Fact of the matter is, the GP is right. Can we at least agree the color scheme could have been chosen better ?
You are also obviously showing a bias towards one conclusion, and accusing opposition to this conclusion of being "plain dishonest" is not constructive. This is data interpretation. Even attributing 100% to your prior (ie. ignoring the data) is not considered dishonest.
Furthermore, when push comes to shove, let me just say that as someone holding a masters in statistics, there is zero useful data on that chart. I think the the point is to show that we are more than 2 standard deviations from the norm ... And then we have a long list of issues with that conslusion. In increasing importance :
1) there is an obvious reason to pick the start of the time series, and that reason is NOT independent of the conclusion that is reached here. Needless to say, that is a huge no-no.
2) more generally the data supporting the conclusion is not randomly drawn from the distribution. Again, huge no-no.
3) is the relation between time of year and sea ice extent well established ? For instance, does the minimum drift ? How much ? (Why I pick that one: because if you ignore the time of year, flatten the data, we are suddenly very far removed from a 2 sigma deviation, and arrive at a much more sane conclusion : lowest extent ever, but not hugely different from before. And of course, seeing 2 extremes of a slowly evolving variable close together is not exactly strange. When you're climbing the hill, every step sets a "new height record". Focusing on that is misleading, to say the least).
How often do we hit "lowest ever" because the minimum extent falls at a slightly different point every year ? (looking at the data: quite often, for instance, we hit lowest ever and highest ever extents last year. Lines that hit "lowest ever" at some point: dark red, dirty green, thick bright green, thin dark green, thin light green, purple, orange and another medium-dark green. I can't be bothered to look up the years, but I think the point stands: lowest ever is not a rare occurrence, and therefore "more than 2 sigma below the norm" is not an accurate way to report that).
You are making assumptions just by choosing which 2 variables to graph against eachother. Are these assumptions valid ? Why ? If you don't have a reason, then please, shut up until you've done your homework.
It may make a lot more sense to plot the minima at the same points every year, to prevent normal noise from generating these extremes, or just only compare minima and maxima, and even then, smoothing out over 4-5 years seems necessary. Or perhaps just don't report things like this.
3) more fundamentally, why would the data be normally distributed at all ? This seems to me unlikely in the extreme.
Technically speaking, the data is contradictory: it leads to a conclusion that disproves itself. The steps work like this : if the sea ice extent is indeed dropping over time (the conclusion of the graph), then obviously it's distribution over time cannot be normally distributed. Unfortunately that is a necessary precondition for interpreting the data in the first place. If the data is not normally distributed, then there is nothing strange about a 2 sigma deviation, which at that point is nothing but an arbitrary numerical value that has nothing to do with the distribution.
If you want to prove that the data is indeed less than the data of the previous years, there's tests for that. This is not it.
4) that grey band obviously covers 98% of the data in the way years are reported here. Years are reported as special, when the 2-sigma deviation is based on days. The time series regularly dive outside of that band, and it's easy to see why: over (2016-1978)*365 days, we should expect ~2% 2-sigma events (days). That's a LOT of days.
5) we should keep our heads screwed on and ask ourselves if the data is really showing what we think it's showing. I would argue no. It looks to me like something prevented sea ice from reforming between August and December of last year. It seems to me unlikely in the extreme that such a sudden and big change would result from the minute temperature change that global warming contributed this year. Maybe not entirely out of the question, but that's an extraordinary claim, requiring extraordinary evidence. And frankly, this article is not off to a good start.
Or to put it more technically : it looks 2016 is drawn from a different distribution than the other years. That means you should find out what happened using other means, and stop using statistics. It cannot help you in this case.
Conclusion: there is something weird happening, true, but based on intuition alone. And let's be honest : chances are very good it's not global warming. Something changed, and it was not a 0.2 degree temperature change. This is way too big for that to be a valid explanation.