Simple Models For Climate Change and Variability by De-Zheng Sun and His Collaborators

As GCMs become increasingly available for small research groups to run, simple models now risk extinction as useful tools for researchers. The popularity of GCMs is driven in part by the natural human tendency to be associated with the more sophisticated and the more complete, and in part by the ever improving readiness of these models as well as the needed computer resources to run these models. The GCMs, usually with a global output on a realistic geographic map also allows more direct comparison with the observations. The general belief that the more is included the better is the model, coupled with the practical demand of regional information for climate change and variability , ensures the superior place of the GCMs in the hierarchy of models in climate change studies.

Yet, simple models have some inherent advantages over the GCMs as their behaviors can be more completely understood. Moreover, some insights can only be obtained by simple models. For example, if we want to know the equilibria of the climate system or one of its subset system, then simple models can give information GCMs cannot give, particularly in the case the equilibria are unstable (and thus cannot be obtained by numerical integration).

Simple models are capable of simulating complex climate behaviors, and are not necessarily inferior to GCMs. One example is one of my own simple model for ENSO (Sun 1997, Liang et al. 2012) which can produce strongly ENSO asymmetry as observed while most coupled GCMs collected in CMIP5 are not able to (Sun and Zhang 2014).

Historically, simple models have apparently played an irreplaceable role in understanding the behavior of the climate system. Notable examples are Manabe's radiative convective model, Hansmann's model for the midlatitude SST variability, Stommel's box model for the variability of the global thermohaline circulation, etc.

In the same spirit of these giants in climate science, I have over the years developed quite a few simple models of my own, which I believe have helped me to understand the behaviors of the climate system better. The following are highlights of of some of these models. numerical codes are available through contacting me at

The Model The EquationsKey Behavior
Publication: Sun, D.-Z. and Z. Liu, 1996 : Dynamic ocean-atmosphere coupling: a thermostat for the tropics. Science, 272, 1148-1150.

The Model The EquationsKey Behavior
Publication: Sun, D.-Z., 1997: El Niño: a coupled response to radiative heating? Geophys. Res. Lett., 24, 2031-2034.