Cassandra has moved. Ugo Bardi publishes now on a new site called "The Seneca Effect."

Monday, October 30, 2017

Biofuels: Can They Save the Airlines from the Seneca Collapse?

Painting planes green is much easier than making them run on biofuels.

"Can the airlines be run on biofuels?" As it often happens, this simple question doesn't have a simple answer. First of all, it is a question that makes sense only in terms of a "sustainable" plane, that is one that doesn't run on fossil fuels. That's a major technological problem. Whereas cars can be made to run on battery-powered electric motors, the power/weight ratio of the combination is simply unacceptable for a passenger plane that could provide a performance comparable to that of current jet planes. Hydrogen planes have been proposed, but they are a nightmare for several reasons and it is unlikely that they could become practical in the short and medium term future.

That would leave only biofuels as a "sustainable" fuel that could power the current fleet of jet planes. Indeed, a small number of tests have been carried out showing that it is possible to fly planes using biofuels. But can it be done on the large scale needed to get rid of fossil fuels?

The first problem is whether biofuels are truly carbon-free. Most likely, the current fuels made from crops are not; in the sense that they involve extensive use of fossil fuels for their manufacturing. In many cases, however, even the current generation ("1st generation") of biofuels can provide a significant saving in the use of fossil fuels for the same amount of energy produced. This is the case, in particular, for ethanol produced from sugarcane in Brazil. But there is a more fundamental question is: what would be the consequences of ramping up biofuel production to the levels needed to power the current airline fleet?

In a recent paper on Nature, Rulli et al. discuss the effect of the large scale cultivation of 1st generation biofuels on various parameters of the world's economy, including the global food supply. They don't specifically examine the needs of airlines, but we can use their results for analyzing this sector. First of all, the total amount of jet fuel consumed in the world is reported to be 6,000,000 barrels per day. It corresponds to about 7% of the total world combustible liquids production. We may consider this value as approximately the fraction of transportation energy used by airlines since crude oil represents 93% of the total energy used in transportation.

Rulli et al. estimate that if we were to arrive at a 10% reliance on biofuels for the world's transport, that would leave food for no more than 6.7 billion people and, since the current world population is about 7.6 billion people, almost one billion people would starve. Now, since the airlines consume about 7% of the world's transport energy, feeding the airlines with biofuels would move us dangerously close to the threshold that would lead to killing a large number of people for the purpose of keeping planes flying.

Of course, these data are for first-generation biofuels. There is much enthusiasm for second and third generation biofuels from cellulosic plant tissues or algae which, theoretically don't impact on the food supply. Sure, but today the production of these fuels is non-existent or at best negligible. How long will it take to ramp up their production to the levels we are discussing here? And are we sure that they will work as promised?

The problem, here, is not just a technological one. We are dealing with a complex system, the world's economy coupled with the planetary ecosystem. In these systems, you can't change just one thing and leave all the rest unchanged. Once we start to produce biofuels on a very large scale, it becomes extremely difficult to stop at a certain threshold. If we have a product and a market for it, both tend to expand and it is nearly impossible to stop the expansion of something that generates a profit.

That would bring big problems, to say the least. Rulli et al. estimate that arriving to supply 1st generation biofuels in an amount corresponding to 20% of the transport energy would leave no more than 4.4 billion people alive in the world. That is, it would kill some 3 billion people. Or, if dealing with 2nd or 3rd generation biofuels, it would lead to whatever disaster generated by the appropriation for humankind an even larger fraction of the planetary photosynthetic activity than it is done today. The ecosystem has limits, after all.

Unfortunately, it is unlikely that ethical considerations would affect decisions in this field. The system is made in such a way that if producing fuels for the rich is more profitable than producing food for the poor, the system will produce fuels, even though that implies killing billions of people. So, we can only hope that biofuels will turn out to be too expensive even for the rich; but that may not be the case. With so much research and development ongoing, production costs might be lowered enough to turn biofuel into an effective weapon of mass destruction (and I wouldn't be surprised to discover that this is one of the reasons why biofuels are promoted so aggressively in some quarters).

Or, more simply, we may hope that the Seneca Collapse of the world's economy will take care of the "airline problem" once and for all. As I said many times, the Seneca Cliff is not a problem, it is an opportunity. In this case, it could lead us to develop better transportation technologies; more efficient and more benign for the ecosystem - although probably slower. But that's not a problem, either. It is an opportunity to travel only when you need to, and to enjoy the trip, too!

