Four Year Average at new Record Low

In the Arctic, the sea ice volume 4-yr average reached a new record low this week due to climate change. The new milestone was 13.7 thousand km³.

Q: Where’s the data source for this plot?
A: Here: http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/data/
Q: How can anyone make a 4–year average graph?
A: Easy. Use a computer. Add all the ice for the latest 4×365 days, divide by that number of days.
Q: Why would I even do that?
A: Let’s say you want to know how much ice we have in the latest 4–year period compared to the 4–year periods before that.