The true is that the form in which the leap years are manage will always be problematic, so it is just knowing the form in which the sources manage the leap years, to clearly understand their graphs.
There are other things that concern me more. After the huge melt that ASI had on September 2007, the Director of NSIDC Mark Serreze gave a conference at the American Geophysical Union (AGU). He recognized that he was expecting an
ice-free Arctic by 2030. He said that the melt will accelerate and he talked about the possibility that 2007 was the year of the tipping point.
We have a new impressive record at 2012.
We also have two years similar to 2007: 2011 and 2015. So, why the NSIDC show a linear trend, like if we have 40 or 50 years more? If scientific people of NSIDC expressed their concern of IPCC models at 2006, before the melt of 2007, why they have say nothing on the new IPCC models? Why we have a new definition of
ice-free Arctic, in which we need 5 consecutive years of SIE under 1 million km2 to consider that the world is experience a
ice-free Arctic? Why humanity keeps talking about
extent, when we should agree that what matters is volume and the tendency of volume is an immediate colapse?
So, the big proportion of the humans will be surprise, when the governments
will make official that Climate Change is not going to melt the Arctic Sea Ice at 2100, but in 1 to 10 years.
I understand your point about the equinoxes and solstices, but what I think is that as community, it is more important that we push to make everybody understand that the Arctic Sea Ice has less than 10 years to disappear.
2007 Mark Serreze conference at AGU:
http://www.agu.org/webcast/fm07/Serreze/index.htmlEdit: Pardon my English

Corrections and addendums in Italic.