One of my most favorite social commentators is George Will. Recently I read an article from him that said that the earth doesn't care what is done to it or for it. His main point is that over "geologic" time (i.e. extended time millenniums, millions of years, etc..) what we do to the earth is so minimal as to barely register. He notes the amount of rain that falls on the earth to illustrate that we should all be flooded out yet we are not drowning on a global scale.
The article raises some good points when one thinks about the big picture and that is necessary from time to time. Comparing our present few generations to geologic time, George Will is right (i believe) that whatever happens will just be a blip and the earth will survive. After all the earth survived ice ages. We can be so short-term near future focused that we forget to look at history or into the future 20,30 even 1000 years.
A second way this works, however, is that we neglect responsible environmental stewardship because we don't look beyond our present situation to see the unintended consequences of our actions.
The earth did survive an ice age, but would it not be terrible for us all to go through another ice age? So I suppose it's really a decision of what is the issue: 1) altering the earth over geologic time or 2) having an unnecessary environmental impact that could seriously alter our lives in the near term future.
Regardless of where you come down on global warming, there are numerous reasons why we need to reconsider our use of fossil fuels:
1) dependence on unstable regions of the world (Iraq, Saudi Arabia, Angola, etc...),
2) complicated extraction methods which among other things lead to oil spills or the death of coal miners,
3) dirty air leading to respiratory illnesses and general unpleasentness,
4) social dependence on a non renewable and depleting resource, etc...
So for me global warming or the fear of altering the earth over geological times is not the issue as much as it is being a good steward of God's good creation and keeping the bigger picture in mind for our children's lives.