Increase/increment and decrease/decrement

Solution 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.