Increase/increment and decrease/decrement

Question

I know that there are differences between increase and increment and decrease and decrement in general. E.g. increase/decrease can be used as verbs whereas increment/decrement cannot, and increment may not necessarily imply an increase in some contexts (Mathematics).

However, I am not aware of any differences in meaning between them when used as a noun in a context similar to this:

The expected increase in global temperatures vs. The expected increment in global temperature

I checked the usage in the English corpus with Google Ngram Viewer and the pair increase/decrease seem to be used more frequently.

Is there a subtle difference in meaning between these two? Would there be a subtle difference, if I used decrease and decrement in the previous comparison?

Answer 1

increase noun A rise in the size, amount, or degree of something. ‘some increase in inflation is expected’ - lexico

increment noun 1 An increase or addition, especially one of a series on a fixed scale. ‘all sizes from 4–30 mm in 1 mm increments’ - lexico

Increase is more generic, referring to the direction of change. Increment is a kind of increase, but it pulls in the notion of steps or quanta.

An increase in global temperatures refers simply to temperatures increasing, by any amount. Global temperature increments, however, brings in the connotation of some quantum, say half a degree. One can speak of temperatures increasing by two increments, for example.

So the two terms are closely related, but not fully interchangeable. Likewise for decrease vs decrement.

Answer 2

This answer follows on from that of Lawrence, to deal with the non-mathematical use of increment.

In the U.K. , it is common to pay certain professionals, especially in public service, on an incremental basis. Teachers, nurses, police officers and other public service workers are paid on an annually increasing scale up to some maximum. This is (or was) designed to reflect the rising value of an employee with increasing experience. So my own salary as a public sector employee rose from £13,000 to £21,000 in annual increments over about six or seven years and then rose only by a. annual inflation-based increase. I know of no such equivalent decrement!

In recent times this idea of a novice taking time to reach the full rate for the job has been ignored by politicians of the right, who regard them as simply ‘automatic pay rises’, unjustified by performance. it at the moment a kind of compromise exist, whereby the scales remain but with ‘efficiency thresholds’ at certain stages.