This chapter provides an overview of sources of greenhouse gases and their relative contribution to global warming. The difference between reserves and resources of fossil fuels is explained, indicating current and future availability for each. The contribution of nuclear energy and renewables to global energy resources is discussed and their role along with fossil fuels in electricity generation and infrastructure, cogeneration and community energy. The role of carbon capture and storage in reducing carbon dioxide emissions from power generation and carbon-intensive processes is explored. The rest of this chapter evaluates the contribution to GHG emissions from buildings, industry, transport, waste, agriculture and land use as well as the importance of the biome, oceans and other water bodies as carbon sinks.