1. A low carbon economy aims to minimize greenhouse gas emissions, especially carbon dioxide, through energy efficiency, low carbon energy sources, and managing terrestrial carbon in forestry and agriculture. 2. Modeling estimates that technologies available at less than $100 per tonne of carbon dioxide avoided could reduce emissions by 16-30 billion tonnes in 2030, cutting emissions 30-50% below business-as-usual levels. 3. Building, agriculture, and forestry offer the most potential and lowest costs, accounting for 65% of total reduction potential in developing countries.