China is working on reducing greenhouse gases and pollution in their major cities (http://www.nytimes.com/cwire/2011/09/26/26climatewire-built-in-a-dirty-b...). Why can't the US do the same.
If the US government requires that ALL (including defense) contracts be carbon neutral, then businesses will rapidly comply in order not to lose those valuable contracts. Other businesses and jobs will be created to help meet the government requirements.
Yes, it will be expensive, but it is necessary. If China can do it, why can't we?