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
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.
The US, Canada, Japan and UK have all
experienced very cold and snowy winters in recent years. In 2012,
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
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
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
The new paper by the same authors, published
this week in
Environmental Research Letters, offers further
evidence to support the link.
Jet stream waviness
Francis and Vavrus' work triggered what has
lively area of research. One of the
difficulties with the theory proposed is that it's very hard to
measure the 'waviness' of the jet stream directly. Instead, Francis
and Vavrus use a number of metrics to measure it in other
One method tries to see the mechanism in action by looking for
evidence of temperature differences causing wind patterns to change
and the jet stream to get wavier. Another way looks at whether
these wavy jet stream patterns are occurring more frequently across
the northern hemisphere.
Identifying these patterns of waviness is
important because they lead to 'blocking', which causes cold
weather patterns to hold on for longer. In the 2013-14 US winter,
the prolonged spell of very cold weather caused 91 per
cent of the Great Lakes to freeze over.
Francis says we're seeing more of this
persistent extreme weather as the Arctic warms up:
"Occurrence of these
events has increased during recent decades when Arctic
amplification has emerged as a strong signal."
Arctic amplification is greatest in autumn and
winter (see graph below), which is why it mainly results in
persistent cold weather events, Francis explains.