If part of the answer to this question is to make a better life for myself and my family or give my kids a better start in life then consider this:
Just watched Four Corners on ABC about global warming and global dimming.
If it was not for global dimming (caused by pollution) the earth could be a lot hotter (caused by carbohydrates). Pollution is being decreased and therefore global dimming is decreasing therefore global warming is increasing.
The culprits to gloom and doom for the earth (in less than a lifetime!) - the burning of gas, coal and oil.
If nothing else think about it when you next invest.