Many agricultural crops can be turned into fuels. Diesel substitutes can be made from the oil in seeds. The sugars in cereals and tubers can be fermented into ethanol. At first examination, biofuels look as though they might significantly reduce carbon emissions. An agricultural crop takes carbon from the air through the photosynthesis process. When the harvest is processed, and the output used as a fuel, the carbon returns to the atmosphere. Proponents sometimes said that agricultural crops make ‘carbon-neutral’ fuels.
Over the last two years, this simple optimism has been eroded. Two further blows have fallen in recent weeks:
- Nobel winner Paul Crutzen and his team showed that we may have been underestimating greenhouse gas emissions from using fertiliser. The work suggested that emissions of nitrous oxide may be far higher than previously thought.
- Richard Doornbusch, who is attached the OECD, wrote a paper which said: ‘The conclusion must be that the potential of the current technologies of choice – ethanol and biodiesel – to deliver a major contribution to the energy demands of the transport sector without compromising food prices and the environment is very limited.’
The balance of evidence is that biofuels produced from crops grown in temperate climates save very small amounts of emissions. Moreover, the land used for biofuel crops could be used for food or biomass for energy. In tropical lands, biofuel crops may save carbon emissions. But the energy policies of richer countries may be incentivising tropical farmers to cut down forest to grow fuel crops. The effect of this almost certainly outweighs any emissions reductions.
Despite the increasingly prevalent view that biofuels are little or no improvement on fossil fuels, both the EU and the US are obliging retailers to increase the percentage of motor fuels derived from agricultural sources. This is a mistake.
The fundamental problem with biofuels When a temperate crop such as wheat is grown for fuel, only a small portion of the energy in the harvest turns into useful energy. The crop requires fossil fuels in the form of fertiliser to grow, and the ethanol factory needs significant inputs of energy to turn the grain starches into ethanol. Typical figures for UK wheat are shown in the chart below.
Energy value: thousand kilowatt hours per hectare*
* Please note that these are approximate figures.
The energy value of the whole crop is about 70,000 kWh per hectare. But half of the calorific value comes in the form of straw. Energy needs to be expended to get the grain to grow (fertiliser and tractor diesel) and the net value of the grain delivered to the processor is about 31,000 kWh per hectare. To turn wheat into ethanol, the grain needs to be processed and then fermented. This requires heat. The energy value of the ethanol coming out of the plant may be only 19,000 kWh per hectare. This is before the deducting the 7,000 kWh of energy that has been needed for the conversion process. In a car engine that is only 25% efficient, this converts to about 5,000 kWh of motion.
Put simply, biofuels only use part of the calorific value of the crop, need a lot of energy to process and are then burnt in a very inefficient internal combustion engine. We get 5,000 kWh of useful kinetic energy in return for spending 81,000 kWh (the energy value of the crop, the amount of heat needed to ferment the grain, and the energy used to grow the crop). This is a very bad return, made only slightly better if we include the energy value of the de-starched grain, which can be fed to cattle.
Compare this with simply taking the straw and the grain off the field and burning it to generate electricity. At a power station efficiency of 30% (admittedly quite high) we would get 20,000 kWh of electricity, many times better than for liquid fuel, and without any energy costs for processing. Turning temperate agricultural crops into liquid fuels makes little sense from the point of view of energy balance.
(Why do we stress temperate crops? Because tropical crops such as sugar cane have significantly better energy balance. It is mad to use prime East Anglian agricultural land for wheat to turn into ethanol. From an energy balance viewpoint, the same conclusion may not hold for unfertilised sugar cane grown on Brazilian savannah.)
Climate change and biofuels The previous paragraphs have looked at the poor return from using agriculture as a source for liquid fuels. Whether biofuels help reduce carbon emissions is a separate question. And please be in no doubt that this question is complex and that the answer is much disputed. Estimates of the benefit from using ethanol (from sugarbeet or wheat)or biodiesel (usually from the seed of the rape plant) vary enormously but are generally quite low. The new paper from Crutzen and colleagues suggests that there is a actually a climate change cost.
However calculated, the climate change benefit of using biofuels tends to be much lower than expected because agriculture has substantial emissions of methane and nitrous oxide as well as CO2. Methane comes from livestock and anaerobic decay. Artificial fertilisers add nitrogen to the soil (which is vital in helping photosynthesis). Nitrous oxide comes from the breakdown of nitrogen compounds, either in the field or in local watercourses.
