The currently growing concerns around the world about foreign oil dependency and growing climate change, have contributed to an increasing interest in using bio-fuels as an alternative to fossil fuels such as coal, gas, and oil. The study conducted by Graeme I. Pearman (2013) demonstrates that bio-fuels and bio-sequestration can only make a minor contribution to lowering carbon levels and minimizing net emissions of carbon into the atmosphere. This is done through examining available solar radiation and observing how efficient natural and agricultural ecosystems are in converting that energy to usable biomass. The 11 countries compared in the study are Australia, Brazil, China, Japan, Republic of Korea, New Zealand, Papua New Guinea, Singapore, Sweden, United Kingdom, and United States, with a main focus on the researcher’s homeland, Australia. The objective of the study is to answer the following question: from a biophysical perspective, can using bio-fuels or bio-sequestration of carbon significantly contribute to the future of energy and the reduction of greenhouse-gas (GHG) emissions?—Christina Whalen
Pearman, G. 2013. Limits to the potential of bio-fuels and bio-sequestration of carbon. Energy Policy 59, 523-535.
The first part of the study focuses on comparing annual rates of solar radiation and respective energy consumption for each country. The results group countries into 3 groups. Group 1, Japan, Korea, and Singapore had energy consumption around 1 en dash 10% of incident (surface) radiation. Group 2, China, U.K., and U.S. had energy consumption around 0.1% and Group 3, Australia, Brazil, New Zealand, Papua New Guinea, and Sweden had energy consumption around 0.1 en dash 0.001% of incident radiation. These comparisons demonstrate the limits that deriving energy from the sun has on meeting national expectations for energy consumption. We can consume much more energy than the sun could ever provide us.
Photosynthetic efficiency is another limit to the use of bio-fuels or bio-sequestration. The pigments in the chloroplast are only activated by certain parts of the solar spectrum, leaving much of the solar radiation unutilized. In addition, more than 50% of photosynthetic products (sugars) are lost through photorespiration. The whole process is only 3.3% efficient in C3 plants and 6.7% in C4 plants.
The study then continues to examine the limitations of bio-fuels regarding energy efficiency captured from natural vegetation and from global crops. Net primary production (NPP) is how much carbon (or energy in this case) remains after the photosynthetic organism has used it for growth and other metabolic functions. In natural environments, a large portion of captured solar energy is used within the community and is vital for a functioning and healthy ecosystem. Thus, human use of this energy will no doubt have negative impacts on preexisting ecosystems. Agricultural ecosystems are constructed for the purpose of providing biomass for human consumption. The main difference between the two types of ecosystems is that a cultivated system inputs fossil fuels, which needs to be considered when accounting for the net production of energy. Comparisons within each of the countries were then made between energy captured annually as net primary production and the national solar radiation and energy consumption rates. The comparison demonstrates the inefficiency of the biochemistry involved in photosynthesis and is also influenced by temperature and water availability. The comparisons also conclude that modifying the NPP of the biosphere could be possible when global scale changes occur to temperature, rainfall, and carbon dioxide concentrations.
Photosynthesis can be more efficient in agricultural crops when there is plenty of water and fertilizer and crop management is most favorable during the peak growth rates. In the study, multiple samples were taken from various countries and locations in order to accurately compare the relative efficiencies of different cropping systems. This is called “tradable production” because the net production is calculated after discarding the roots, leaves, and stems of plants. Sugar cane and wheat crops have the potential to contribute significantly the nation’s energy demand, but have some economic and political setbacks that are not discussed in detail in the paper.
Though natural and agricultural biomass have the potential to provide energy for human use and to offset carbon emissions from fossil fuels, this study demonstrates that there are major limiting factors to this solution including the availability of solar radiation and the efficiency of photosynthesis needed to convert the energy into feedstock. Another limitation is how efficiently biomass can be converted into fuels that are appropriate for existing feedstocks, conversion systems, and applications. Solar radiation on land accounts for 1700 times the amount of energy consumed by humans, but the radiation and the energy demands are not evenly distributed geographically, so this process depends on the redistribution of energy. It also depends on how efficiently solar energy can be converted to meet the demands of humans, which is where photosynthesis becomes a limiting factor. In comparison, agricultural crops may be more efficient at converting solar radiation to a more usable form of energy, but the study demonstrates that wheat, rice, and corn crops have low efficiency rates that are similar to those of natural ecosystems. The only crop that shows a decent amount of efficiency is sugar cane.
The analysis conducted in this study is not meant to completely reject the idea of using crops and natural ecosystems as bio-fuel and bio-sequestration of carbon, but is meant to illustrate that this would require a huge amount of increase in land utilization and/or altering existing crops. Investors in these types of activities and governments seeking policy implementation need to be aware of these so-called “attractive” energy efficiency solutions.
The paper summarizes 12 criteria of assessments of issues raised by the possibility of using bio-fuels as a future energy source and for the bio-sequestration of carbon. The first issue that needs to be examined is the potential for agricultural and forestry capacity to deliver to energy demands and emissions reduction. Another one is evaluating the co-benefits or dis-benefits of developing policies about bio-fuels such as soil productivity, job creation, economic opportunities, international balance of trade, security of energy supply and so on. There also has to be enough net energy to cultivate crops for fuels, to produce fertilizer, transform the energy into chemical energy, and for transporting the subsequent fuel. Another issue to keep in mind is the continuously changing climate and its affect on which bio-fuels are appropriate. Other issues include timing, production location, strategic carbon & nitrogen budgeting, human capacity to convert the energy, competing use of land, costs of production, and social and political realities.
The conclusion of the paper does little to provide the answers to the various questions raised throughout the study, but rather implies that “we” have the knowledge to develop a system to produce bio-fuels and bio-sequestration of carbon from agricultural crops and natural ecosystems, but now we need more efficient biomass that will provide us with the tools we need to power that process.