[CF-metadata] change_in

[Jonathan Gregory]

Dear Bryan

I see what you mean about the possibly ambiguity of "change" applying to
other coordinates than time. I can't think of a single word which would do
the job, but we could use the phrase change_over_time_in. Would that be
all right and not too cumbersome, do you think? It seems logical to me to
use the standard name to indicate this, because of the close parallel with
tendency_of, as Karl also pointed out.

cell_methods are for describing how variation within a cell is described
statistically; difference between end and start isn't really a statistical
operation. In general we use systematic parts of the standard name itself
for describing operations which create new quantities such as derivative,
integral, pdf, divergence, product, ratio.

Best wishes

Jonathan