09/26/2013 - 05:31

What biofuels can do

Over the last three decades, the amount of land devoted to food crops has increased at a very modest rate, but worldwide food production has expanded significantly. The UN Food and Agriculture Organization expects that patterns will be similar over the coming decades: Food demand through 2050 will increase at a rate of 1.1 percent a year, but this increased demand will mainly be met through productivity gains, with only a small expansion in cropland required. If productivity gains come in below expectations, there are large amounts of land available that could be used for crop expansion. Availability of land is not a major obstacle to the expansion of bioenergy production.

But climate change may have a negative impact on biomass productivity (that is, on production of agricultural crops and bioenergy feedstock) due both to higher temperatures and to reduced water availability. Some argue that the effects of these changes could be especially severe in the developing world. Today's temperatures in tropical areas, according to this argument, are very near the optimum for growing tropical crops, and higher temperatures would seriously harm productivity. Temperate regions, on the other hand, might actually experience higher yields along with higher temperatures. Since much of the developing world is located in the tropics, the effect of higher temperatures would be especially severe in poorer countries. But one must tread carefully here. If average temperatures increase 2 degrees Celsius or more, it is certain that the environment will change in many ways—but predicting with accuracy how specific regions will be affected is very difficult. It is not so easy to conclude that decreases in agricultural production would be most pronounced in developing countries.

Nevertheless, if one assumes that higher average temperatures around the world will affect biomass production negatively, the question then becomes to what extent bioenergy can mitigate climate change. Bioenergy can be produced in good ways or bad ways. But if environmentally friendly technologies are used and proper policies are in place, evidence suggests that bioenergy can significantly reduce emissions of greenhouse gases and meaningfully mitigate the negative impacts of climate change.

My colleague Sergio Pacca and I have calculated that 70 million hectares of sugarcane planted worldwide could—by 2030, when the world car fleet will amount to 1.6 billion vehicles—replace all gasoline and diesel used in cars and trucks (as long as the vehicles are of the plug-in hybrid variety). Sugarcane could also generate the electricity that these hybrid vehicles would consume. A huge amount of carbon dioxide emissions could be avoided this way.

Some experts believe that, without heavy reliance on bioenergy, it will be impossible to keep planetary warming below 2 degrees, but that if bioenergy is used properly, and other mitigation options are also pursued, the 2-degree threshold might not be crossed (in which case climate change would cause no serious problems for food supply). Several studies have determined that, if fossil fuel use does not decline quickly enough to limit warming to 2 degrees or less, it may be necessary to combine bioenergy with carbon capture and storage in order to bring down concentrations of greenhouse gases. This might mean that greenhouse gases would be removed from the atmosphere through the growth of crops, with the crops then burned to produce energy and the resulting carbon captured and stored. But biofuels could be an important part of this approach as well.

To begin with, biofuels made from certain feedstocks—mainly sugarcane, but also corn, animal grease, and properly planted palm oil—produce carbon emissions lower than those for gasoline and diesel over their full life cycle. Bringing carbon capture and storage into the picture might in some cases result in negative emissions. This may be the case with sugar fermentation, a process necessary for producing ethanol from sugar, starch, or even cellulosic material. During fermentation, glucose is essentially split into two products: ethanol and carbon dioxide. The carbon dioxide is typically vented into the atmosphere. But with no further treatment, this very pure carbon dioxide stream could be sent underground into saline aquifers or empty gas or oil reservoirs. This would be one of the least expensive ways to carry out carbon capture and storage, as virtually the only action required is storage. This technology is being pioneered in Decatur, Illinois, and another project in Brazil has received approval from the Global Environmental Facility. Combining biofuels with carbon capture and storage is one of the very few technologies that can remove carbon from the atmosphere and bring carbon concentrations down.

But how much climate mitigation could already have been achieved if nations had begun pursuing bioenergy on a large scale as long ago as 1980? (At that time, examples of good bioenergy projects already existed, and it was around then that publics began to learn about the possibility of climate change.) My calculations suggest that by 2015 it would have been possible, through expansion of sugarcane-based biofuels alone, to cut annual carbon emissions by nearly 9 percent. Nothing can be done today about decisions made in 1980. But in the years to come, I believe that bioenergy must be a major strategy if temperatures are to be prevented from reaching truly dangerous levels.