LCA is a method to quantitatively assess the influence of a product to the environment. It is one of the tools that is expected to contribute to establishing an environmentally-friendly society by, for example, inspecting the manufacturing and transport of necessary materials and energy for a product, and checking and assessing its impact on environment through the product's life cycle from production, distribution, consumption, disposal and recycling. Presently its use is spreading mainly in the manufacturing industry and we are at a stage where consumers may use LCA results as one of the factors in decision making.

With biomass, it is widely accepted that CO₂ is fixed during the growing period and that CO₂ emitted at combustion is balanced out. Therefore, the utilization of biomass is anticipated to be environment-friendly from the view point of greenhouse gas (GHG) emission control worldwide. There is a need to quantitatively assess it by using LCA and to clarify the necessary efforts for its utilization with even lower impact on the environment.

At Research Center for Life Cycle Assessment of AIST, we have promoted development of a method to locally assess the effective use of one kind of biomass, organic waste (livestock excretion, kitchen refuse, food industry leftovers, construction debris etc.), and have developed and made public a method for local optimization called "RCACAO".^[1] In collaboration with researchers of Asian countries, LCA assessment of large-scale biomass utilization is being done, and are conducting studies of sustainable biomass utilization. From these results, here is presented an example of LCA assessment of a large-scale plantation.

Thailand is the fourth largest producer of sugarcane after Brazil, India, and China, and is expected to produce and utilize ethanol in a large scale. We have done trial calculations of GHG emission of sugarcane life cycle, supposing that sugarcane is made into ethanol in Thailand, transported to Japan, upgraded in purity and mixed directly with gasoline.

With this utilization system there are many uncertainties as fluctuation of yield depending on the location and weather, variation of fertilizers, difference of transportation path depending on producing district, difference of generating efficiency using bagasse, the dregs after squeezing the raw material of ethanol. In order to quantitatively grasp these effects, we have made assessment by analyzing or supposing the distribution. We calculated the GHG emission of a life cycle which makes and uses absolute ethanol of 1 MJ. Fig. 1 shows results from using the Monte Carlo method which simulates by repeatedly using random values for uncertain data. According to these results, there is about 44 g to 78 g emission within the 95 % confidence interval. Here is reflected the uncertainty arising from the difference in yield and fertilizer usage, and as a result, there is a wide distribution.

The emission breakdown of the median value is shown in Fig.2, and the emission at the cultivation stage is large. This is due to the large influence of fertilizer production and dinitrogen monoxide (said to have 300 times as much greenhouse effect as CO₂) emissions from fields, as well as fuel consumption of machines used for cultivation. Next, the emission of transportation and dehydration processes is large. The GHG emission reduction effect (shown as negative value in Fig.2) from electric generation using bagasse left from ethanol production is also large, and with the improvement of generating efficiency and ethanol production efficiency, there may be possibilities for further increase in the amount of reduction.

According to our calculations, the GHG emission of 1 MJ gasoline from oil production, transportation, refinement is approximately 70 g/MJ. When comparing the two, even with biomass origin ethanol, the GHG emission surpassing that of fossil fuel is suggested to be possible if the cultivating conditions are bad and the utilization efficiency is low.