CNN: It’s the ultimate business plan: Take something people are willing to pay to get rid of, and sell it to someone else. That’s exactly what a handful of small but well-backed companies are doing – or are trying to do – with carbon dioxide, the main culprit behind global warming. The companies include: Blue Source, a firm half-owned by the the private equity group First Reserve; Hydrogen Energy, a joint venture between BP (BP) and the mining giant Rio Tinto (RTP); Edison Mission, …