 Some further data on the extent of land needed for the cultivation of biofuels for airlines. 
First of all, the total amount of jet fuel consumed in the world is reported to be 6,000,000 barrels per day . It corresponds to about 7% of the total world combustible liquids production. Now, we need to compare the values measured in barrels with the needs of the airlines, measured in liters. A barrel contains 159 liters, so 159*6=1000 makes about 1 billion liters/day, or 3.6x10^11 liters/year. Let's now consider the most efficient biofuel production: ethanol from Brazil's sugarcane. It can produce 6000 liters/ha per year  Note that ethanol is not as energy dense as jet fuel. It has only about 70% of the energy density of gasoline Which means that the airlines would consume 3.6*10^11/0.7 = ca. 500 billion liters of ethanol/year. 
So, assuming that the whole production of Brazilian ethanol is dedicated to airplanes, we would need more than 80*10^6 hectares (eighty million hectares). The total arable land in Brazil is reported to be: 75 Million ha. It means that the whole agriculture of Brazil should be dedicated only to produce fuel for the airlines. 
That is, of course, absurd, but it is also true that the world's total arable land is = 1,407 x10^6 ha (, about 20 times the area available in Brazil. So, the airlines would need only about 5% of the total which is, by the way, just slightly larger than the global arable area used for biofuel production today  (about 4%) But note also that not all the arable land has the same good productivity as the land used for sugarcane production in Brazil, so the real fraction needed would have to be considerably larger than 5%, probably still less than 10%. How many people would starve if we were to arrive to that, it is impossible to say. 


  1. As Kevin Anderson states in a couple lectures, one of the the issue with biofuels is that everyone plans to use it to reduce thier CO2 emisisons, from the shipping industry, to the aircraft industry to BECCS in the power industry... and this arable land is to come from where ?

    That said, it's a couple years old now but Tom Murphy did a post on this that was interesting

  2. Biofuels only has sense to use waste biomass (food excess, non edible farming waste, etc.).
    In other cases, make synthetic (non-bio chemical synthesis) fuels are normally less resource demanding, most times for a order of magnitude or more.

  3. I been hearing that biofuel is just around the corner for fourty years now. The "solar" fuel!

  4. Ugo, you are almost certainy correct that the jet airliner cannot be saved. But that is not the only way to fly. Buoyant flight was abandoned some 80 years ago, but it could be revived. And a cargo airship would be about 20 times as energy efficient per tonne-km as an aeroplane - in other words, as efficient as a lorry, but with no requirement for a huge ground-based infrastructure. And today we could make in a sustainable manner a fuel like Blau gas, which in 1929 flew the Graf Zeppelin around the world.

    1. Oh, yes. Airships are a possibility and I am sure we can also have electric planes; why not? The point is that, right now, we are stuck with the current technology and we can get rid of it only by having the old industry collapse and disappear. That's the beauty of the Seneca Effect.

    2. Yes, I agree that old systems must collapse. But I think it is a little unfair to compare airships to electric planes. The latter are well beyond the horizon. But the basic technology behind airships is a century old.

      The rigid frame is aluminium alloy - and Al is the third most common element in the Earth's crust. The fabric is doped cotton. The gasbags - well, goldbeater's skin is certainly renewable, but dries and frays easily (as well as requiring an unconscionable number of cows), so we might seek an alternative.

      And the whole thing is kept in the air not by aviation fuel, which will almost certainly disappear, burt by helium, which is a renewable resource. On the whole, surely a promising avenue to explore?

  5. One big downside of "slow travel" is that only the rich will be able to do it, because ordinary people have to work for a living, and can only get limited vacation time. Or none, if most people will have to go back to subsistence farming.

    Speaking of airships though, one advantage they have is lots of real estate on the outside of the gasbag to which thin-film solar cells could be mounted (assuming a post-fossil future will be able to produce thin-film solar cells), which could provide for a significant portion, maybe even all of their propulsive power. Especially if the airships can fly above the cloud deck. I'd love to see an airship renaissance, especially if I could afford to fly on one. :)

    1. Hi KevinC

      A few years ago I did the math. Yes, the Hindenburg could have been powered fully by the sunlight falling on its envelope. Cruising power was 3600HP, full power was 5200HP.

      Of course, this assumes the sun is shining. To solve the infamous intermittency problem she would have needed to carry batteries, and that is the fatal flaw: she could then have carried almost nothing else.



Ugo Bardi is a member of the Club of Rome, faculty member of the University of Florence, and the author of "Extracted" (Chelsea Green 2014), "The Seneca Effect" (Springer 2017), and Before the Collapse (Springer 2019)