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In a complex tango between ocean and atmosphere, warming is causing icy polar air to be displaced southwards. "The linkage is becoming clearer and clearer," said Dim Coumou of the Potsdam Institute for Climate Impact Research (PIK) near Berlin.

The theory derives from a long-studied Arctic phenomenon called a positive feedback—-in plain words, a vicious circle.

Rising temperatures are melting the Arctic's floating cap of sea ice, especially in summer.

Take away reflective ice, and you have a dark sea that absorbs solar radiation, which in turn reinforces the melting, and so on.

But the theory suggests the added heat, stored over a vast area of surface water, is also gradually released into the atmosphere during the Arctic autumn.

It increases air pressure and moisture in the Arctic, reducing the temperature differential with lower latitudes.

Here's what happens next: The polar vortex, a powerful circular wind that essentially pens Arctic air to the roof of the world, begins to weaken.

Finding itself released, a mass of moist cold air spills southward, bringing snow and chill down into North America and Europe.

And it tends to stay there, because of what happens to the jet stream.

Instead of encircling the northern hemisphere in a sturdy and predictable fashion, this high-altitude wind takes a lazy looping path, zigzagging over the United States, the Atlantic and Europe. The southern parts of the loops get a bout of cold weather that becomes stalled in place.

"Heat that is stored in the (Arctic) ocean can rapidly transfer to the atmosphere, and this affects the dynamics" of northern hemisphere weather patterns, said Coumou in a phone interview.

"We've had a couple of winters (in Europe) where you've had rather shorter-term cold spells, of a duration of maybe 10, 20, 30 days... It's been the same in the continental US and Canada where they've seen similar quite bizarre cold spells but of a relatively shorter period."

"With the changes in sea ice, we set up a situation where we stack the deck, increasing the probability of these invasions of cold Arctic air," Charles Greene, director of the Ocean Resources and Ecosystems Program at Cornell University in New York, said. More at http://phys.org/news/2013-03-global-harsher-winters.html]

There's a lovely graphic at http://www.scribd.com/doc/72047560/Potsdam-Graphic-646254a] which will help explain it to you, if you can wrap your head around a visual. Not that you'd ever be caught DEAD even looking at it, we know.

Then there's

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Cold Snaps and Global Warming Go Hand In Hand

Frigid temperatures like these are sometimes used to refute the idea that the planet as a whole is getting warmer with each passing year. That's just not so.

....phenomenon known as Arctic Oscillation, a phrase used to describe the interaction of the jet stream and Arctic air during the winter. It can cause unseasonably cold air masses to sweep over what are normally temperate latitudes, NASA reports, making for unusually cold and severe winter weather across many parts of the U.S.

This bitterly cold air even can make it too cold to snow across regions of the country that normally see double-digit snowfall amounts each year, the Guardian newspaper of London reported last week. Because colder air has a lower capacity for holding water than warmer air, it can be more difficult for snow to form when temperatures reach the teens and single digits. More at http://www.weather.com/news/weather-winter/nasa-cold-snaps-global-warm
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We just had that:

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It's freaking freezing from the Great Plains to the east coast. There are far too many cities with wind chills below 0F to count. On Wednesday, the high temperature in New York City failed to climb above 20F for the first time in three years, after weeks of above-normal temperatures. Interestingly, there is little snow accompanying the cold.

While the east is a tundra, Denver, Colorado is dealing with near-record highs with temperatures in the 60s. When we expand our look to over the past month, record high maximums and minimums are running 2 to 1 ahead of record low maximums and minimums in the United States. The United States' average temperature in 2012 was 55.3F – 3.2F above the 20th-century average and 1F above the previous record, 1998. When you drill down to specific locations, there were 356 record-high maximum temperatures compared with only 22 low maximums – a 16 to 1 ratio – over the past year. There were 105 record-high minimum temperatures against only 4 low minimums – a 26 to 1 ratio.

You'll note I didn't mention anything about snow in describing the extreme conditions. Citing snow statistics to try to relate the relative cold and warmth is simple for us to do because it's easy to link white ground to cold air. What you should recognize is that snowfall coverage can vary from week to week and year to year, and it's not necessarily correlated with temperature.

Consider this season's snowfall. Only about 40% of the United States is covered by snow in the heart of winter. The major cities along the east coast are especially in a major snow draught. Boston only received 9in last winter and only a little greater than 7in so far this year against a seasonal average of 44in. New York got only 7in last year and is only up to 5 inches right now, which is far below the average snowfall of about 28in. Washington DC had only 2in in the 2011-2012 winter and so far is only at about an inch for the year, versus the long term average of about 17 inches.

Yet, it was just a few weeks ago 67% of country was covered with snowfall. It was also just few years ago that the east coast was flushed with snow. Boston had above average snowfall for three out of four seasons prior to the last two. New York was 20in above average the last two seasons before the past two years. Meanwhile, Washington had its snowiest season just three years ago.

