Earth Changes
There is no evidence the phenomenon - which brings a constant flow of warm water and mild weather to northern Europe - has slowed down over the past 20 years, climate scientists say.
'The changes we're seeing in overturning strength are probably part of a natural cycle,' said researcher Josh Willis, from Nasa.
The blizzard cut electricity to around 50,000 homes, while snowdrifts and fallen trees closed a large number of roads.
The police, coastguard, mountain rescue and Department of Environment launched a joint rescue operation after motorists became stranded when 3ft-high snowdrifts swept across the mountainous Glenshane Pass, a main route between Belfast and Derry.
Two evacuation centres were set up in Maghera and Dungiven in Co Derry to house the stranded, including schoolchildren whose bus had to be abandoned.

A toad is illuminated in blue light before being safely escorted across the road during its spring breeding migration in the Roxborough neighborhood of Philadelphia.
British researchers said Wednesday that they observed a mass exodus of toads from a breeding site in Italy five days before a major tremor struck, suggesting the amphibians may be able to sense environmental changes, imperceptible to humans, that foretell a coming quake.
Since ancient times, anecdotes and folklore have linked unusual animal behavior to cataclysmic events like earthquakes, but hard evidence has been scarce. A new study by researchers from the Open University is one of the first to document animal behavior before, during and after an earthquake.
The scientists were studying the common toad - bufo bufo - at a breeding colony in central Italy when they noticed a sharp decline in the number of animals at the site. Days later, a 6.3-magnitude earthquake hit, killing hundreds of people and badly damaging the town of L'Aquila.

The undersea Marsili, 9,800ft (3,000m) tall and located some 90 miles (150km) southwest of Naples, has not erupted since the start of recorded history
The Marsili volcano, which is bursting with magma, has "fragile walls" that could collapse, Enzo Boschi told the daily newspaper Corriere della Sera.
"It could even happen tomorrow," said Mr Boschi, president of the National Institute of Geophysics and Volcanology (INGV).
"Our latest research shows that the volcano is not structurally solid, its walls are fragile, the magma chamber is of sizeable dimensions," he said.
"All that tells us that the volcano is active and could begin erupting at any time."
The event would result in "a strong tsunami that could strike the coasts of Campania, Calabria and Sicily," Mr Boschi said.
The undersea Marsili, 9,800ft (3,000m) tall and located some 90 miles (150km) southwest of Naples, has not erupted since the start of recorded history.
The quake hit at 10:24 p.m. local time Tuesday, about 135 miles (215 km) from Port Blair, a city in the Andaman Islands, which is part of India, the agency said. The epicenter was about 250 miles (405 km) from Pathein, Myanmar, it said.
There were no immediate reports of damage or injuries.
The Pacific Tsunami Warning Center said there is no threat of a destructive widespread tsunami, according to historical earthquake and tsunami data, . However, the center warned that a "very small" possibility exists "of a local tsunami that could affect coasts" no more than 62 miles (100 km) from the epicenter.
"We have some historic flooding going on in places we've never had flooding before," said Cranston, Rhode Island, police Lt. Stephen Antonucci. "We have numerous streets that are closed, and they're telling us the worst is still yet to come."
All eyes were on the Pawtuxet River, which runs through Cranston. The river stood at 20.64 feet as of about 7 a.m. ET -- nearly 12 feet above flood stage of 9 feet. It is forecast to crest at 20.7 feet Wednesday morning, according to the National Oceanic and Atmospheric Administration.

Oops: A Stirling council gritting lorry got stuck in the snow after trying to pass an abandoned animal feed lorry which was itself stuck near Carronbridge, central Scotland
Up to 48,000 homes were without power as blizzards, gale-force winds and torrential rain hit both Scotland and Northern Ireland, knocking down power lines and causing widespread transport havoc.
In the worst-hit part of the province, around 300 people - including children on a school bus - had to be rescued from vehicles trapped in snow overnight on the Glenshane Pass near Londonderry.
While some parts of the UK were below freezing, temperatures in Moscow reached a mild 13c (55f).
A Greenpeace investigation has identified a little-known, privately owned US oil company as the paymaster of global warming sceptics in the US and Europe.
The environmental campaign group accuses Kansas-based Koch Industries, which owns refineries and operates oil pipelines, of funding 35 conservative and libertarian groups, as well as more than 20 congressmen and senators. Between them, Greenpeace says, these groups and individuals have spread misinformation about climate science and led a sustained assault on climate scientists and green alternatives to fossil fuels.
Greenpeace says that Koch Industries donated nearly $48m (£31.8m) to climate opposition groups between 1997-2008. From 2005-2008, it donated $25m to groups opposed to climate change, nearly three times as much as higher-profile funders that time such as oil company ExxonMobil. Koch also spent $5.7m on political campaigns and $37m on direct lobbying to support fossil fuels.
Observers have found 308 dead whales in the waters around Peninsula Valdes along Argentina's Patagonian Coast since 2005. Almost 90 percent of those deaths represent whale calves less than 3 months old, and the calf deaths make up almost a third of all right whale calf sightings in the last five years.
"This is the single largest die-off event in terms of numbers and in relation to population size and geographic range," said Marcela Uhart, a medical veterinarian with the Wildlife Conservation Society (WCS). She represents an associate director in Latin America for the WCS Global Health Program.
Comment: Once again, the British Guardian is the stalwart defender of the indefensible. This "$73 million to conservative and libertarian groups", namely right-wing political groups that jumped on the Climategate bandwagon after the man-made global warming nonsense went into free-fall, is pittance against the $7 billion (and counting) fraud reaped by the "carbon trading" scam whose existence wholly depends on the theory that humanity's carbon emissions are responsible for "warming" the planet:
European fraudsters steal $7B in carbon credit scam In fact, the above list of financial backers supporting skepticism supports our contention that the political backlash against "anthropogenic global warming" has been co-opted and will be channelled for political gain: