of endless white and endless waiting.
A huge depression stretching from here to the North Pole is swirling its way over us and the weather maps position the word "Low" exactly over the current location of the Ice Island we're trying to land on.
We cheer ourselves with talk of how it's bound to clear soon.
And with time on our hands we hear the tales of this lonely base, and we all enjoy this one: the tale about Eureka and stewardesses with BOAC, the forerunner of British Airways.
It's a story of longing and glamour from a more innocent age.
It turns out that in the 1960s, the polar aviation routes took many passenger planes directly over Eureka.
As the jets passed overhead, the aircrews were obliged to check in and report their positions.
Well, during the long dark winters, the weathermen down in the ice below, sheltering in the storm-battered buildings here, had a bright idea: to run a competition to find the "personality queen" among the stewardesses flying above them.
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Each time the radios crackled into life, the weathermen would crowd around and try to strike up a conversation.
It can't have been easy, with the flight crew and the entire base listening.
But this remote dialogue through the icy air was clearly popular.
I have before me an adored album of cheery letters and photographs of pretty women in miniskirts sent by the BOAC stewardesses to the Eureka base.
Wendy Madley apologises for the fact that none of them chose to send pictures of themselves in swimming costumes.
"Still," she writes, "that might prove too much for folk who are virtually womanless for such a long time!"
Margaret van der Linde asks if any of the weathermen enjoy her favourite song of the year — 1969 — which is "Sugar, Sugar", though she's not sure who it's by.
But the winning line comes from Sue Curtis, who eventually won the competition.
She begins her letter with the greeting: "Hello my deep freeze darlings!"
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She also includes some rather coy "statistics" about her height and weight, which almost certainly weren't the figures the men in the Arctic were supposed to be interested in.
Anyway, Sue Curtis stole the hearts of the Eureka staff and one of them, a technician, Ron Girardin, then aged 25, made the long journey to London to hand over a trophy to her.
An iconic black-and-white photograph shows them posing beneath the Post Office Tower.
The end of the story?
The current Eureka manager, Rai LeCoty, would love to track down any of the women who wrote to their predecessors — especially Sue Curtis.
He shows the cherished album to everyone who visits.
Has anything changed in the intervening decades?
The jets still fly overhead, the landscape is still ice-bound but I can tell this tale by email.
And for the record, Eureka's email address is: EurekaWxStn@ec.gc.ca.
DAY THREE — ICE ISLAND |
The good news is that we've flown out over the Arctic Ocean and have actually seen the ice island.
The bad news is that the cloud was too low for the pilot to attempt a landing on it.
We took off from Eureka in glorious evening sunshine and crossed a spectacular landscape of frozen valleys and mountaintops poking out through blankets of mist.
A fjord was bristling with craggy icebergs, locked in place until the summer thaw in a couple of months' time.
But as we approached the coast, we saw the first clouds.
And soon everything was obscured by a dense floor of fluffy white.
It was a depressing moment.
Just before taking off we had consulted the latest satellite images.
They had shown that the cloud was clearing to the east so in theory the island should have been clear too by the time we got there.
Instead we found ourselves descending through the cloud into a world of white, with the white ice of the sea blurring with the white of the sky.
It turns out that the weather system had not kept moving as predicted — it had stalled exactly where we didn't want it.
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And with no horizon as a guide, there would be no touchdown.
Heavy hearts all round.
With visibility so bad, it took a while to find the island.
We banked and turned and frantically checked the maps and satellite pictures.
And then an edge of it came into view, a ragged dark line separating the 3000-year-old ice of the island from the fresher ice of the frozen sea.
And then another telltale sign that we were in the right place: a line of boulders, big lumps of black, hitchhikers from the ice island's original position attached to the coast, now journeying who knows where.
We made another couple of passes, the pilot, Rodney Fishbrook, taking us down to 500ft (152m).
But with the light unchanging, he had no clear sense of the view ahead and we had no choice but to head back to Eureka, the scientists' drills untouched, the satellite tracking beacon still packed in its case, strapped to the floor of the plane.
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Even the sandwiches readied for a long night on the ice were untouched.
The Arctic is never easy, the veterans keep telling us.
No one here was too surprised that we hadn't made it first time.
Now the waiting begins again — and the obsessive scanning of the weather forecasts.
Another weather front is approaching so there'll be no chance for the next 24 hours.
But the island is just over an hour's flying time away.
The next break will see us trying again.
