The injection of gases such as carbon dioxide (CO2) and perfluorocarbons (PFCs) into the atmosphere of a developing planet is an essential first step in the terraforming process. These greenhouse gases trap solar heat and raise the mean temperature to a sufficient level where a self-sustaining ecology can be initiated. PFCs are up to 10,000 times more effective than carbon dioxide as a greenhouse gas, but they do not occur naturally in planetary environments, and large quantities must be transported to any planet undergoing terraforming.