The first signs are so subtle they’re barely perceptible, like the start of a Hollywood disaster movie. Fishermen off the coast of Peru notice the tides are a little higher than normal, a local beachcomber finds the Pacific waves lapping at her feet distinctly warmer than usual and farmers grow concerned about encroaching storms. Soon people across the world realise something is wrong with the climate. Weather records for everything from floods to droughts start toppling, and destruction and fatalities mount.
The cause appears to be obvious: climate change triggered by man-made global warming. But then, after more than a year of turmoil, it stops – and the real culprit becomes clear. It’s a weather phenomenon whose name belies its power: El Niño – Spanish for ‘the little boy’.
El Niño – or the El Niño-Southern Oscillation (ENSO) to give it its full title – is so-named because of its habit of appearing around the Christmas festivities marking the birth of Christ. It is the most notorious of a family of weather patterns that can wreak global havoc. Understanding their cause is now the focus of intense research – not least because of the need to prepare for what these patterns might do.
Climate Change Conspiracy
Every so often, around every three to eight years in El Niño’s case, these patterns trigger severe weather around the globe causing billions of pounds worth of damage.
But now scientists believe that weather patterns like El Niño can do more than just inflict occasional mayhem. Evidence is emerging that they conspire together to cause wholesale changes in the climate- and could soon unleash global mayhem.
Scientists have long known that our climate is subject to a host of influences, both near and far. Some are literally cosmic in origin: the gravitational effects of the Sun, Moon and neighbouring planets affect the orbit and tilt of the Earth, causing cyclic changes in the heat it receives from the Sun. These ‘Milankovitch cycles’, which range from around 20,000 to over 100,000 years in length, are thought to drive the ebb and flow of the Ice Ages. As such, they have influenced human evolution, driving early humans to develop tools, clothing and agriculture in order to cope with the changing environment.
Weather patterns like El Niño have had dramatic effects far more recently too. The bitterly cold Russian winters that defeated Napoleon in 1812 and Hitler in 1942 have both been linked to El Niño phenomena in the Pacific. Many in Britain still recall the winter of 1962-63, when temperatures plunged to -16ºC across the nation for weeks on end, causing even the sea to freeze. Scientists attribute this record-breaking winter to the North Atlantic Oscillation (NAO), a pattern of atmospheric pressure that influences winter weather over Europe and is linked to this year’s cold snap.
El Niño and the NAO are suspected of being key players in the most important climatic issue of our time: global warming. According to most scientists, the average temperature of the Earth is being driven up by man-made greenhouse gases. It has not been a relentless increase, though: the last 150 years have seen many ups and downs. And, over the last decade, the rise in temperature has all but ceased.
These fluctuations have led to claims that global warming is a natural phenomenon, with no link to human activity. But climate scientists suspect the real explanation lies in patterns like El Niño, which may be conspiring to mask the real level of global warming. They point out that the severe El Niño event that struck in 1997-98 caused a jump in global temperature much higher than the underlying trend – making subsequent rises seem less dramatic. “The issue is one of timescales,” says climate expert Prof Richard Williams of the University of Liverpool. “Global warming can only reliably be inferred over a timescale of several decades.”
But why have global temperatures remained relatively static since the last major El Niño event? New research points to a disturbing possibility. Analysis of past climate data by a team led by Prof Anastasios Tsonis of the University of Wisconsin, Milwaukee, has revealed connections between El Niño, the NAO and two other weather patterns: the Pacific Decadal Oscillation (a periodic flip in the temperature of the northern Pacific) and the Northern Pacific Index (an effect akin to the NAO). Tsonis has found that all these patterns come into sync every few decades. And when they do, Earth’s climate flips from periods of warming to cooling, and vice versa.
According to Tsonis, the patterns came into sync during the late 1970s, triggering a flip in the climate that resulted in a period of relatively fast warming. Significantly, however, they came into sync again around the turn of the millennium – and currently seem to be helping to offset global warming.
Tsonis likens the effect to a pacemaker that operates all the time, regardless of the underlying warming effect. “It is this mechanism that causes shifts such as the recent cooling,” he says. “It does not, however, imply that the long-term trend has disappeared.” What it does imply is distinctly disturbing: for the last decade we have been shielded from the full force of man-made global warming by a quirk of weather patterns.
So just how long do we have before the patterns flip back again, and start boosting global warming? “Judging from previous shifts, for the next 20 years or so we may be cooling – or at least not warming,” says Tsonis. “What will happen after that is unknown.”
Unsurprisingly, his team’s conclusions are hotly debated. Some remain sceptical: “There’s a lot of interest, but little conclusive evidence,” says Williams. Others think the role of El Niño and the other weather patterns in climate change have to be taken seriously, but that their effects are short-lived.
“We agree that effects like El Niño can temporarily alter the rate of global warming,” says Dr Adam Scaife of the Met Office. “But with increasing levels of greenhouse-gas emissions, the rate of warming will increase afterwards.”
If these new findings are correct, we may thus be living through the calm before a potential climatic storm. No-one yet knows when this period of grace will end, but it seems we may already be a decade into it. We should not count on staying shielded for much longer.
Robert Matthews is a visiting reader of science at Aston University.