If we went dead neutral on carbon tomorrow the carbon level would slowly drop back to whatever it's stable point is, or you could slowly manually reduce it through sequestering, 'biofuels' being a somewhat loose term for anything that basically absorbs in production the cabron it releases in burning at a turnover rate of months rather than geological epochs, if you're sequestering carbon by burning carbon neutral fuel you end up with less atmospheric CO2... not really my interest though. This is noteworthy primarily because even with fission or fusion or solar or wind you have difficulty storing the energy for mobile applications and even the best new battery designs tend to have fewer J/kg then crap fuels like Ethanol, such that the mass of the batteries, even if you lost nothing in charging them and keeping them charged, can represent a massive loss of efficiency. Insofar as fossil fuels are a limited commodity we need something to replace them that represents an optimum of $/kg and J/kg, right now fossil fuels run us around $1/kg and 47 Mj/kg, around 8 cents a kWh... ideally we need something better or parallel as a portable power source, currently biofuels are the only things seriously on the radar for that, we can have a lower J/kg for most applications... most peoples gas tanks when full weigh in at under 10% of vehicle mass and you'd lose little efficiency (especially as vehicle mileage is not linear to mass) by doubling the fuel mass for the same mileage so where biofuels are concerned for cars it's almost all about $/J or $/kwH or $/Mj... what's advantageous, especially to the US which has much coastline and saltwater but relatively little seawater food production, is that algae is not using land we might want to put crops, houses, trees, or solar/wind stuff on thus minimizing the extra costs from competing resource production... now, if 30% of their costs are effectively eliminated by this techniques, that would mean a theoretical 130 MJ of biofuel (a gallon of gas), if it were currently selling for $5, would suddenly be selling for about $3.33... presumably that would be good, assuming of course the $5 figure was 'real' and not a subsidy figure with a real cost of $8 of course.

Now in theory, if we got ourselves some stationary cheap fuel - nuclear or good solar - one could further ramp up production of something like algae by growing it in massive underground cisterns artificially lit to maximize biomass/volume production under pure red LED light. Even if we had some gigantic fusion reactor, barring batteries that are truly superior to chemical fuels in all important aspects you might see huge underground cisterns laced with red LED lights and some algae like this for spewing out fuel, even if the ultimate efficiency of the process resulted in only 10% of the juice from the reactor being available to the end fuel. It's all economics, least cost for energy, this cheapens harvesting, if you look at man hours for calories of wheat vs strawberries for instance, labor is whole orders of magnitude higher for calorie and that's why a pint of strawberries ~ 700 kcal for a couple bucks versus a pint of flour ~ 900 kcal at about 50 cents, and both have much of their cost being transport and storage. This dynamic, along with cal/acre, is the major feature of human diets over the centuries and the same applies to fuels.