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Is the current global weather due to climate change?

February 2014
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Here in the UK they are telling us that it is not possible to link the current floods definitively to climate change. Its true us brits may be obsessed with the weather, but having endured more than two months of persistent heavy rain, powerful waves and severe storms, this is no longer the topic of small talk.

January in the south of England was the wettest since recordkeeping began more than 100 years ago and across the country the drastic conditions have devastated homes, thrown lives into confusion and fuelled a political bunfight.

The Met Office and the Centre for Ecology and Hydrology have released a report shedding light on the endless downpours and have begun to explore whether climate change is a contributing factor.

Why has the weather been so wet?

Dame Julia Slingo, the Met Office’s chief scientist said on Sunday that the UK had seen the “most exceptional period of rainfall in 248 years”.

The report reveals that while downpours and storms have not been out of the ordinary, their frequency has been.

“Each one of these individual events has not been particular outstanding, they’ve been broadly along the lines of what we would expect for a typical winter storm in the UK,” said Simon Parry from the CEH and co-author of the report. “What’s been notable about it, and different from what we’ve seen in the past, is the persistence.”

That, according to Professor Adam Scaife from the Met Office and another author of the report, is down to a series of deep low pressure systems linked to the jet stream – wind that blows from west to east across the Atlantic. “When the jet stream is strong then the storms are strong,” said Scaife.

“It’s normally stronger in winter than it is in summer but this year it has been exceptionally strong and that is absolutely bound to the storminess because the jet stream steers the storms but it also feeds off them.”

Why the abnormally strong jet stream?

The report highlights two key factors the authors believe have contributed to the effect.

The first is a persistent high pressure system lurking over a patch of the Pacific Ocean, off the west coast of North America. This high pressure system is sending a chill across the US.

“The air tends to rotate in a clockwise fashion around the high pressure system,” said Scaife. “That is going to drag the air from up near the Arctic down over North America.”

As a result, Canada and North America have been held in an icy grip for weeks. And further east, as the cold air from North America meets the warm air from the tropics, a large temperature gradient – the rate at which temperature changes with distance – is created.

“The storms feed off that temperature gradient – the stronger that gradient the more conducive it is to growing storms,” said Scaife. “As the storms grow they also flux momentum into the jet stream,” he added, “and of course sitting downstream at the end of that path is us.”

Another effect in the report is the quasi-biennial oscillation (QBO). This is where a band of fast-moving winds that blow around the equator change direction.

“You see roughly every 14 months the winds reverse and instead of blowing form the east towards the west they flip and the blow from west to east,” said Scaife.

The last time this happened was in early 2013. And while the equator is hundreds of miles away, the effects of QBO can be felt closer to home.

“When the QBO is blowing from the west then this also strengthens the jet stream over the Atlantic and increases the amount of storminess,” said Scaife. And with these winds in a strong westerly phase this winter, they too may have contributed to the relentlessly violent weather.

Is this pattern likely to be repeated in future winters?

It is hard to say at this stage. “Probably next year the QBO will have flipped but there are other factors that drive the jet stream so its not possible at this range to say whether next winter will be the same,” says Scaife.

Is climate change ultimately the cause?

It is not possible to link the current floods definitively to climate change. “In terms of the number of storms there is scant evidence that has been increasing due to climate change so far,” said Scaife. “[But] we do expect that winter rainfall is likely to increase in the future.” This is in part down to a warming planet. “As the air warms it can hold more water.”

But isn’t Global warming linked to climate change?

  • Most exceptional period of rainfall in 248 years here in the United Kingdom
  • Heaviest snowfall in Tokyo in 13 years
  • Longest cold snap and heaviest snowfall in America in decades
  • The arctic ice sheets are melting at an exceptional rate

Or is this natures way of telling us to take better care of the planet or face the consequences! What do you think? comment below.

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