NOAA reports that June, April to June, and the Year-to-Date Global Temperatures are the warmest on Record. Last month’s combined global land and ocean surface temperature made it the warmest June on record and the warmest on record averaged for any April-June and January-June periods.
Arctic sea ice covered was 10.6 percent below the 1979-2000 average extent and the lowest June extent since records began in 1979. This was also the 19th consecutive June with below-average Arctic sea ice extent. But, look – Antarctic sea ice extent in June was 8.3 percent above the 1979-2000 average, which made it the largest June extent on record. How did we get the smallest Arctic and the Largest Antarctic extents records ever?
Climate change of course. As counter-intuitive as it sounds, We have finally locked down one of the main reasons that Antarctica’s sea ice has been growing (see here). There are a number of reasons actually, but the biggest today seems to be the ozone hole. What it is doing is increasing winds in Antarctica and lowering the level of the Stratosphere. this bring the cooler air of upper atmosphere closer to the earth’s surface which allows more mixing and colder temperatures.
But here’s the problem with this theory. Antarctic temperatures have not dropped. They have warmed. Not as much as the world average, or near as much as the Arctic, but they have not dropped. (This diminished warming in the Antarctic is completely supported by the climate models. the ocean around Antarctica moderates its climate and keeps it from warming, whereas the Arctic is surrounds by land, which accelerates warming.) Temperature however is not the only thing that can increase the freezing of sea water. The higher winds increase cooling of the ocean surface. This allows two other things going in the Antarctic to increase the extents of sea ice.
Ice discharge in Antarctica has increased to about the level that we are seeing in Greenland. these extra icebergs melt quickly and decrease the salinity of Antarctic Ocean surface water. Less salinity allows the water to freeze at a higher temperature. (Normal sea water freezes at about 28.4 degrees F.)
The final thing is a feedback effect. More sea ice decrees the amount of mixing of surface waters because once the surface freezes the wind can’t move the water around, which is responsible for mixing the less salty water at the surface with the more salty water below. So the lack of mixing keeps the surface waters less salty, allow freezing to occur at a higher temperature. (see here)