The present invention invention provides methods, apparatus, and systems for determining greenhouse gas (including carbon dioxide) emissions and energy usage, costs and savings of individuals, families, homes, buildings, businesses, or the like. User inputs specific to an end user are accepted, and one or more of the user inputs are correlated with at least one of historic data and modeled characteristics pertaining to greenhouse gas emissions and energy usage to obtain at least one of greenhouse gas emissions and energy usage corresponding to said one or more of said user inputs. An overall greenhouse gas emissions and energy usage can then be determined for the end user based on the greenhouse emissions and energy usage corresponding to the one or more of the user inputs. A specific impact of a particular user action on the end user's overall greenhouse gas emissions and energy usage may also be calculated.