Bioenergy is the largest source of renewable energy and supplies approximately 10% of global energy demands. This is composed of all biological matter stored in plants and organisms, living or recently deceased. Fossilised remains are not counted, as these are not readily renewable. Bioenergy is the term used to encompasses the conversion of biomass into a biofuel. The former being exploited to produce the latter. Early humans that burned wood for warmth were probably the first to convert a biomass into a biofuel. Energy derived from wood based sources are still commonly used in less developed countries, but they are increasingly fed into power plants to amplify electricity prodcution. Increasingly, vehicles are being converted to use ethanol, soy and rapeseed oils as biofuels. Biofuel's produce significantly lower quantities of greenhouse gases than petroleum. Unlike other sources of renewable energy, bioenergy is not zero-carbon. It can also be overexploited and used at a rate faster than can be reproduced. Nevertheless, biomass is typically sourced locally with a production capacity in the control of local communities. The greenhouse gases produced can be re-extracted from the atmosphere, as long as trees are replanted and land isn't degraded by intensive farming.