Arctic, Antarctic Ice in Free Fall
November 20, 2016
There are weather and climate records, and then there are truly exceptional events that leave all others in the dust. Such has been the case across Earth’s high latitudes during this last quarter of 2016, on track to be the planet’s warmest year on record. Sea ice extent and area have both plummeted to record lows for this time of year in both the Arctic and Antarctic. Such dramatic losses rarely occur at the same time, which means that the global total of sea ice coverage is phenomenally low for this time of year. The weirdness extends to midlatitudes: North America as well as the Arctic have been bathed in unusual mildness over the last several weeks, while Eurasia deals with a vast zone of above-average snowfall and below-average temperatures. Let’s look at each of these to see what’s up and where they may (or may not) be related.
Round-the-clock darkness usually forces a rapid growth in sea ice across the Arctic by November, but that process has been much slower than normal over the past month or so. There is now far less mid-November sea ice in the Arctic than in any other year since satellite records began in 1979. For the five-day average ending November 17, the difference in Arctic sea ice extent between this year and the next-lowest year (2012) was 582,000 square kilometers, an area about a third larger than California. It’s an especially dramatic example of the long-term decline in sea ice across the Arctic that’s been evident for upwards of 20 years.
A few years ago, a key Climate denial talking point centered around a short-lived high anomaly in Antarctic sea ice. That’s going away now, but here’s the video I made explaining it in the words of major league experts.
Experts agree that the laggard sea ice this month around Antarctica is a separate matter from the Arctic, because sea ice in the northern and southern polar regions is produced by two markedly different circulation regimes and geographies. “At NSIDC, we generally frown on the practice of looking at the global sea ice extent,” said Mark Serreze, director of the National Snow and Ice Data Center, “the reason being that ice in the two hemispheres tends to behave rather differently; while Arctic extent shows clear downward trends in all months, the pattern for the Antarctic has been much more complex.” Serreze and several other ice experts I contacted agreed that there was no obvious explanation for why sea ice extent would suddenly dip in unison in both the Arctic and Antarctic when the two processes are typically so uncorrelated. Previous record-warm years didn’t behave this way. Could some previously dormant or absent connection be popping up just now? If so, it’s not an obvious one. NSIDC’s Ted Scambos: “I’d say that to link the two poles with a single causality chain at the seasonal/annual level is probably about a decade of research in the future.”
Unlike the Arctic, sea ice extent around Antarctica has actually shown a slight increasing trend over the last couple of decades. This might seem odd in a global climate that’s warming, but there are several plausible explanations, as we discussed in an October 26 post. Just two years ago, in September 2014, Antarctic sea ice extent hit the highest values observed at any time of the year since monitoring began in 1979. We’re now seeing the lowest values on record for mid-November, and the margin between this year and all other years has been increasing. For the five-day average ending November 17, the difference in Antarctic sea ice extent between this year and the next-lowest year (1986) was an enormous 1.12 million square kilometers.
An Arctic that’s having trouble cooling down
Temperatures north of 80°N smashed records for warmth throughout the winter of 2015-16. Now they’re on an even more torrid pace. In mid-November, temperatures across the high Arctic spiked to readings more typical of September, about 40°F above average for this time of year (see Figure 3 in our November 17 post). “Continued persistence of this pattern may significantly affect sea ice thickness into 2017,” tweeted Zach Labe (@Zlabe, University of California, Irvine) on Monday.
It’s difficult to measure sea ice thickness and volume in a continuous way, but the University of Washington’s PIOMAS model, which estimates sea ice volume using the available data, dove into record-low territory this month, just weeks after a rapid refreeze took place early in the autumn. “Whatever the respective roles of natural variability and [anthropogenic global warming], these wild swings do not inspire confidence in a semi-stable system,” noted Neven Acropolis in an early-November update on the Arctic Sea Ice Blog.