Related by context. Frequent words. (Click for all words.) 64 fossil fuels 59 fossil fuel 56 Fossil fuels 55 finite resource 54 nonrenewable 49 byproducts 48 greenhouse gasses 48 aquifers 48 Landfills 48 burning fossil fuels 47 carbon dioxide 47 underground aquifers 47 renewable 47 crop residues 46 landfilling 46 greenhouse gases 46 carbon sinks 46 resources 45 minerals 45 landfills 45 chemical fertilizers 45 mineral extraction 45 synthetic fertilizers 44 CO2 44 methane 44 groundwater 43 crop residue 43 alternative energies 43 biomass 43 carbon sequestration 43 biosphere 43 Mother Earth 43 tar sands 43 feedstock 42 GHGs 42 irrigated agriculture 42 renewable energy 42 ecosystems 42 recyclable materials 42 coal 42 ecological 42 biofuel crops 42 liquid fuels 42 arable land 42 nonpolluting 42 bio fuels 42 refrigerants 42 environmentally harmful 42 harmful pollutants 42 carbon dioxide methane 42 fertilizers pesticides 41 greenhouse gas 41 underground aquifer 41 environmentally benign 41 alternative fuels 41 woody biomass 41 raw materials 41 biofuels 41 overexploitation 41 ozone depleting substances 41 energy 41 wean ourselves 41 wildlife habitat 41 heat trapping carbon dioxide 41 environmentally sound 41 greenhouse gas emissions 41 sequester carbon 41 monocultures 41 carbon dioxide emissions 41 groundwater pumping 41 fragile ecosystems 41 greenhouse emissions 41 recyclable 40 landfill 40 feedstocks 40 ocean ecosystems 40 boreal forests 40 Alberta tar sands 40 topsoil 40 tarsands 40 nitrogen fertilizers 40 croplands 40 hydroelectricity 40 petroleum 40 landfilled 40 natural gas 40 carbon dioxide emitted 40 environmental impacts 40 biomass fuels 40 harmful gases 40 CFCs 40 ecologically 40 carbon emitted 40 airborne pollutants 40 environmentally destructive 40 extractive industries 40 polluting 39 nutrients 39 woody debris 39 hydrocarbons 39 distillers grains