Learn English – Meaning of the adverb ‘differently’ and its position

I don't think there's much difference between the two. It depends on which word you wish to stress more: which or zero. (Incidentally, I would set it off with commas, but that is a matter of taste.)

This saves all the emphasis for the final word zero:

... which is, of course, zero.

This puts the emphasis on which:

... which, of course, is zero.

There is no difference in meaning, only in dramatic effect. The effect is greater if the sentence is spoken; if it is written, the effect is vanishingly small.

You are right to prefer "global challenges" to "challenges facing the commodities market globally," but both sentences overuse use global. I would suggest dropping the first clause altogether, and recasting the sentence to something like this:

XXX has been described as a solution to the global challenges that face the commodities market during the current economic crisis.

or

XXX has been described as a solution to the challenges that face the commodities market during the current global economic crisis.