The price of energy is determined almost exclusively by supply side factors Richard.  Investment in production capacity has been reduced by a glut of supply that has eroded prices.

Demand is, as The Snoman points out, remarkably price inelastic, and is very closely tied to economic performance. For example, the only time demand fell during the past generation was in 2008-09.

While it is apparent that some individual choices have been affected by price over time, the impact on overall energy demand has been negligible.   

Given this reality, its pretty clear that carbon taxes are much more about taxes than they are about carbon.