However, the amount of mining is not dependent on the amount of transactions.

Entertain my ignorance on this for a second, but isn't there some sort of dependence here? Like not a strictly casual dependence, but if transactions were, say, to magically halve for a few days, would that not affect the mining required and thus the total energy expenditure of the mining?

(Obviously the limit case would show this to be true, in that in the absence of any transactions at all, mining would cease. But I'm after something a bit more clearly casually related, somewhat like supply and demand in the marketplace – consumption of beef driving more supply and more methane, e.g.)