Not really, no. Cumsum is a cumulative sum of yearly increment. The rate is in mm/yr, and I am modelling this rate as a quadratic function of temperature. The cumulative sea level rise over many years (in mm, say) is the time-integral of the rate, or cumulate sum. In equations, that means rate = d(slr)/dt and slr = \int_0^t rate(t, T(t)) dt. If the temperature were a linear function of time, the cumulative sea level would become a cubic function of time. Sorry if I take for granted things I have always considered under the same light.
EDIT: I see you are probably an economist and used to relative rates of growth (which accumulate as a product over time). Whereas in climatology when we say sea level rise, or rate of sea level rise, we always talk about arithmetic series.