Environmentalist: Efforts to attain an overall reduction in carbon use by convincing people to focus on their personal use of fossil fuels cannot achieve that goal.
Conclusion
Convincing people to focus on their personal use of fossil fuels cannot achieve an overall reduction in carbon use.
Evidence
Even if most people changed their personal use, it wouldn't produce a reduction on the scale we need. Only government policies can produce change on that scale.
Evaluate
Given that "only government policies can produce big enough change", how could we argue that ?
Well, the nitpicky objection would be that if the goal is literally just a reduction in carbon use, then if most people reduce their carbon use then there will be an overall reduction. The author is saying, "Yeah, but it won't be reduced enough", but she never stipulated that the goal was . So she is assuming, somewhat nonsensically, that
But, where I would assume this is actually going is the idea that maybe having individuals change their behavior could trigger governments changing their policies. After all, the government is made up of individuals. Maybe if the citizenry becomes more engaged in conserving carbon use, then their representatives in government will shift policies accordingly.
Goal
I would look for an answer that rules out our objection: .