Uncharted Territory

November 3, 2010

Biofuel Payback Periods Revisited

Filed under: Biofuels, Energy policy, Global warming — Tim Joslin @ 6:59 pm

Deepak Rughani from Biofuelwatch was the star of a Campaign Against Climate Change conference last Saturday on the theme Zero Carbon by 2030.  Deepak emphasised the importance of preserving ecosystems for the many services they provide, and not just engaging in carbon bean-counting.  His talk is well worth hearing if you get the chance.

Unusually, the conference was not a totally whole-hearted group hug.  Deepak disagreed with the latest Zero Carbon Britain (ZCB) report which proposes the use of willow and miscanthus as biomass crops in the UK.  If I recollect correctly, he noted that such crops require the full commercialisation of cellulosic ethanol production technology – currently only at the pilot stage – and that willow stands store only maybe 25% of the carbon of natural woodland (miscanthus less) at the expense of biodiversity.  He didn’t mention that willow is notoriously thirsty.  I would also go on to point out that the land for such crops is only made available, in the ZCB plan, by a drastic reduction in meat consumption.  It’s unclear to me how the ZCB team propose to bring about such a change in eating habits.  My main criticism of the ZCB 2030 report, though, is that it still underemphasises the benefits of internationalising the problem.  It makes some comments on a European and North African Supergrid, and bangs on about different peak loads in the UK and Norway, but still relies on domestic electricity production, rather than considering the potential and cost-effectiveness of solar thermal electricity in North Africa.

But what stuck in my notebook from Deepak’s talk was a point he made about biofuel from Indonesian palm oil.  A peer-reviewed paper, he said, had determined that clearing the land to grow the oil palms would incur a “carbon debt” that would take up to 840 years to pay off.  My ears pricked up.  This sounded very like the “pay-back period” concept I came up with in 2007, and documented in three papers.

I’ve now tracked down the paper Deepak was referring to, despite my notes referring to someone called “Fagione”.  The paper is actually Fargione et al, from Science vol 319, no. 5867, 29 February 2008, p.1235, and it’s titled “Land Clearing and the Biofuel Carbon Debt”.  You can download it yourself for free if you register with Science.  Curiously, the last page of Fargione et al included the start of another article by Searchinger et al on the same topic, entitled “Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change” so I downloaded that, too.

Fargione et al indeed estimates how long it would take for avoided fossil-fuel emissions (due to the use of biofuels instead) would take to compensate for the emissions from clearing land for biofuel feedstock production, in a variety of scenarios.  Searchinger et al instead amortise the land-clearance emissions over 30 years in order to compare carbon emissions from biofuel with those from gasoline.

I’ve pored over these two artefacts and I’m afraid I have to report that the scientific community has made a smidgeon of progress, but isn’t quite there yet.  I’ve had the benefit of an education at a prestigious university and I have to say if I’d handed in work like these two papers I would have expected a “good effort but must try harder”, B-.  Very disappointing after I put the answers in the public domain in The Biofuel Papers.

The bottom-line is that the scientists massively understate the case against biofuels.  There are a number of points in my critique, so I’m even going to number them:

0. Meta-critique: the Perils of Peer-Review

I’m going to save this one for a separate post.  Nevertheless, I can’t help noting, passim, a familiar twinge of irritation.  It would be so helpful to know who the reviewers of these papers were, and especially what points they raised.  I am forced to guess that much time and effort was spent checking the methodology used to produce the numerical data; less, or at least not enough, on the overall line of reasoning; and little on the comments and discussion which are actually the most interesting part.  The effort is especially misspent in this case as accuracy is not important.  Ballpark is fine for showing that biofuels will not help us stave off dangerous climate change.  We’re not trying to disprove the general theory of relativity, here.

1. An Invalid Implicit Assumption: the Displacement Fallacy

Both papers rest on the assumption that producing biofuels – say for use in road vehicles – will somehow “displace” the use of fossil fuels.  This will not be the case.  I laid out the argument quite some time ago in a short paper entitled The Displacement Fallacy (pdf).

I find it quite astonishing that neither the authors nor, presumably, the reviewers of papers in a prestigious scientific journal even consider the validity of such an assumption (or perhaps even its existence), especially as the paper goes on to imagine biofuels being produced for centuries.  The implication would be that we’re continually “displacing” the same fossil-fuel from being burnt!

As I argued in The Biofuel Papers, when trying to justify the use of biofuels, it might make sense to use a simplifying assumption, for example that half the time you’re displacing fossil fuel use, and half the time you’re not (very generous to biofuels, in my opinion, especially over a long time period).  This would, for example, double Fargione et al’s pay-back period for palm oil on converted peatland to 1680 years.  That for sugarcane ethanol would be 34 years rather than 17 and corn ethanol on abandoned cropland would be 96 years rather than 48.

2. Completing the Argument (i): the Importance of the Timing of Emissions

The basic argument in both papers is that clearing land to produce biofuels releases carbon which takes many years to offset by displacing fossil-fuel emissions through the production of biofuels.  But this isn’t the whole story, as Fargione et al notes:

“…biofuel production can displace crops or pasture from current agricultural lands, indirectly causing GHG release via conversion of native habitat to cropland elsewhere”.

So maybe we should be looking at the problem in the round.  Perhaps we should simply be making an assumption about whether or not we need to clear land to produce biofuel feedstock.  Again, 50% seems a good figure to choose, since we can imagine that half the time the total cultivated area is increasing and half the time it is shrinking.

But how do we deal with this general case?

The answer is that what we’re really concerned about is how long extra CO2 emissions remain in the atmosphere, because all that time they’re capturing extra heat.  The amount captured per tonne of CO2 depends on the atmospheric CO2 concentration at any given time, but that’s an unknown, so let’s simply assume we’re concerned about extra tonne-years of CO2.

