There is no widely-available fuel that will effectively reduce all harmful emissions from the global shipping fleet, according to a recent study by researchers at the University of Manchester.

The industry is currently facing two challenges when it comes to its environmental footprint: complying with regulations around local air pollutants, including the 2020 fuel sulphur cap, and cutting greenhouse gas (GHG) emissions.

Both scenarios are going to require a drastic shift in fuel supply. But it’s important to note that a fuel that will satisfy sulphur limits is not necessarily low GHG.

“There is, at present, no readily available fuel option to deliver significant savings on local pollutants and greenhouse gas emissions in tandem,” says Dr Paul Gilbert, senior lecturer in climate change mitigation at the University of Manchester. “In particular, LNG is a promising option for meeting existing regulation, but it is not a low greenhouse gas emissions fuel.”

As part of the study, the researchers assessed the environmental footprints of six so-called ‘alternative’ fuels that can be used to power ships: LNG, methanol, liquid hydrogen, biodiesel, straight vegetable oil and bio-LNG.

Their impacts were measured in terms of emissions of local pollutants, such as sulphur oxides, nitrogen oxides and particulate matter, as well as emissions of greenhouse gases including carbon dioxide, methane and nitrous oxide.

To be deemed suitable for widespread adoption across the shipping industry, an alternative fuel must deliver emissions reductions over its entire lifecycle, not just during combustion in an engine.

When LNG is used as a fuel, for instance, its local pollutant emissions profile is much lower than that of heavy fuel oil. However, the issue of ‘methane slip’ during bunkering and ship operation means that LNG still produces significant greenhouse gas emissions.

The study emphasises the need to overcome barriers to exploiting the low-carbon potential of fuels, or find alternatives.

“As the urgent need to curtail greenhouse gas emissions is the more severe challenge, it is therefore important to ensure that any short-term measure doesn’t diminish the potential roll-out of low carbon fuels, in particular when taking into account the long life times of ships and fuel supply infrastructure,” Dr Gilbert says.

 “To meet the objective of reducing greenhouse gas emissions, whole life-cycle emissions need to be accounted for.”