You see, it's not that simple. A Hummer can theoretically also run on a renewable fuel like biodiesel or use some other eco-friendly stuff like fuel cells where the electricity to split hydrogen was obtained from water/wind turbines installed in some very remote areas. I think I mentioned it a couple of times in this forum, but, there's a HUGE difference between limiting the level of consumption and a way of securing it. Let me give you a simple example. Say, some 12,000 years ago the humanity grew in numbers and, as a result of the not-very-eco-friendly way of securing food (i.e. the hunting), the amount of food shrunk considerably causing a famine. That was a first global ecological catastrophe the humanity ever knew. So, two options came alive. First, limit the amount of consuming food (i.e. somebody had ceased to live). Second, move to the agricultural civilization and go on eating and grow in numbers. Apparently, the humanity went the second way. Consequently, several other ecological disasters loomed over the millenia. Like, people could no longer burn the forests before planting their grain and move on burning other forests, but rather switch to the more settled way and just swap fields rather than constantly looking for new ones. Even in the beginning of the 20th century there was danger of famine as the land was unable to sustain that many people. So, the fertilizers were invented and used. And later on a similar problem was solved by means of the GM-food. And each and every time the humanity was faced with the request to limit consumption and yet it went on and on evading the dangers. So, now you're saying the "1,80$ per litre" would do the trick?