In streets that would normally be bustling with shoppers, the only sound is the thrum of helicopters overhead and the surreal lapping of water against walls. There is an air of awe and disbelief amongst the other locals I meet, as we gawp at cars submerged in dirty brown water, and watch as residents wearing waders attempt to rescue belongings.

York is used to floods – the river Ouse usually bursts its banks once or twice a year – but this is well beyond our normal experience. Huge chunks of the city centre have become islands, and large swathes are cut off from each other by fierce new rivers, pouring down residential streets. People have been stoic and calm in the face of this disaster, but there is also anger, and a sense of feeling that these floods were not just down to bad luck.

“Rhododendrons flowering in December and a flooded house – any correlation do you think?” asks Selena Whitehead, whose house was inundated by the river Ouse on Sunday. And of course it is not just York that has suffered.

First Desmond, then Eva and now Frank: three major storms have slammed into northern England, dumping record amounts of rainfall and causing flooding misery, all within the space of just one month.


Special combination

Now climate scientists are saying this isn’t simply bad luck; it’s driven by a combination of global warming and unusual ocean conditions. Worse still, this intense stormy pattern could have a few years to run.

Jennifer Francis, an atmospheric scientist at Rutgers University in New Brunswick, New Jersey, has previously shown that the rapid warming in the Arctic is making the jet stream – the high-level river of air that snakes around the northern hemisphere – more wavy. The warmer Arctic has made the north-south air temperature contrast smaller, which weakens the jet stream, and makes it more prone to being deflected by obstacles in its path, such as mountains or anomalies in ocean temperatures.

Now the UK is starting to feel the full impact of this wavy jet stream, thanks to an unusual cool patch of water in the North Atlantic, probably created by excess melting of the Greenland ice sheet. This winter, the jet stream has been skirting around the bottom of this cold North Atlantic blob and then aligning itself in a south-west to north-east direction, placing northern England right in the crosshairs.

And, as recent weeks have shown, this wavy jet can easily become jammed in place, firing storm after storm at the same locations. “Ocean temperature anomalies tend to persist for months to years, so it wouldn’t surprise me to see the UK dealing with stormy conditions for a few years,” says Francis.

Add to this the powerful effect of another ocean anomaly – the El Niño, which is causing weather havoc all over the world – and it is easy to see why the weather is so out of kilter this year.

Across the pond

Over on the other side of the North Atlantic, people have also been dealing with the fallout from a wavy jet stream. An unusually warm patch of ocean off the west coast of the US has added an extra kink to this high-level wind. The north-west of the country has been caught under freezing polar air to the north of the jet stream, while the south and east coast has been sweltering in unseasonably warm tropical air, to the south of the jet stream. And where the two air masses meet, powerful tornadoes have been spinning up, flattening houses and flinging cars into the air, killing scores of people.

Meanwhile, rising global temperatures, which lead to the atmosphere holding more moisture, are only making matters worse. “The additional atmospheric moisture causes deluges to become even more intense,” says Richard Allan, a meteorologist at the University of Reading, UK.

This is backed up by preliminary results from thousands of computer simulations of storm Desmond’s flooding event, carried out by researchers at the University of Oxford and the Royal Netherlands Meteorological Institute (KNMI), suggesting that such heavy rainfall is now 40 per cent more likely to happen than in the past because of global warming.

“I don’t think there has been a combination of conditions similar to the one we’re seeing now because Arctic sea ice loss along with the very warm Arctic are the ‘new game in town’, caused by high greenhouse gas concentrations,” says Francis. “It’s safe to say we’re in uncharted territory.”

Read more: “Storm warning: The winds of climate change“

Image credit: Anna Gowthorpe/PA Wire/Press Association Image