1. Climate Models Current News and Weather
General Circulation Models (GCMs)
Changes in GCMs since 1970s
How do We Know GCMs are Reliable?
Limitations of GCMs
For Next Class: Read Ch. 12 (pp )

2. https://www. washingtonpost

6. General Circulation Models
Mathematical representations of the climate system, expressed as computer codes and run on powerful computers
Operate in 3-D and have capacity to represent spatial distribution of land, water, ice, elevation of mountains, vertical distribution of greenhouse gases, and changes in solar radiation
Operation of GCMs incorporates physical laws and equations that govern the circulation of Earth’s atmosphere

7. General Circulation Model
Figure

12. Huge improvements
in model resolution
since FAR!

13. . . . and in modeling
the physical
processes!

14. How Reliable are GCMs?
“One source of confidence comes from the fact that model fundamentals are based on established physical laws . . .
Second source of confidence comes from the ability of models to simulate (more or less!) important aspects of the current climate” (IPCC AR4)

15. Orange = Individual Models
Red = Ensemble Mean
Orange = Individual Models
Black = Observations

16. Any Concerns about Models?

17. Limitations of GCMs
We have imperfect observations that provide initial boundary conditions for models.
A model is a hypothesis about how the climate system operates!
Only the dynamic core of the models represent basic physics. All other components of these models are parameterizations, which means they are not fundamental physics but engineering code with tunable parameters.
From Pielke (2011)

18. It is very difficult to accurately parameterize clouds and
cloud microphysical processes in weather or climate models!