The not-so-strange paradox of global warming's northern freeze

 

OPI NION:The thaw is on (apparently); can this year’s two extreme cold snaps be linked to wider climate change?

AS 2010 draws to a close, globally it will enter the record books as a year of weather extremes. It is certain to be among the three hottest years since accurate global instrumental records began in 1850, and, despite the current cold spell over much of northern Europe, may well turn out to be the hottest.

The decade 2000-2009 has already been confirmed as the hottest yet recorded globally. The two regions now bearing the brunt of the heating are the Arctic/Greenland and sub-Saharan Africa.

The number and intensity of weather-related disasters so far in 2010 is also notable. In July and August, Pakistan experienced the worst flooding in its history, with over 20 million people forced from their homes and 1,500 deaths. This year, western India and China experienced their worst monsoon flooding since 1998. Landslides claimed over 1,400 lives in China’s Gansu province.

Meanwhile, Russia was this summer gripped by a record heatwave, with mean July temperatures 7.6C above normal. An estimated 11,000 heat-related deaths were recorded in Moscow alone. Some years ago, Russian president Vladimir Putin joked that global warming would be good for his country, as people would have to buy fewer fur coats. “The climate is changing. This year we have come to understand this,” a clearly chastened Putin said in July.

Last winter’s intense cold spell over northern Europe and much of the US was mainly attributed to a phenomenon known as the Arctic oscillation, in which a region of high pressure over the Arctic forced down bitterly cold air over northern Europe. The freeze persisted as a result of a “blocking anticyclone” that kept our usual wet and wild Atlantic weather at bay.

The upper northern hemisphere chill was “a series of weather events happening simultaneously, well below the climate scale”, according the US National Climatic Data Centre. However, the unexpected reappearance of intensely cold weather over northern Europe has led to fears the Gulf Stream, which delivers as much winter heat energy to western Europe as the sun, may be weakening.

However, the UK’s Met Office recently reported that concerns for the Atlantic Conveyor are misplaced. “This is an atmospheric effect and is not due to a slowdown of ocean circulation,” said a spokesman. Dr Gerald Fleming of Met Éireann is equally cautious, although he does point out that “two exceptionally cold periods like we’ve experienced in the last 12 months is pretty well unprecedented in around a century of Met Éireann records”. These conditions are, he states: “very much at the edge of the range of normalities”.

Recent research on declining Arctic sea ice levels suggests that the loss of significant ice cover in the Barents-Kara Sea, north of Norway and Russia is paradoxically enhancing the chilling effect of the North Atlantic Oscillation. This study, published in the Journal of Geophysical Research, argues that dramatic warming in the Arctic is leading to rapidly shrinking ice cover, which in turn leads to a loss of ocean heat and a warming of the lower atmosphere.

This warming may be triggering circulation anomalies that are leading to overall northern hemisphere cooling. The computer modelling used in the research points towards a trebling of the probability of cold winter extremes in Europe and northern Asia fuelled by ice cover losses in the Arctic. If this turns out to be correct, “global warming” could ironically lead to sharp regional cooling and far more frequent harsh winters here in Ireland, despite the underlying heat signal, in the decades ahead.

Dr Conor Murphy of the Irish Climate Analysis and Research Unit at NUI Maynooth is more guarded: “the current cold conditions, as with earlier last January, are due to the presence of blocking anticyclones in the Atlantic that prevent milder westerly winds from entering this part of Europe.”

He points to research from the University of Reading suggesting that these “blocking anticyclones” appear to be related to recent low sunspot activity through alterations in the high-level air current called the jet stream. “The same sunspot activity has been used incorrectly by climate sceptics to argue against the human role in changing global climate!”

The dramatic weather events which have battered Ireland in the last 24 months, cannot in themselves be extrapolated to either “prove” or “disprove” man-made climate change.

However, when viewed against a global canvas of record high temperatures, droughts, unprecedented Arctic and glacial ice melt, flood events and a marked increase in “weather anomalies”, a more ominous picture emerges.

It remains a physical impossibility that continuing to pump 27 billion tonnes of the heat-trapping gas, CO2, every year into the atmosphere could do anything other than ratchet up the global thermostat. In a rapidly warming world, we may soon need to cope with the inevitable as much as the unpredictable.


John Gibbons is a specialist environmental writer and blogs at ThinkOrSwim.ie