Scientists discuss how strongly a warming Arctic is implicated in extreme weather

So the evidence is that global warming is causing an increase in extreme weather, but whether and how much the warming arctic is a direct cause is still unknown.
Of course, it doesn't have to be an either/or situation. It is likely to be a combination of effects, including warmer arctic causing a wavy jet stream and warmer Pacific ocean temperatures.

http://skepticalscience.com/scientists-discuss-how-strongly-warming-arctic-implicated-in-extreme-weather.html

May 29, 2015

The possibility that a warming Arctic could be influencing extreme weather elsewhere in the world seemed to receive a boost this week. A new paper presented further evidence linking diminishing Arctic sea ice to extreme cold winters elsewhere in the northern hemisphere.

Lead author, Prof Jennifer Francis from Rutgers University, tells us: "Our new results, together with other new studies in this field of research, are adding substantial evidence in support of the connection."

But not everyone is so sure. We asked a few scientists in the field how strong they consider the evidence linking Arctic sea ice and extreme weather to be. Here's what they told us.

Arctic amplification

The US, Canada, Japan and UK have all experienced very cold and snowy winters in recent years. In 2012, a paper by Francis and Dr Stephen Vavrus suggested that this extreme weather was a result of rapid warming in the Arctic.

Temperatures in the Arctic are increasing around twice as fast as the global average. As Arctic sea-ice diminishes, energy from the sun that would have been reflected away by sea-ice is instead absorbed by the ocean, a phenomenon known as Arctic amplification.

Francis and Vavrus suggested that warmer Arctic temperatures weaken the jet stream, a fast-flowing river of air high up in the atmosphere. The theory goes that a weaker jet stream becomes 'wavier' and leads to more persistent weather conditions, such as long cold spells in winter and heatwaves in summer.

The new paper by the same authors, published this week in Environmental Research Letters, offers further evidence to support the link.

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Scientists also haven't ruled out other factors being involved in the extreme weather, as Screen tells us:

"Correlation and trends doesn't tell you cause and effect. It is still impossible to pin the blame on the Arctic, so to speak."

A paper published in October last year, for example, finds that temperature changes in the Atlantic ocean could be triggering warm conditions in the Arctic, and cold weather over Europe and Asia. Simmonds says findings such as these mean there is still doubt regarding the Arctic's influence:

"Seen in this light, the magnitude of the direct influence of a warm Arctic on mid-latitude extremes becomes more problematic."

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tags: extreme weather