Contrails of the airplanes, and how one could use them to inject sulfuric acid in the upper atmosphere to reduce the temperature of the planet. Discussion of other techniques such as spraying sea water, creating algae blooms, etc. Calculations to find out if it actually possible by our current technology and economic structure. Why it is important to research these ideas. What could go wrong using one of these schemes such as: changing weather, ocean acidification, ozone depletion.