Related by context. Frequent words. (Click for all words.) 56 cleanest 53 environmentally sound 51 efficient 51 cleaner greener 51 environmentally benign 50 economical 49 greenest 48 environmentally friendly 48 Fossil fuels 48 greenhouse gas emitting 47 reliable 46 fossil fuels 46 nonpolluting 46 dependable 46 technologically advanced 46 environmentally sustainable 45 safest 45 safer greener 45 ecologically sound 45 environmentally damaging 45 carbon emitting 45 dirtiest 44 economically viable 44 technologically feasible 44 cheapest 44 environmentally 44 renewable energy 44 cleaner 44 environmentally responsible 43 biodiverse 43 polluting 43 fossil fuel 43 renewable 42 potable 42 economically advantageous 42 prosperous 41 civilized 41 waste disposal 41 filthiest 41 Cellulosic ethanol 41 livable 41 plasma gasification 41 Enriched uranium 41 sustainable 41 potable drinking 41 Renewable energy 41 affordable 40 carbon emitter 40 industrialized 40 finite resource 40 livable communities 40 potable water 40 friendliest 40 economically feasible 40 energy 40 alternative fuels 40 modular scalable 40 hydroelectricity 40 unpolluted 40 governable 40 liveable 40 useable 40 economically prosperous 40 environmentally sensitive 40 seismically active regions 40 polluted rivers 39 renewables 39 lignite coal 39 Bioethanol 39 electricity 39 technically feasible 39 smartest 39 Hydrogen 39 ecologically sustainable 39 viable 39 ecologically 39 zero emission 39 environmentally destructive 38 unspoiled 38 guzzler 38 biologically diverse 38 usable 38 windpower 38 wean ourselves 38 eco friendly 38 inexhaustible 38 ecofriendly 38 desalinization 38 Landfills 38 drinkable 38 Gasification 38 industrially 38 baseload 38 liquid fuels 38 geo thermal 38 environmentally conscious 38 polluted 37 atomic reactors 37 reducing carbon emissions 37 diesel powered 37 fertile soils