SANDY has been churning up the Atlantic since last week and just now, as I write, has shrouded my home in the drab darkness of a greater Washington afternoon without electricity.

An Arctic jet stream pushing down from Canada and Greenland and a low-pressure winter system moving in from the west are combining to block what ordinarily would be Sandy's course — which would be to head towards the mid-Atlantic US coast and then to head back out to sea, following the warmth of the Gulf Stream.

Instead, it's going to New York, crossing the coast near where New Jersey meets Delaware, and then on to Maine in the north and north-west towards the Great Lakes.

And because of that blocking effect, Sandy will be dawdling through the north-east, it's effects lingering for as much as 36 hours in most of the areas it hits.

Sandy has an unusual pedigree. Most hurricanes draw their power from warm seas. But while Sandy's genesis was a tropical wave in the west of the Caribbean on October 22, it has evolved into what the experts call an "extratropical" storm, one that is gassed up by atmospheric contrasts.

Even before landfall, Sandy was smashing records — it had overtaken Lili (1996) as the biggest Atlantic storm in 24 years of record-keeping, its tropical-storm-force winds reached to more than 800 kilometres from the centre; its hurricane winds were stretching 280 kilometres from the centre.

That ridge of high pressure pushing down from Canada and Greenland, a blocking high as it is called in the trade, has an intensity that intrigues meteorologists because, they suspect, it is caused by the reduced sea ice in the Arctic — all a part of climate change.

As reported on Climate Central: "The 2012 sea ice melt season, which ended just a month ago, was extreme, with sea ice extent, volume and other measures all hitting record lows."

And why does this make a difference? "The loss of sea ice opens large expanses of open water, which then absorbs more of the incoming solar radiation and adds heat and moisture to the atmosphere, thereby helping to alter weather patterns."