Many of you have put more detailed thought into this issue than I have. My high-level understanding of the issue that faces us boils down to this, I think:
1) We can be certain enough that we (mankind) are causing climate change that we should be obligated to act to address it. As CD says, 90% should do it.
2) While the cost studies are imprecise, there is a very real cost to unmitigated climate change that will likely dwarf expenditures we could take now to attempt to combat it. Among those costs are social instability and warfare that come from dramatically shifting availability of resources.
3) Policy makers rarely seem willing to address those future costs.
4) We, as a people (and probably not just in the United States) seem to have no understanding of how our behavior impacts CO2 emissions. The cost of making and transporting an item is something we have very little concept of even without the inclusion of the carbon footprints associated with those activities. So although we may know the price of beef consumption in dollars, we have no grasp of its CO2 footprint (nor the footprint related to streaming video on our mobile devices).
5) The only currently realistic way to generate enough energy to reduce our CO2 emissions enough is widespread new nuclear production. However, because of the catastrophic risks associated with melt down (and other potential disasters/security issues), and the high capital investment required to build nuclear plants, there is no appetite to build nuclear infrastructure. Moreover, the people who are politically most motivated to address climate change--the Democratic left--are also generally opposed to nuclear energy. That's a difficult hill to climb. Similar to the disposal of nuclear waste at Yucca Mountain (or anywhere else like it), there is an ideological purity that makes perfect the enemy of the good, and demands the impossible rather than accepting the flaws inherent what is possible.
6) There are major economic interests in many sectors of our economy that would suffer if we took a serious look at CO2 emission reductions: those include energy production (primarily oil and gas--coal is populist red meat, and already economically lost), transportation, food production, and even manufacturing, because transportation of foreign-made goods is a serious issue contributing to our CO2 footprint.
Which brings me to my final, depressing point. We likely know what we have to do to accomplish the reduction of our CO2 output to a level that isn't extremely dangerous to us as a species, and even more our current cultural identities, but we don't have the political will because it will be very disruptive to our current socio-economic structure. The saddest part about this is that many of the changes we could make--building nuclear power, updating our power grid, updating our transportation infrastructure (including a transition to a bigger rail-hub system and electric vehicles for final distribution), and including CO2 emission in the cost of producing goods (which would assist in returning more manufacturing to the United States), and changing our dietary standards (less meat, fewer processed foods)--would provide overall benefit to us as a nation beyond merely reducing our emissions and addressing the climate crisis.
Nonetheless, marshaling the political will to take on these important tasks seems beyond our current capability. One of the--but hardly the only--reasons for that is the powerful economic interests opposed to what they will lose if we make a significant investment in addressing climate change. While the oil and gas industry leads that charge, it is not alone.
