Economic models are hopeless as far as a scientific models go.
Now, I don’t know what Gratham’s logic is, but I do know of the report that he recently put out.
If you look at just oil. Exploration costs are >$60 dollars(this will only go up). So, if market value dipped under that, the industry pretty much shuts exploration down. Which would be disastrous in the age of peak oil because of declining old fields. When oil fell to $34 the whole industry started screaming.
Anyway, energy has a unique flow through effect on most commodities due to the fact that they are all energy intensive to produce.
So, I would say, that right there will keep commodities up. No model needed.