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Friday, April 19, 2013

Peter Sinclair: Jet Stream Blows Winds of Change

by Peter Sinclair, Climate Denial Crock of the Week, April 19, 2013

I’ve been recovering from earth-month speaking-event whiplash, having criss-crossed the state over recent days to talk about climate change, and what scientists are telling us.

Meanwhile, Paul Douglas, above, gave a brief summary of what we know about the extreme spring in the US, just before the current river of moisture hit across the nation’s midsection last night.

Near record setting flooding is hitting at my location, schools closed and evacuations underway.  I got a bump from Jeff Masters last night about the situation, he is grappling with the big picture, will be posting more later today.  For now, more concern about extreme weather knock-on effects – possible washing of dangerous invasive species into the Great Lakes water system.

The rains have brought the Des Plaines River on the east side of Chicago to major flood stage this morning, and a record flood crest is expected on Friday. The Asian Carp, a dangerous invasive species that would cost billions of dollars were it to get loose in the Great Lakes, is present in the Des Plaines River. Today’s flood event is capable of washing significant numbers of Asian Carp from the Des Plaines River into a canal that feeds directly into Lake Michigan, where they might be able to set up a breeding population capable of devastating the Great Lakes’ fishing industry. However, in October 2010, the U.S. Army Corps of Engineers completed the Des Plaines River barricade, a 13-mile-long system of concrete barriers and a specially fabricated wire mesh that allows water to flow through the fence but prevents the passage of fish. Hopefully, this barricade will withstand the flood and prevent Asian Carp from washing into Lake Michigan.
CarbonBrief reports on similar extremes in northern Europe :
The Met Office has just released a report entitled “why was the start to spring 2013 so cold?”
The immediate cause was a natural climate fluctuation called the North Atlantic Oscillation (NAO). The NAO switches between two states, and this winter (in its negative phase) saw a southward shift of the jet stream, bringing cold air over the UK from northern Europe and Russia. 
The Met Office identifies three other natural climate variations that may have made the negative NAO phase more likely. 

One is the recent behaviour of another natural climate fluctuation, called the Madden-Julian Oscillation (MJO). It was particularly strong during late February and March – often a sign that a negative NAO is on the way. 
This winter also saw what’s called a Sudden Stratospheric Warming (SSW) event, where winds in the stratosphere above the north pole reverse direction. This brought cold weather conditions to the UK. 
Finally, Europe’s climate is influenced by another natural climate system – the Atlantic Multi-decadal Oscillation (AMO). While the influence on UK winters is unclear, the report suggests: 
“[T]here is some evidence that the changes in Atlantic sea surface temperatures associated with the AMO, dispose the circulation to give drier than normal spring conditions over the UK and northern Europe.” 
Arctic Amplification
What about the effects of human-caused climate change? One question that has been much discussed recently is whether the recent rapid decline in Arctic sea ice could contribute to a change in the UK’s weather.

The new report explains how this could work
“It is argued that amplification of global warming over the Arctic is reducing the equator to pole temperature gradient, thereby weakening the strength of the mid-latitude jet streams.”
This could allow cold Arctic air to push further south, over mid-latitude countries like the UK, and weather patterns could stay longer in one place. 
The possibility of a link between the Arctic and UK weather appears to be gaining scientific support, but the Met Office acknowledges it’s still an “area of ongoing research.” The Met Office has told us it’s holding an “ informal workshop” in the next two to three months for leading UK scientists plus several international experts. 
Multiple factors
While scientists are making progress in working out how climate change could influence the odds of abnormal weather, it would be unwise to attribute one year’s events to a single cause. The report points this out, noting that: 
“…no single explanation can account for the cold conditions observed.” 
The report also highlights that although this spring was unusually cold,” it is not unprecedented or outside the expected natural variability of our climate.” 
Nevertheless, with what the Met Office describes as “particularly heightened interest” in recent weather, getting to grips with how climate change could be affecting things is important. Even if, as the Met Office suggests, the complexities of the UK weather make “communicating the science drivers more complicated and nuanced than some audiences may wish.”

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