The researchers carried out a life cycle assessment of current and future fuels used by the shipping companies to quantify their environmental impacts. The alternative fuels assessed in the study were LNG, methanol, liquid hydrogen, biodiesel, straight vegetable oil and bio-LNG. They measured the impacts of local pollutants (sulfur oxides, nitrogen oxides and particulate matter) and greenhouse gases (carbon dioxide, methane and nitrous oxide).

Fuels can incur the release of emissions at various stages of their life-cycle, for example during refining or transportation, or during the cultivation of the fuel if it is bio-derived. The latter may have impacts associated with cultivation, land-use change and agricultural inputs such as fertilizers. Although the upstream emissions are not attributed to the shipping sector, it is essential to ensure wider implications of fuel switches are accounted for, say the researchers. Failure to take upstream emissions into account in any sectoral assessment risks locking in carbon intensive solutions.

“In particular, LNG is a promising option for meeting existing regulation, but it is not a low greenhouse gas emissions fuel,” said Paul Gilbert, senior lecturer in climate change mitigation. “To understand the full extent of the environmental implications it is important to consider the emissions released over the full life-cycle and not just during fuel combustion. Otherwise, there is a risk of misleading the industry and policy on the true emission penalties of any alternative fuels.”

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