True or false: Biofuels reduce the carbon footprint and help fight climate change.

This is quite true, but it is not that simple.

First, and contrary to what some people think, a biofuel is not more "bio" than its fossil equivalent at the time of combustion. They contain the same molecules that always emit the same quantities of GHGs, whether or not they are labelled "bio". A cargo ship running on biodiesel or bio-LNG will emit as much GHG as one running on fossil diesel or LNG. And the same goes for airplanes (kerosene vs. bio-kerosene).

It is therefore false to say that biofuels reduce the carbon footprint when the fuel enters the combustion chamber. Chemistry is very strict on this point.

However, when we look at the life cycle analysis of the fuel (LCA), the situation is different. When a fossil fuel is used, 1 ton of fuel is extracted from the ground, and this fuel will emit 3 tons (roughly) of GHG. On the other hand, if this fuel is produced from biomass, corn for example, when the corn grows, it absorbs, via photosynthesis, CO₂ from the atmosphere (3.4 tons of CO₂ is a realistic number). This corn is then converted into biodiesel and this industrial process will consume energy and possibly intermediate products that will emit GHG/CO₂ (e.g. 1.5 tons). The total GHG balance after combustion of the biofuel will therefore be: 3 t (emissions during combustion) + 1.5 t (emissions during manufacturing) - 3.4 t (absorption during the growth of the corn), i.e. 1.1 t.

This biofuel will emit 1.1 t of GHG instead of 3 t for its fossil twin, and it will have reduced its carbon footprint (compared to fossil) by 63%. Each biofuel is a special case, and the same biofuel can have different coefficients depending on where and how it is manufactured. And it is even possible for a biofuel to be worse than its fossil equivalent, depending on its own LCA!

Let us add that the place where GHG are emitted (at sea level for cargo ships, at 12,000 m for airplanes) is not neutral, but its impact is still rather insufficiently understood (especially at high altitude).