Certainly it is difficult to have a snowy season when winter temperatures are the second warmest on record, as they were for New York last year. Still, the relationship between cold and snow is not as compact as you'd like to believe. Many parts of the world, especially the poles, actually get less snow when temperatures are below average. Even much of Canada tends to get less snow when the temperature drops. Meanwhile, places further to the south like the Southern United States tend to get more snow when temperatures are below normal.

Why the difference? Colder air has a lower capacity for holding water than warmer air. It's not that it can't snow at 20F, 10F or even 0F. It's just that it's more difficult as the upper atmosphere becomes colder. In a city like Minneapolis where the average January high temperature is 24F, you'd rather have a temperature that is normal to slightly above normal for a good snowfall. In New York where the average January high is 38F and low is 27F, you want either somewhat below to normal temperatures for snow depending on the time of day. In Atlanta, on the other hand, where the average January high is 54F, you want temperatures well below normal, or it will rain.

Another important point is that you can have a well above winter temperature wise and still make out with plenty of snow. The best example that comes to my mind is 2005-2006 winter in New York City. The mean temperature for the winter was 3F above normal or about warmer than three-quarters of the winters. Despite that, New York got 40in of snow including the largest snowstorm on record – of 26.9in in February of that year. More at http://www.guardian.co.uk/weather/2013/jan/24/big-chill-cold-snow]

If all of that is too simple for those who are even willing to read anything, try this:

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We want a clear answer.

Is manmade global warming responsible for the surge in severe heat events we’re seeing in recent years around the globe?

The world’s climate scientists have a clear answer:

Yes. It is.

“It’s about as solid as science ever gets,” climatologist James Hansen tells ABC News.

To cut through the fog, here are four different quick and fun explanations, all scientist-approved.

Middle schoolers understand them in a flash. It’s like duh.

You can too. One is even a little animated cartoon.

1 A Pot of Cool Water in Your Mind

Take — or imagine — a round pot of cool water.

Put it on a gas stove with the flame on very low.

Soon, a few little bubbles will occasionally rise to the surface.

Imagine a tiny circle at the exact center of the surface of the water.

Now, turn up the flame just a little more — but not completely.

You’ll notice there are a few more little bubbles; they’re rising more frequently.

Wait until one of those bubbles happens to burst inside the tiny circle.

Can you say whether that bubble was “caused” by your turning up the heat?

No. Of course not. There were bubbles before you turned up the heat, and some might have burst in exactly the same place.

Could you have predicted precisely when a bubble would burst inside the tiny circle?

No. But you knew that there would be more bubbles more frequently.

That’s like manmade global warming, as described by the world’s scientists — with each bubble like a single extreme heat-related weather event.

The few little bubbles before you turned up the heat were like the occasional extreme weather events before the year 1800. That’s when the Industrial Revolution began and then started heating the atmosphere by pouring heat-trapping CO2 into the atmosphere by burning coal and other fossil fuels, and by other industrial-scale activities including clearing of forests, which also release large amounts of CO2.

Before 1800, extreme heat-related weather events — like the bubbles before you turned up the heat — were far less common than now.

And as industrial humanity heated up the air with more greenhouse gases, the extreme heat-related weather events became more frequent.

But it doesn’t make any sense to say any one bubble “was caused by” turning up the gas.

This simple “Parable of the Pot” avoids what is called “the single cause fallacy.”

Scientists will not say any one event “was because of global warming,” not exactly, because it could sound like it’s stating a single cause, which never exists, though sometimes scientists do take the time to execute complicated calculations to estimate the degree to which manmade global warming had increased the probability that a known single extreme event, that did happen, would have happened…

(Though this too can be a little confusing, since the event certainly did happen — is now known with 100 percent certainty to have happened.)

In fact,scientists say, even when the planet is much hotter than today (if we don’t manage to reduce manmade global warming but go on with business as usual) it will still not be possible, then or ever, to say that any one extreme weather event was, in a literal sense, solely “because of” manmade global warming.

This metaphor of the pot of water can go a little further: you may also notice that as you turn up the heat, there start to be some larger bubbles. And that if you turn the flame up to full, it will be bubbling a lot — “a rolling boil.”

That is similar to what climate scientists tell us is coming — with first signs already here — if humanity doesn’t somehow “avoid the worst impacts of manmade global warming.” And those far bigger bubbles (which you don’t see when the flame is only extremely low, on “simmer”) will, in a narrow sense, be “because” humanity turned up the heat.

2 A Naughty Baseball Player (Animated)

There is a brief animated cartoon that explains it a different way:

You can also check out the site’s simple explanations of how global warming affects different specific kinds of extreme weather — in the node on the right of the cartoon that says “Torrents, Drought & Twisters — Oh my” — at “Steroids, Baseball and Climate Change" ( https://www2.ucar.edu/atmosnews/attribution/steroids-baseball-climate-
change])

3 Two Giant Dice (One of Them Loaded)

- A 2012 video repeating what Congress learned in 1988

Or, how about a short 2012 video with a pair of giant dice, one of them loaded.

James Hansen’s Giant Dice for Congress in 1988

In 1988, climatologist James Hansen, director of NASA’s Goddard Institute for Space Studies, testified to Congress that manmade global warming had “already started” warming the climate, and was, he said, “loading the dice” for extreme weather events to happen ever more frequently.

