se tasks would be a lot simpler if we could just
% reshape the data into matrix.  The problem, of course, is those pesky
% leap days, always leading to uneven numbers of datapoints in different
% years and throwing off attempts to reshape.  The |reshapetimeseries|
% function cleans up that messiness:

[ice, yr, tmid] = reshapetimeseries(t, extent_N);

cla;
plot(tmid, ice, 'b')
hold on

%%
% By default, it uses date bins, which makes sure to keep calendar dates
% aligned from one year to the next, and averag