We are often talking about how the rapidly decreasing biodiversity of the world is a grave problem, and I for one I believe that we are (at least in part) justified. We do not however talk how our society lack of diversity (wait I will explain what I mean) is a big problem. I do not mean diversity of people, (even if we could have a greater) but more like the diversity of our base technology. I find that most of our civilization is based on very few principles: petroleum combustion and electricity (to name two).
Our reliance on these might be one of the reason we have a pollution problem. A single petroleum car (or even an hundred) isn't much problem (if any) however a hundred millions or a billion car all spitting CO2 in the atmosphere is a great problem for the equilibrium. The "solution" would seem to be replacing all those car with something else that is less polluting. However, that probably wouldn't work, none of the propose solution when applied to the scale we need them would be ecologically friendly: Hydrogen car produce water vapor which is a greater green house gas then CO2, Ethanol production produce more green house gas then petroleum burning and production, Electricity... well very little electricity is produced with eco-friendly methods (and our hydroelectricity production isn't that ecological). Apply any of those solution on the scale needed to replace petroleum and you create a similar problem (maybe even a worse problem).
A better alternative might be to diversify our technological base, it would still be a problem since the large number of human and the large use we makes of our technology will produce a lot of pollution. However a larger technological base would reduce the quantity of each poluant, perhaps to a manageable level. It does have a problem tho, everything would probably cost more, since our level of price depend on mass production. Reduce the number you produce of something and you will drive the cost up, but it might be the only way to reduce our pollution production.