While in Washington for that testimony, he went over to our ABC News Washington Bureau to appear on “This Week With David Brinkley,” alongside fellow scientist Michael Oppenheimer (both in the above picture) who had testified on the same panel with Hansen about the great dangers of global warming.

Hansen prepared two giant dice.

One had two sides painted white (normal temperatures), two blue (cooler than average), and two red (hotter than average.)

The other was “loaded” to make hot turn up twice as often — four sides painted red, not two.

Hansen did this, he now tells ABC News, to clarify the confusion created by the sloppy reporting in the media about what he was trying to get across.

Hansen tells ABC News that the members of Congress questioning him seemed to understand very well what he was saying and predicting.

Hansen even got the rate of warming about right: within 20 years, the number of unusually hot days had about doubled, from one-third to two-thirds.

But let Hansen himself explain it to you now, again — with the same well-saved dice still in his hands.

(He told this reporter he keeps them on a shelf in his office.)

Here’s a video of a recent (April 2012) interview with Hansen about these dice, and related matters.

Just scroll down an inch to the frame showing an older Hansen — 24 years after the above 1988 photo — his predictions now proven accurate.

This interview is conducted by the New York Times’ Andrew Revkin who has been covering global warming for decades, and is posted on his nytimes.com blog, “Dot Earth.”

Hansen tells ABC News that lately he’s been adding a new element to his demo with dice: he’s made one side brown to represent the more extremely hot seasons the world has been seeing.

4 A Really Simple Graph (Time Tested)

Spend 20 seconds with this simple graph.

It shows that if there were no excess greenhouse gas emissions (from burning coal for electricity, cutting down forests, etc.) then the world’s average temperature would not be rising steadily… but instead, it would have remained level over the past century, or even slightly cooled.

Computers ancient by today’s standards produced this result decades ago at labs around the world.

And they still do, using many different mathematical models and vastly more powerful computers.


If There Had Been No Excess Manmade Greenhouse Emissions…

Note that going left to right covers the years from 1900 to 2000.

The black “observed” line is what the world’s thermometers showed actually happened to the world’s average temperature from 1900 to 2000.

The Pink bar, “with human effects,” shows what computer models say would happen to the world’s average temperature during that time — when the scientists enter all their data before the year 1900 and then stand back and see if the computer reproduces what did actually happen, which they continue to do with increasing and extraordinary accuracy.

The blue bar — “natural forces only” — shows what computer models say would have happened if the human warming forces — excess greenhouse emissions from burning coal, cutting forests, etc. — are removed from the data put into the computers for before 1900, leaving only natural causes to run through the years 1900 to 2000.

Actually, this shows how it is therefore even logical to say — in this one narrow sense — that the current global warming “is because of” humanity’s excess greenhouse emissions and other warming activity (taken all together as a single “triggering cause” working in concert with other conditions), since this graph shows that you can say that “if there were no excess greenhouse emissions, then we wouldn’t have this recent warming.”

–The warming which countless scientific studies of many different types in many different countries in labs and universities around the world have linked directly to manmade global warming – shown it to be a “necessary condition” or “triggering cause” for the increased frequency – repeat, frequency – and sometimes far greater intensity – of the heat waves, drought and flood we’ve been seeing lately…

…and which the world’s climate scientists say will not only continue but quickly worsen until and unless humanity somehow deals with the crisis (which is already a cause of great loss and suffering around the world) and drastically reduces its greenhouse emissions.

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A few Extra One Liners… all scientist-approved:

•Even a hundred years from now, if humanity has failed to stop manmade global warming and it is far hotter on the planet with far less snow or ice, similar to the days of the dinosaurs 65 million years ago, it will still be the case that you could not say any one weather event is being “caused by” global warming… because that would be to fall, again, into the trap of the single cause fallacy.

•Journalists — and anyone talking about all this — can easily avoid the problem by simply saying something like: “This exactly fits the pattern long predicted of increasingly frequent severe weather events.”

•Of course there have always been extreme heat waves, drought and flood – going back Billions of years, but it’s just that manmade global warming is now shown by virtually all the world’s professional climate scientists to be causing them to be much more frequent, and in some cases (such as intense downpours, intense snowfalls, the extension and height of heat waves) to be more severe more frequently.

•Even when scientists do complicated calculations to estimate the degree to which manmade global warming made any one heat event more likely, it is still just an estimate of probability, however horrendous the odds may be (– As many now are — for example, as one report says, “la Nina-related heat waves, like that experienced in Texas in 2011, are now 20 times more likely to occur … than (in) La Nina years fifty year ago.”) http://abcnews.go.com/blogs/technology/2012/07/its-simple-global-warmi
ng-is-causing-the-extreme-weather/

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Would be neat if any of you guys would actually try to REFUTE the above, but of course we know you won't. You'll just keep on putting up ridiculous observations of any cold weather and say it "refutes" climate change. But it only took a few minutes, and one of the intelligent among us might find something in there interesting, so no skin off my nose.