The MOST biofuels will ever do is add to and recycle pollution and GHGs. Here are some basics:
Fossil fuel use and agriculture move carbon and GHGs from the ground into the atmosphere.
Biofuels take carbon from the atmosphere and recycles it back into the atmosphere with necessarily additional agriculture, IF the same numbers of people are to eat.
Many “improved” agricultural practices depend upon additional fossil fuel based and GHG producing fertilizers, which then also move from the ground into the atmosphere as additional GHGs.
Fossil fuel energy used to make biofuels usually exceeds Biofuel energy produced, plus some useful co-products though.
Burned Biofuels are no cleaner than burned Fossil fuels for the air we breathe, then add biofuel production pollutants.
Best estimates are that “at scale” cellulosic ethanol is decades away.
We need Carbon Capture and Storage (CCS), which would capture CO2 from coal fired electricity plants, for example, and returns the concentrated CO2 back to the Earth, thus NOT allowing the CO2 to add to our high and growing atmospheric CO2 levels. The once truly great Dr. Craig Venter has a synthetic biofuel cell which needs concentrated CO2 to grow, so he wants to use the CCS captured and concentrated CO2 for his biofuel, which would blow all the CO2 right back into our atmosphere. His synthetic biofuel cell is the ultimate irony of all biofuels, they worsen the problem they propose to solve, they keep in the atmosphere what needs to be returned to the earth, quickly.
Truly “Green” fuels get electricity or heat from wind, solar, geothermal, hydrogen, some hydro, or any other non-carbon base. Even nuclear has a place today because of the urgency of reducing our GHG emitting habits. Currently, we need to put carbon back under (like in caverns) and onto (like in trees) the ground, not just recycle it with GHG, water, and fertilizer intensive Biofuels, which necessarily change carbon storing land into carbon releasing lands minimally.