First, the good news: despite concerns, the Gulf Stream, the powerful current that transfers vast amounts of heat from the equator to north-western Europe, does not appear to be faltering. Were it to stop entirely, average winter temperatures in Ireland would plummet by 5ºC, meaning the recent freeze would be a regular fixture for several months every year.
Germany's Potsdam Institute for Climate Impact Research warned that the marked overall warming of the earth's northern half could counterintuitively result in significantly colder winters. Dramatic losses of sea-ice in the eastern Arctic is affecting far more than polar bears. It is also causing regional heating of the lower levels of air – this in turn is leading to strong anomalies in atmospheric airstreams, triggering an overall cooling of the northern continents. This is the conclusion of a study recently published in the Journal of Geophysical Research. Think of the Arctic ocean as a cup of take-out coffee, and the ice sheet as the lid. Take off the lid, and the coffee cools quickly – but the heat loss from the liquid transfers to the atmosphere.
"These anomalies could triple the probability of cold winter extremes in Europe and northern Asia," said Vladimir Petoukhov, lead author of the study. "Recent severe winters like last year's or the one of 2005-'06 do not conflict with the global warming picture, but rather supplement it."
Tellingly, this statement was issued in early November, well ahead of the current freeze. Professor John Sweeney of NUI Maynooth, Ireland's top climate specialist, is aware of the Potsdam Institute research, but cautioned about extrapolating from what remain weather, rather than climate, events: "More extreme weather events are likely when you put more energy into the system.".
Ironically, if the intense 'blocking anticyclone' that is keeping our usual maritime weather at bay and delivering this freezing weather were instead happening in mid-summer, "we'd now be in the middle of a heatwave, and running out of water from that", added Sweeney.
Global warming is ratcheting up energy in the global climate system, and this is expressing itself in the ever-increasing number and intensity of what we used to call 'natural disasters' – floods, droughts, landslides, forest fires etc. The year of 2010 seems certain to be globally the hottest since instrumental records began in the mid-19th century. While Europe shivers, temperatures in western Greenland are currently an astonishing 10ºC above normal.
"By global warming destroying the Arctic ice sheet, we've essentially changed the climate of north-western Europe, and that simply has to have an effect," said Dr Kieran Hickey of NUI Galway. "Climatically, we're moving into unknown territory; when the climate is changing rapidly, you get lots of extremes – look at the flooding and freezing events of the last two or three years. The climate is clearly out of equilibrium."
The fear among scientists is that humanity is stumbling towards a climatic tipping point and into a future where weather extremes are once again the dominant force in shaping the course and setting severe limits to human progress.