I went through the technical guide for a modern climate model and counted the user-specified parameters:

1,737 (and I know I missed some).

If you've ever wondered what dials must be set to run a GCM, here they are...🧵
I have been told 'these just physics simulators' suggesting that after entering π, σ, 𝑔, etc and some earth-specific information, the rest is simply the consequence of laws of nature. I would observe this is not entirely the case.
First, the model needs 207 plant optical properties specifying the IR/vis reflectance and absorbance of leaves and stems
Dry and saturated soil/snow albedo
207 + 96 = 303
Beam weights for six spectral bands
303 + 10 = 313
Albedos for various types of dirty ice
313 + 50 = 363
More dirty ice optical parameters
363 + 50 = 413
Last set of dirty ice optical parameters
413 + 50 = 463
Growth/shrink rate of individual grains of ice
463 + 1 = 464
Orbital parameters
464 + 3 = 467
Glacier, soil, and snow emissivity
467 + 3 = 470
Reynold's number calculation for small turbulent eddies in/across snow
470 + 2 = 472
Plant aerodynamic properties 💨🌱
472 + 72 = 544
Eighth-order polynomial fits providing water vapor pressure and its derivative
544 + 36 = 580
Bedrock thermal conductivity
580 + 1 = 581
Weight of rain or snow that a canopy leaf can support
581 + 2 = 583
Estimation of microtopography
583 + 2 = 585
Hydraulic conductivity of ice and dirt
585 + 16 = 601
Melting snow self-cleaning & compaction
601 + 12 = 613
Plant stomatal resistance
613 + 22 = 635
Photosynthesis rate dependence on temperature
635 + 18 = 653
Plant functional type parameters
653 + 44 = 697
Photosynthesis photon conversion efficiency
697 + 4 = 701
Plant root distribution parameters
701 + 24 = 725
Urban construction materials
725 + 54 = 779
Leaf molecular ratio and respiration model parameters
779 + 36 = 815
Nitrogen fixation rate
815 + 4 = 819
Plant carbon/nitrogen allocation parameters
819 + 184 = 1003
Decomposition rates
1003 + 34 = 1037
Turnover rates for century model
1037 + 23 = 1060
Nitrogen fixation rate
1060 + 3 = 1063
Plant mortality
(interesting that it is called out as a 'gross oversimplification of an important process')
1063 + 1 = 1064
Lightning strikes and rate of fires started per person per month
1064 + 5 = 1069
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