For example, in the case of palm oil grown on converted peatland, it takes 1680 years to offset the emissions from the initial land conversion, that is, to reverse the initial increase in the atmospheric CO2 concentration.  But it’ll take another 1680 years to compensate for the time the initial release of CO2 spent in the atmosphere.  So paying back our initial carbon debt will actually take 3360 years!

But in the general case, we “only” have to add 50% to our payback periods, because on average the biofuel will only result in land clearance 50% of the time.  The payback period for sugarcane ethanol becomes 51 years (34 *1.5) and that for corn ethanol on abandoned cropland is 144 years (96 * 1.5).

3. Completing the Argument (ii): the Importance of Foregone Carbon Sequestration

But this doesn’t sound quite right, does it?  Surely, if the land doesn’t have to be cleared we wouldn’t have a carbon debt to repay.  Surely we can’t allow for extra tonne-years of atmospheric CO2 removal to compensate for initial land clearance and a probability of the land not having needed to be cleared?

Actually, yes we can.  Because the cost of the carbon emissions from the potential ecosystem on a given area of land are incurred regardless of whether you physically clear it before starting biofuel production.  Both papers recognise this, but have not taken it into account in their calculations.  Fargione et al write:

“…if land cleared for biofuel production had been accruing carbon (we assumed lands were at steady state), the debt would be increased by the loss of this future storage”.

Well, OK, but eventually the land would reach a maximum carbon carrying capacity.  Hence, as I just said, our starting point needs to be the amount of carbon in the potential ecosystem on a given area of land (actually the carbon in the ecosystem potentially cleared as a result of cropping the biofuels, which worsens the case e.g. where soya bean production is displaced from cerrado into rainforest, but for simplicity’s sake I’m going to ignore this wrinkle).

Searchinger et al give the matter considerably more thought:

“Even if excess croplands in the United States or Europe became available because of dramatic yield improvements beyond existing trends or the release of agricultural reserve lands, biofuels would still not avoid emissions from land-use change. Truly excess croplands would revert either to forest or grassland and sequester carbon. Use of those lands instead for biofuels sacrifices this carbon benefit, which could exceed the carbon saved by using the same land for biofuels. In addition, even as cropland declined in Europe in recent years, changing technology and economics led cropland to expand into forest and grassland in Latin America. Higher prices triggered by biofuels will accelerate forest and grassland conversion there even if surplus croplands exist elsewhere. Most problematically, even with large increases in yields, cropland must probably consume hundreds of millions more ha of grassland and forest to feed a rising world population and meat consumption, and biofuels will only add to the demand for land.” [my emphasis]

4. The Correct Line of Reasoning

This is laid out more fully in my essay Biofuels Are Not the Answer (pdf) and my systematic treatment Biofuel Payback Periods (pdf).  But to summarise using the examples from Fargione et al:

Principle: Compare growing biofuels with not growing biofuels – an alternative policy of letting the land revert to its natural state.

Step 1: How much carbon would the land store if we didn’t grow biofuels?

E.g. In Indonesia the peat bog would store around 6000 tonnes CO2/ha according to Fargione et al (this figure is in the text rather than the table, which uses a lower figure based on only 50% of the emissions from land clearance occurring immediately, but as Fargione et al note, they should in fact all be included), the cerrado 165 tonnes and the abandoned cropland 69.  But in the last case the land is still taking up carbon so we have to take a figure for natural grassland, which is considered in the paper (which is thereby simplified) of 134 tonnes/ha.

Step 2: How many years biofuel production would save the same amount of carbon if it replaced gasoline?

These are the figures given by Fargione et al of 840 years (in the text) for the palm oil on peatland; 17 years for sugarcane on cleared cerrado; and 93 years for corn ethanol on the Great Plains (potential grassland).  The data must be based on complete life-cycle emissions of both the biofuel and the fossil fuel.

Step 3: Allow for only 50% success in replacing gasoline (generous, especially for the centuries required to justify cultivating peatland).

Doubling our figures gives 1680 years for the palm oil on peatland; 34 years for sugarcane on cleared cerrado; and 139.5 call it 140 years for corn ethanol on potential grassland.

Step 4: Allow for the timing of land clearance at the start of the cultivation, probability 50%.

Adding 50% to our figures gives payback periods of 2520 years for palm oil on peatland (note even the deferred emissions are rapid compared to this timescale); 51 years for sugarcane on cleared cerrado; and 210 years for corn ethanol on potential grassland.

5. What does this analysis mean?

We need to be a little bit clearer about our conclusions.

We’re going to be worse off in terms of the heat captured by the atmosphere – global warming – for the periods given if we produce biofuels than we would be if we didn’t, if we simply left the land alone.  I repeat, the planet will be hotter, more ice will melt, if we do grow biofuels than it would be if we don’t.  And that’s before we consider any other benefits of the natural ecosystems replaced by biofuel monocultures, such as biodiversity, water retention and purification and so on.

And we may never reap the benefits for the simple reason that the biofuel production may not be sustainable.  Soils may become too depleted to maintain yields and global warming may kick in.  Climate change combined with cultivation rather than maintenance of a resilient ecosystem may result in desert replacing the biofuel crops long before the end of the payback period has been reached.

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1 Comment »

  1. [...] This meant biofuels. I’ve written previously at length about this folly, most recently here. RTFO, folly, policy, maybe we should talk about the “follicy”, the [...]

    Pingback by The UK RTFO – Electricity Should Count « Uncharted Territory — May 27, 2011 @ 4:15 pm

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