Carbon-based fuel
From the perspective of climate and ecology , biofuels and fossil fuels have in common that they contribute to the production of atmospheric carbon dioxide , which has emerged in recent decades as the fastest-changing greenhouse gas , whose principal impacts are global warming and ocean acidification . However biofuels actively participate in the carbon cycle today by photosynthesizing carbon dioxide , unlike fossil fuels whose participation was long ago , and can therefore in principle bring atmospheric CO2 into an equilibrium not possible with the continued use of fossil fuel . 
<triplet> atmospheric carbon dioxide <subj> greenhouse gas <obj> instance of