Calculating the amount of nitrous oxide coming from agricultural soils and watercourses is difficult. We also know that the amount of fertiliser ending up as N2O varies substantially according to the weather when the fertiliser is applied. In addition, certain soil types appear to throw off more nitrous oxide than others.
Broadly speaking, the most optimistic figures suggest that 1 litre of temperate bioethanol might produce savings of about 40% over the greenhouse gas emissions of petrol or diesel. Pessimists, including senior people in the biofuels industry, think the maximum number is much lower, and may be as little as 10%.
What extra do the new studies show? Paul Crutzen won the Nobel prize for chemistry for his work on the depletion of the ozone layer. He has recently turned his attention to climate change issues. One paper looked at geo-engineering (covered in Carbon Commentary Newsletter #2). This latest work gives new – and much higher – estimates for the nitrous oxide output from agricultural processes.
Crutzen and his colleagues show that previous estimates of the amount of N2O coming from agriculture may be too low by a factor of almost three. Nitrous oxide from fertiliser use (and from the breakdown of farmyard manure) is the single most important greenhouse gas output in the biofuels process. Tripling the average amount created per tonne of grain or seed will almost certainly make bioethanol or biodiesel worse for climate change than conventional motor spirits.
The Crutzen paper makes some assumptions that are open to question. Some other academics have suggested flaws in the paper, but so far the general view is that the work is solid. If it does hold up under prolonged scrutiny –unusual in climate change debates – this paper alone should force political re-examination of the unthinking drive to increase biofuel use in the rich world.
Dr Dave Reay, an Edinburgh colleague of Keith Smith, one of Crutzen’s co-authors, published a comment on the results. He says that if the results stand up it will mean that the Bush administration’s legislative push towards the expansion of corn ethanol will add about 6% to climate change emissions from transport. We will see similar figures in Europe if the EU policy of getting 10% biofuels mixed into petrol and diesel continues.
No one pretends that the Crutzen paper is the final word on the issue. But it is yet another blow to the proponents of biofuels.
The Doornbosch and Steenblik critique for the OECD Roundtable on Sustainable Development This long paper is a devastating critique of current biofuels policy. It does not represent the official OECD position, but should surely influence policymakers towards reining back the policy of encouraging biofuels.
It has several clear findings:
- EU production of biofuels is never likely to provide a significant fraction of total motor fuel demand. The amount of land available is simply not large enough.
- Biofuels save small amounts of greenhouse gases. The other environmental impacts of using agricultural crops as sources for fuel make substitution even more unattractive.
- Biofuels grown in temperate lands are expensive. They require subsidy. The cost of saving a tonne of CO2 by growing biofuel crops may be $500. (In this edition of Carbon Commentary we look at Bjørn Lomborg’s view that the costs of damage caused by climate change are small compared to some of the policy measures implemented to reduce carbon emissions. Lomborg’s point is fully supported by the irrational support of biofuels by the EU.)
- ‘Second generation’ biofuels will use agricultural wastes as a source – not just the food. However the technologies for turning waste matter such as straw and leaves into ethanol is possibly decades away from commercial implementation.
- It may very well make sense to make ethanol from tropical crops such as sugar cane. At the moment, high import duties make Brazilian sugar ethanol an under-exploited source. But if blocs such as the EU throw open their markets it will encourage tropical countries to produce biofuels and there will be an inevitable incentive to convert forest land to agriculture. The climate change impact of deforestation would be severe.
- Biofuel production will tend to increase food prices. (The authors are slightly more tentative than I suggest, but I think their conclusions are robust.)
Likely impacts on future policy Agriculture and oil refiners support government policies on the use of agriculture to make liquid fuels. Agriculture likes biofuel crops because they have secure markets and because they help keep prices firm. The oil industry sees investment opportunities in refining crops. BP has just announced a new ethanol refinery in Hull, for example. But in the medium term the disadvantages of the rush into biofuels are utterly and unavoidably transparent. Increasing food prices, higher petrol costs, tropical deforestation and zero impact on emissions will eventually turn the tide against using temperate agriculture for liquid fuels. We have to hope it happens soon.