LCA is based on two fundamental principles. First, environmental impacts are quantified throughout the supply chain or ‘life cycle’, from raw material extraction (‘cradle’) to end-of-life of the product or service (‘grave’). Then, the impacts are quantified with respect to a functional unit, either a product quantity (one kilo, one car, etc.) or a service (hours, tonne.km, etc.). In that way, the environmental impacts of systems producing a similar function can be compared. Thus, LCA has become the worldwide standard for implementing environmental product declarations (e.g. European Product Environmental Footprint, Thailand Carbon Footprint International).

From a global perspective, it is paramount to account for the entire life cycle, so that local environmental improvements at one production stage or in one place are not merely the result of problem shifting to another stage or place. Similarly, comparison based on a common functional unit is crucial, in order to avoid problem shifting from one chain to another in order to compensate for any functional shortcoming. Finally, LCA assesses environmental performance across multiple impacts, such as climate change, acidification, ozone layer destruction, terrestrial ecotoxicity, marine or freshwater eutrophication, etc. A priori, such a multicriteria approach does not emphasize any one impact but it pinpoints the greatest impacts and their origins at certain production stages. The necessary tradeoffs and arbitrations can thus be documented.

Cropping system contribute to global warming

Since the 2000s, many studies have been published on agricultural LCA. In a review focusing on perennial crops, we analysed 70 LCA studies for raw or processed agricultural products, particularly in the case of bioenergy supply chains. In most chains, the cropping system was the main contributor to global warming, eutrophication and toxicity impacts. The major sources of emissions contributing thereto were the production and application of nitrogen fertilisers, in particular in the case of global warming and eutrophication, and pesticide and fertiliser use, as regards toxicity. Those emission sources were critical not only for the analysis of cropping systems (even for the less mechanized ones) but also in the case of  cropping systems delivering  raw material for a processed product (bioenergy, ground and packaged coffee, palm oil derivatives...).

Scientists can only deliver incomplete answers

LCA implementation poses specific problems for agricultural products because of insufficient data or scientific knowledge, which gives rise to a number of uncertainties. The main scientific challenges are, first, to define the representative system for the function under study, and second, to account for the variability of practices and of climatic and soil conditions. This is particularly true for perennial cropping systems or plantations. As highlighted by research on perennial crop LCA, agricultural practices, yields and impacts were found to change over the years, especially during immature stage and until the full production stage is reached.

Besides, the analysis of the many and highly diverse agroforestry systems planted under the tropics is a particularly complex task. Indeed, such systems are able to provide a series of different products and services, so the way emissions are allocated between products must be carefully defined. Moreover, researchers are working to improve the modelling of impact chains, by including new design parameters such as the consideration of soil carbon and albedo in climate change impact assessments, the impact of practices on functional soil biodiversity, etc.

At its current stage of development, LCA is able to identify the main sources of impact, then to target, test and prioritize improved practices. The LCA approach also highlights risks that can never be offset, such as irreversible peat oxidation or pollution transfers between impact
categories. Scientists can only deliver incomplete answer to the questions raised by the improvement of the method; nevertheless, LCA remains one of the most comprehensive and consistent method for estimating the impacts of human activities on the environment, including climate change.