First, almost any question about weather is sailing related.
As TomY said, don't confuse daily weather variations with climate change. This past January there were days I was walking around in a T-shirt and 2 weeks when it seldom got above 5* F. That's weather.
In the poles there is a feedback loop. There is (was) a seasonal pattern in the arctic where ice melts every summer around August to September and then refreezes over the winter. The ice does a couple of things, first it reflects more sunlight than water or land and it has a chilling effect on local atmosphere. In spring, if you go to a ski area that is still open, the parking lot may be 10 or more degrees warmer than the slopes, that's because of the snow on the slope.
As the global atmosphere warms, a little more ice melts in the arctic than refreezes over the winter, at first it was probably imperceptible. Gradually the amount of ice declines exposing more water and land that warms up a few degrees, that causes more ice to melt exposing more land and water. Because the land and water is a little warmer, it takes longer to refreeze in the fall and winter and a little less ice is formed. It may not be readily apparent in the area of snow or ice cover, however, the depth of the ice or snow cover will be less. Less ice in the winter, quicker and more extensive melting in the summer and around we go in an ever increasing spiral of warming temperatures and reduced ice cover.
The other aspect of warming is increased temperature differentials, with more energy in the atomosphere (temperature is essentially a measure of the energy) the energy is discharged through storms with increasing intensity. Storm systems are the way energy is dissipated. A close analogy are on-shore and off-shore winds. As sailors we know that on hot sunny days we can get strong onshore breezes in the afternoon, however, on cool cloudy days the breeze won't fill in. The same happens on a global scale.
Nice explanation, I don't totally agree, but thank you. My problem is that over the years we here in Jersey have lost our beautiful Spring season. We have a much shorter Summer. Winter just seems to linger way to long. Just my take on the subject. (I hate winter, have hade enough cold in my life. Will be spending more time in Sanibel and Pine Island.)
Let's take a look at SailNoProblem's example. Assume that the average winter temperature in Alaska has been -10 for years and that the average rise in temperature from January to July is 40 degrees. Back in the old days the average July temperature would only be 30 degrees, still below freezing and any thawing would be the result of solar radiation. Now move forward a few years, where the average January temperature is now -7 degrees, with a 30 degree rise in temperature, the July temp is now 33 degrees and ice melt is occurring because of solar radiation and air temperature, more ice will melt, there will be less ice the following winter and temperatures will warm faster the following year.
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