Don’t try telling anyone between Boston and Beijing about global warming; they might just hit you with a snow shovel.
The worst blizzards in decades have struck across the northern hemisphere. Seoul, the capital of South Korea, has had 27cm of snow in a day – the heaviest fall since records began more than 70 years ago. European countries from Britain to Poland are bracing themselves for a record-breaking cold snap, while plunging temperatures have already claimed many victims in India. In the extreme north of China, temperatures have dipped as low as minus 32°C.
Nor is it only the northerly latitudes that are experiencing bizarre weather. After years of drought, parts of Australia are now being declared natural disaster zones after torrential rainfall caused rivers to rise by several metres, triggering floods. Even the normally placid climes of the UAE have experienced upheaval, with rainfall reaching near-record levels.
So what was all that about global warming, with searing heat and endless drought? Surely it has now been exposed as nothing but anti-capitalist scaremongering. Not according to the head of the Beijing Meteorological Bureau, who declared the freezing temperatures in his city to be the result of unusual atmospheric patterns caused by global warming.
We should be wary about ascribing any spate of odd weather to a long-term change in the climate, but the current conditions are certainly linked to unusual atmospheric patterns. Indeed, they highlight the power of these patterns to cause global chaos – and their critical importance for understanding the future climate of our planet.
The existence of these natural fluctuations in the world’s weather systems was recognised long before today’s obsession with man-made global warming. Known by esoteric names such as the Pacific Decadal Oscillation (PDO) and the North Atlantic Oscillation (NAO), each has the power to trigger different patterns of weather.
The current severe conditions in the northern hemisphere are principally the result of the so-called Arctic Oscillation (AO) – the seesaw-like behaviour of the relative atmospheric pressure between the north polar region and mid-latitudes of around 40° north. The difference in pressure between these two regions affects the winds – and thus the weather systems – that sweep across the northern hemisphere.
Since the late 1970s, the AO has generally been in its so-called positive state, with relatively low pressure over the Arctic and high pressure further south. In that state, the AO typically brings relatively dull, mild and wet winters to northerly latitudes. But now the AO has turned very sharply negative, reaching depths not seen for 30 years – with consequences all too apparent to millions of people.
Quite why the AO flips from one state to another is not fully understood – and may never be. Like so much else about the climate, it’s the end-result of myriad factors from ocean currents to wind systems, all interacting with each other in ways that defy analysis. Records of its behaviour over the decades look like the outcome of tossing a coin, and attempts to predict its behaviour have met with little success.
Even so, the current extraordinary weather shows we cannot dismiss these natural climate flips as bit-players in the grand drama of global climate change.
At the very least, we must recognise their ability to deceive us. During the late 1960s, a run of bitterly cold winters prompted stories of the world sliding into a new Ice Age. In reality, the cause was merely a brief run of negative AOs, bringing the kind of winter weather now blighting many countries. After a few years, the AO flipped back into positive mode again, bringing warmer winters and an end to talk of polar bears in Trafalgar Square.
To argue that the current cold temperatures disprove global warming is to make the same mistake: the AO could flip back again at any time, returning us to life in a steadily warming planet.
But global warming sceptics are not alone in being fooled by short-term climate blips. The rapid warming of the planet in the late 1990s was seized on by environmentalists as final proof that the world faced climatic catastrophe. In reality, much of the heating was the result of an extraordinarily strong outbreak of the so-called El Nino-Southern Oscillation (ENSO), in which warm water in the Pacific races toward the South American coast, triggering climatic upheaval on a global scale. More recent outbreaks of the ENSO have been milder, resulting in much less dramatic rises in global temperature.
The upshot of these examples is clear: don’t read too much into outbreaks of weird weather. Most probably they are just the result of entirely natural flips in well-known climate patterns. Genuine climate change can be gauged only over timescales of several decades or more.
But it would also be a mistake to think that these flips can’t have long-term effects. New research suggests that every so often they can come into synch with each other, triggering fundamental changes to the climate. There is evidence that for the past decade they have worked against global warming, halting the rise in temperatures. But calculations suggest that over the next decade or so they may move out of synch and start to boost global warming – with unknown consequences.
The current turmoil in the world’s climate should thus be seen as a warning to focus more attention on the power of natural weather patterns. They hold the key to the future climate of this planet, and it is vital that we understand what they are going to do next.
Robert Matthews is Visiting Reader in Science at Aston University in the UK