During our mini heat wave of July 16-19, the Northern Hemisphere reached its warmest day of the year, by one measure, on July 17.
On that day, at about 1 mile above sea level, it was warmer than 23 degrees everywhere in the hemisphere. Just a day or two later, the buildup of cold air at that elevation in the atmosphere began again for the coming winter season.
Nearly coinciding with this peak of summer was the rather frightening development of a meltwater lake at the North Pole. The lake started forming about July 13 as a result of two weeks of unusually warm weather near the pole.
In fact, temperatures were 2 to 5 degrees warmer than average in early July over much of the Arctic Ocean.
Such meltwater ponds develop more easily on thin, young ice, which is now the general condition over much of the Arctic. More solar radiation energy is absorbed by a puddle than by ice or snow, so the more ponds that develop, the faster ice will melt in the Arctic.
In addition to the warm weather, an unusually strong cyclone just visited the North Pole region, bringing strong winds that further help to break up the thin ice. That storm was connected to the cold air that chilled us on the weekend of July 27-28.
The interaction of the warmth, which comes in some degree every July to the high Arctic, and the strong winds associated with this storm can leave the sea ice in a weakened state at the end of this summer.
That will mean that the coming winter freeze will have a harder time creating thick sea ice and the next summer will further erode it in similar fashion.
In this way, warming at very high latitudes is enhanced as the planet warms in the face of increased greenhouse gases.