Wayne, thanks for that analysis. Sea surface temperatures loom large right now.

Jai, Just a hunch, I think August-September temperature might have minimal impact on ice 2 meters thick or thicker. As ice trends thinner the weather at the end of the melt season could have a greater impact on extent. This might explain a correlation emerging in recent years.

I remember getting the impression in July 2012 that the weather no longer mattered to ice melt (and writing about that thought at the time). For months the extent graphs did not seem to respond to changes in the weather. Perhaps, though, it was just that the location and movement of small low pressure systems did not matter. The lesson from June and July 2013, I thought (by August of that year), was that cloud cover does still matter, if there is enough of it. I still believe there must be ways of improving two- and three-month predictions of sea ice without predicting the weather.

sofouuk, To say the point in a more practical sense, the reason Greenland ice is able to stay solid is because of the dynamics of heat transfers, and not because the magnitude of energy in the environment is too small to produce melting. Things like albedo, air temperature, and cloud cover have to be taken into account to determine the speed of melting.

250 W/m^2 is a rule-of-thumb value for average insolation, which takes into account the fact that the sun is not visible at all times and is at different angles at different times and places. If the sun shines directly overhead at a particular moment, that’s peak insolation, and the rule-of-thumb value for that is 1000 W/m^2. So based on that, the Greenland ice sheet could melt away from sun alone, in not much longer than a century. The reason it doesn’t melt so fast is that it is losing heat to its surroundings.

“[A]bout .02 inches of the 3.3 inches per year global average sea level rise” appears to be an error at Mashable. Based on other sources, I believe .02 inches of 3.3 millimeters per year is what is intended.

Thanks for the Svalbard animation, Wipneus and Neven. It is quite stunning to see.

This is a nice analysis, and I hope readers can take a few minutes to look over it closely, including the tables of coefficients. If “chaotic behavior” is hard to visualize, another way of picturing the change is that Arctic sea ice has become more like a pawn, at the mercy of larger forces at work. That is just a metaphor, of course, but in physical terms, it makes sense that as ice gets smaller and weaker, it is more easily pushed around.

Tim, a curve is more flexible, so it fits more closely than a straight line, and as a result it shows a smaller (narrower) standard deviation. And, thanks for the correction on the Greek letter name. I don't know how I made that mistake.

“STD” has been used as an abbreviation for standard deviation since at least the 1960s, so it is older than the other meaning mentioned above and I would expect all statisticians to recognize it. On the other hand, for someone like me who works with statistics, you could write σ (omega) for standard deviation and I would understand it without stopping to think. But for the sake of the many readers who may not be well versed in such technical matters, especially this year, it might be worth the trouble to spell out things like standard deviation. In that spirit, and for the benefit of those who may be scratching their heads, let me try to explain the significance of this statistic in a paragraph. We’re looking at this statistic mainly to answer the question, is the Arctic sea ice in a steady decline, or is the decline accelerating? 1 standard deviation means that the current level is not so far removed from what you would expect, based in this case on the long term declining trend. So the current reading is consistent with the idea of a steady decline in Arctic sea ice. When we go past about 2 standard deviations, as has happened in each of the past three years, that is not so consistent with the expectation of a steady decline — the decline may, instead, be accelerating.

Looking at the animations from A-Team, I am drawn to the line between Svalbard and the North Pole. If I am reading this correctly, through 2012 this area had a coherent body of multi-year ice that seemed to slow down ice transport toward Fram Strait. This year, by contrast, it looks almost like pouring water out of a bucket.

I wonder if the rapid cracking is an indication not merely of thin ice, but also of bottom melt. I picture bottom melt over time making the ice bottom more smooth so that the ice is more easily blown around by the wind. An object drags less in the water if it is smoother, and then it can go faster, or at least I have heard this is a principle in designing boats and surfboards. If the ice moves faster in the water it seems to me that makes more energy available to propagate a crack in the ice.

Four years ago, before I started the book that I recently finished, I was considering dozens of possible projects, and to choose one, I asked myself, "What could I do that would make the biggest difference for the most people?" The answer was the book I ended up writing. It's easy to imagine how I could take that moment and present it as a profound transformative experience, but the truth is, I was just asking a routine marketing question as part of a management exercise. I think people embellish stories like these mainly because, whatever you accomplish, the public isn't ready to hear, "It was just the result of years of hard work." They insist that the explanation has to be something more dramatic.

So economists harm American politicians by making their eyes glaze over? It's no wonder Hillary was in such an unforgiving mood when the subject turned to economists.