DAY TWO — EUREKA HIGH ARCTIC WEATHER STATION |
Today's journey takes us across unremitting miles of snow, ice and mountain, from one remote spot to an even remoter one.
We travel by that stalwart of polar aviation: the Twin Otter.
We had hoped to film what's billed as a spectacular landscape (the northern regions of Ellesmere Island), but cloud gets in the way and the throb of the engines soon sends me into the deep sleep that I didn't get last night.
The eyeshades didn't do enough to shade the midnight sun, which blazed through the curtains.
I feel a bit guilty dozing over terrain that proper explorers tackled on foot.
I've read the unnerving tales of dog teams vanishing in blizzards and ships getting crushed in the ice.
But then we land at the Eureka High Arctic Weather Station and all I feel is relief.
This is the world's northernmost, permanently manned civilian outpost, perched on the last stretch of land before the North Pole — and it's an oasis of civilisation.
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Outside it's about -10C (14F), and there's a thick drift of snow blocking our window.
We're warned to watch out for roaming polar bears and wolves.
But, inside, this community of weather forecasters, scientists and support staff is safe and well looked after.
And so are we.
Our orientation tour includes a stop at a fridge entirely devoted to ice cream.
The dinner I've heaped on my plate vanishes in an instant.
I blame the cold.
Hardly a minute passes without us thinking of the key figure in our lives right now: a weather forecaster with the Canadian Ice Service.
Trudy Wohlleben is married to one of the scientists travelling with us, Luke Copland, and she e-mails us her assessments.
We read them avidly.
It looks like the clouds will break over the ice island in the afternoon.
Good.
But that will be because the winds will accelerate.
Not so good.
I watch Luke prepare the satellite tracking beacon he's planning to plant on the island.
Suddenly we're very close to the big moment.
DAY ONE — RESOLUTE, CANADIAN ARCTIC |
It feels like we've reached the top of the world already.
Gusts of wind send snow flurries scattering across this lonely little town.
A sign says that although we've made it more than 6,000 miles (9,600km) from London, we're still 1,000 miles (1,600km) from the North Pole.
Even so, it's far enough North for the Sun never to set.
It just seems to roam around the horizon and prompts people to check that we've brought the eyeshades essential to getting any sleep here.
Another source of questioning is why on Earth we have brought luggage emblazoned with the markings of the British Antarctic Survey (BAS).
Wrong end of the planet surely?
Well, the answer is that at their Cambridge headquarters the BAS agreed to kit us out for our journey — so I'm sure we'll be warm enough but I know that explaining ourselves to everyone we meet will become a bore.
Two scientists travelling with us, Luke Copland of the University of Ottawa and Derek Mueller of the University of Alaska Fairbanks, know the score already.
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They've also agreed to our ban of another topic of conversation: the weather.
Everything about this trip hinges on clear skies and we realised early on that we could talk ourselves deep into the snowdrifts speculating about whether a break will appear when we need it.
First, we have to fly from here to the Eureka station another few hundred miles north.
And then from there we need a seemingly improbable combination of weather conditions to be able to reach our destination: the Ayles Ice Island, a monster iceberg 10 miles long and three miles across (16km by 5km), that tore away from the Arctic coastline in one of the most dramatic events of recent times, altering the very geography of this region.
Although the break-up happened in August 2005, news only emerged from scientific circles a few months ago and — until now — no scientists have had the chance to investigate this weird new structure, let alone any journalists.
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We're getting close.
Only five hundred miles to go.
But if there's heavy cloud we won't see the new island.
If there's open water around the island there could be fog which could also block our view.
If there's a strong wind, it could blow away the fog but will chill us to the core.
It's enough to make me reach for a drink.
Except that I can't — Resolute is dry, not a drop to be had apparently.
I'll just have to reach for the eyeshades instead. | |||||||
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Wednesday, 30 November 2005
Ocean changes to cool Europe By Richard Black
Environment correspondent, BBC News website
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Changes to ocean currents in the Atlantic may cool European weather within a few decades, scientists say.
Researchers from the UK's National Oceanography Centre say currents derived from the Gulf Stream are weakening, bringing less heat north.
Their conclusions, reported in the scientific journal Nature, are based on 50 years of Atlantic observations.
They say that European political leaders need to plan for a future which may be cooler rather than warmer.
The findings come from a British research project called Rapid, which aims to gather evidence relating to potentially fast climatic change in Europe.
Atmospheric radiator
The key is the Gulf Stream. After it emerges from the Caribbean, it splits in two, with one part heading north-east to Europe and the other circulating back through the tropical Atlantic.
