Initial Conditions and Quantifying Model Climates: Does it Matter Where We Come From?

Abstract

There does not exist an agreed-upon procedure to quantify model climates from their output. Here, we explore differences in characterisations of regional variable climatologies arising from the application of three climate quantification approaches to the output of an initial condition ensemble climate system model experiment. We find that that ensemble member trajectories, distinguished in set-up only by the round-off order differences in initial atmospheric temperature, can—over certain regional domains and for particular initial system states—produce significantly (\(p\ll 0.01\)) different variable probability distributions. In addition, using different quantification approaches to capture what might be presumed to be the same “climatic state”—which itself may be influenced by the initial climate system state—can yield significantly different distributions. We conclude that a multivariate distribution, sampled over both time and multiple ensemble members, together with measures of autocorrelation, may serve as a useful quantification approach for model climates.