Life cycle emissions of greenhouse gases associated with microalgal
biofuels reported in peer- reviewed papers vary widely. For microalgal biodiesel, they
range from -75 g CO2eq to + 534 g CO2eq MJ-1 biodiesel. Available studies on life cycle
dealing with greenhouse gas emissions are consequential and subject to relatively large
uncertainties. Thus, the results of life cycle assessments of specific combinations of
product(s) and process(es) should be expressed as ranges rather than as one-point
values. Choices about the application of credits, system boundaries, expected
microalgal yields, allocation and the decarbonization of energy supply matter
substantially to the results of life cycle assessments. The way emissions of methane are
dealt with may also be important for estimated greenhouse gas emissions linked to
microalgal biofuel lifecycles. Substantially reducing uncertainties in the outcomes of
life cycle assessments awaits the availability of attributional life cycle assessments
which deal with well-monitored existing commercial microalgal fuel productionconsumption
chains.
Keywords: Microalgae, Biofuel, Greenhouse gas, Life cycle assessment, Credits,
System boundaries, Decarbonization, Allocation, Uncertainty, CO2, CH4, N2O.
