For instance one I have used about paper is that if we accept the fact that Europeans use on average around 300 kilos of paper fibre a year per capita, and in China the figure is 9 kilos, then if the per capita consumption in China was to rise to European levels, it would require 140.000 new paper mills to supply that increased demand. If people know the size of a paper mill, they then realize the size of the problem.
The biggest disconnect I have found is that people fail to understand big numbers. And not only that, but they fail to understand that individual actions which do not appear to them to be a problem, when multiplied a million times, become a huge problem.
For them, for instance, buying a plasma TV is a matter of choice: "I can afford it" even if it uses 6 times more electricity. And indeed one plasma TV has no effect on national electricity consumption. But when a million people buy a plasma TV, it needs a dedicated nuclear reactor. You can't be me, I'm taken