The recent cold weather, including snow in May in the northern U.S., may have some thinking that global warming has taken a pause. Maybe climate is changing back. If only that were so. Unfortunately, the heat content of Earth continues to rise unabated, with most of the increase currently going into the oceans rather than the atmosphere.
The U.S. tends to experience cold snaps because the prevailing wind patterns are moving cold air south from northern Canada and the Arctic. It has to do with the Arctic Oscillation, as shown in this image:
Left: Effects of the Positive Phase of the Arctic Oscillation. Right:Effects of the Negative Phase of the Arctic Oscillation. —Credit: J. Wallace, University of Washington.
We have clearly been experiencing the effects of the negative phase lately. The upshot is that, while the US is colder, much of the Arctic is warmer than normal, so it seems cold to us, but the ice cap is still getting more fragile. Both sea ice and the Greenland ice sheet are continuing to lose volume each year.
An interesting event related to this ice loss occurred late last February, as you can see in the following video.
The way the ice breaks up over such a large area is remarkable. You can get an idea of how it happened from this image of the Arctic on February 23. If you look at the area of ocean north of Alaska and western Canada, the Beaufort Sea, you can see that the ice cover is relatively thin, about two meters.
Compare that with the same area last year, in June of 2012. It was later in the year, so there was less ice, nonetheless much of the Beaufort Sea was covered with ice over four meters thick, shown by the orange and red colors.
Currently, Arctic ice volume and extent are running very low for this time of year, slightly lower than last year. It seems likely that we will see another record low ice cover this September. Please, when someone tells you that climate change is bunk because “it’s cold outside,” remind them that the world does not end at the horizon.