Sat 30 Nov, 2019 08:07 pm
Hot air rises and cold air sinks, but cold air can only sink because it has risen and then cooled. Otherwise it wouldn't be up there to begin with!
The sun heats the Earth and builds a mountain of air. Greenhouse gases help the air heat up even more and push itself even higher than it would without the greenhouse gases blanketing it.
As the invisible mountain of air builds up, the planet begins tilting away from the sun. The ground below cools, especially in the arctic, so that air condenses down making room above it for more warm air to flow in on top of it.
As the air keeps piling up in the arctic and cooling/condensing, the dense arctic mountain of air builds up so high that the cold air begins sliding back down the mountain into lower latitudes, like an avalanche.
So the cold fronts that bring cold arctic air down to lower latitudes are thus avalanches of cold air from a mountain that was built up as the Earth heated throughout the warmer months of the year, pumping air and water vapor to higher altitudes.
What goes up must bear down; and that's how the greenhouse effect helps energize winter.