As the north-eastern branch flows, it gives off heat to the atmosphere, which in turn warms European land.
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 The north Atlantic conveyor carries warm water to northern latitudes where it sinks, returning at depth in the ocean. |
"It's like a radiator giving its heat to the atmosphere," said Harry Bryden from the National Oceanography Centre (NOC) at Britain's Southampton University.
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"The heat it gives off is roughly equivalent to the output of a million power stations," he told reporters.
By the time it reaches the northern latitudes around Greenland and Iceland, the water has cooled so much that it sinks towards the ocean floor, a process known as "overturning".
This cooler water heads south, forming the return stream of a conveyor belt.
The complete cycle sees warm water coming northwards on the ocean's surface, and the cold water returning hundreds or thousands of metres underwater.
Florida-based scientists monitor the northwards-flowing Gulf Stream, and have found it has remained roughly constant over the last 50 years.
The NOC researchers concentrated on the colder water flowing south; and they found that over the last half century, these currents have changed markedly.
"We saw a 30% decline in the southwards flow of deep cold water," said Harry Bryden.
"And so the summary is that in 2004, we have a larger circulating current [in the tropical Atlantic] and less overturning."
And less heat, then delivered to European shores.
First evidence
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Computer models of climate have regularly predicted that the north Atlantic conveyor may well reduce in intensity or even turn off altogether, a concept that was pushed beyond credence in the Hollywood blockbuster The Day After Tomorrow.
What happens is that as Arctic ice melts and Arctic rivers flow faster — trends which have both been documented — the northern oceans become less saline.
Less salinity means a lower density; the waters then cannot sink, so the conveyor weakens.
Computer models have predicted that if it turned off completely, Europe would cool by perhaps four to six degrees Celsius.
Commenting in Nature, Detlef Quadfasel from the University of Hamburg writes that the NOC experiments provide "...the first observational evidence that such a decrease of the oceanic overturning circulation is well underway."
Natural variation
The NOC researchers admit that the case is not yet proven.
The analysis involves only five sets of measurements, made in 1957, 1981, 1992 and 1998 from ships, and in 2004 from a line of research buoys tethered to the ocean floor.
Even if the trend is confirmed by further data, it could be down to natural variability rather than human-induced global temperature change.
"This issue of variability is very important," said Harry Bryden, "and we do not have any good grasp of it.
"Models can predict it, but we think we ought to go out and measure it."
Michael Schlesinger from the University of Illinois at Urbana-Champaign, a leading expert in models of climate and ocean circulation, believes that even with these caveats, the NOC team has probably come up with a link to human-induced climate change.
"The variability question is the right one to ask," he told the BBC News website, "but the phasing is wrong."
A decade ago Professor Schlesinger showed that the north Atlantic conveyor undergoes a natural 70-year cycle of strengthening and weakening.
"The Bryden measurements are out of phase with this cycle," he said.
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"The natural cycle had a northern cooling until the mid-1970s and a warming afterwards, and here we see an apparent cooling."
He is also convinced by other details of the NOC measurements showing that the changes in the southerly underwater flow have occurred at great depths.
"The slowing down of the southward return occurs between 3,000 and 5,000m; and this more or less constitutes a smoking gun," he said.
Choosing policies
So what does all this mean for European weather? Will it necessarily get colder — or will the apparent recent trend of warmer summers continue?
"If this trend persists," said Harry Bryden, "we will see a temperature change in northern latitudes, perhaps of a degree Celsius over a couple of decades."
But climate is a complex phenomenon; other factors could conspire, even so, to produce a net warming.
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"The UK government is looking, in terms of mitigating climate change and adapting to it, at a warming scenario," said Phil Newton of the UK's Natural Environment Research Council, which funds the Rapid investigators.
"You might now be asking what sort of mitigation and adaptation they should be looking for."
To answer this question, the Rapid team plans to continue their measurements in the next few years.
Their buoys remain in place, and ships can go to gather their data as often as finance allows.
The findings will have resonance beyond the shores of the UK and Europe, as extra heat left circulating around the tropical Atlantic could have major impacts on weather systems in Africa, the Caribbean and central America.
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For archive purposes, this article is being stored on TheWE.cc website.The purpose is to advance understandings of environmental, political, human rights, economic, democracy, scientific, and social justice issues. |
Team lands on Ice Island — click here
See the Ice Island — click here
This more or less constitutes a smoking gun
