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The scientists said there was no evidence that the weather changes were a result of man-made climate change. - DB2

I'm not gonna place too much stock in a news reporter's summary of current scientific thinking. What appears to be happening doesn't lend itself well to simple summarization.

Here's a well-produced video from the Yale Climate Forum on the subject of "global weirding" in the northern hemisphere:

The video explains the interactions between a warmer Arctic and the jet stream, as influenced by the Arctic Oscillation. Toss in increased water vapor and you can begin to understand what's happening.

For those too busy to spend 11 minutes to view the video, I'll summarize it thus:

A warmer Arctic decreases the temperature differential between polar latitudes and the mid-latitudes. This decrease in temperature differential weakens the jet stream. The Arctic Oscillation is then amplified due to a weaker jet stream. As a consequence, the jet stream meanders in ever greater amplitude resulting in greater weather extremes of longer duration in the mid-latitudes.

One can see that a number of factors are in interplay. One cannot simply say: "It's all due to AGW." On the other hand, one cannot adequately understand observed weather extremes without considering the effect of a warmer Arctic.

Here's a Cornell University article that also explains what's happening in greater detail:

The dramatic melt-off of Arctic sea ice due to climate change is hitting closer to home than millions of Americans might think. That's because melting Arctic sea ice can trigger a domino effect leading to increased odds of severe winter weather outbreaks in the Northern Hemisphere's middle latitudes...

A warmer Earth increases the melting of sea ice during summer, exposing more dark ocean water to incoming sunlight. This causes increased absorption of solar radiation and excess summertime heating of the ocean -- further accelerating the ice melt. The excess heat is released to the atmosphere, especially during the autumn, decreasing the temperature and atmospheric pressure gradients between the Arctic and middle latitudes.

A diminished latitudinal pressure gradient is linked to a weakening of the winds associated with the polar vortex and jet stream. Since the polar vortex normally retains the cold Arctic air masses up above the Arctic Circle, its weakening allows the cold air to invade lower latitudes.

Granted, one has to actually THINK about all this but, really, the logic is inescapable.
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