[QUOTE="George"] While over-population *is* a problem on a global scale, which nobody seems to want to tackle head-on, the local effects are nothing new - we've had high population densities for hundreds of years. In fact within those major conurbations, the air is cleaner now than at any point in their existence... despite the increase in the use of fossil fuels and energy in general.[/QUOTE] Do you see any causal effect between the Clean Air Act and cleaner air now? It didn't happen by accident and industry did not clean up voluntarily. The US auto makers pissed & moaned about govt interference while the Japanese auto makers got their engineers working on meeting the specs. More than once the US auto makers have claimed the new standards were impossible to meet, then met them. As a group, they're a lazy yet greedy bunch, a dynamite combo. The Clean Water Act has had a similar effect on our water. But the current concern, as I see it, is that the Bush administration is relaxing existing standards and permitting increased pollution. The US has a lot more people & vehicles now, so no rational person doubts whether the air will get cleaner or dirtier.