I didn't intend to start a political discourse on carbon dioxide and climate change. In a nutshell, the problem is not steady state carbon dioxide and water vapor, but the INCREASE in carbon dioxide from extracting long buried carbon and setting it free into the atmosphere. So elephants are good, as they consume and emit carbon in a closed loop, neither increasing nor decreasing atmospheric carbon content. The same goes for horses pulling railcars, or people for that matter, as long as they don't extract ancient fossilized carbon. Now we can go back to enjoy steam locomotives that by this time only emit the tiniest fraction of human fossil carbon release. As for the rest I would vote for nuclear, solar, wind, geothermal, and other renewable energy sources (and more elephants).