it has been revealed that the carbon footprint of the much-anticipated “green” ferry, MV Glen Sannox, will be significantly larger than that of the 31-year-old diesel-powered ship it is set to replace on the route between the Scottish mainland and the Isle of Arran.
CalMac’s emissions analysis shows that the dual-fuel Glen Sannox will emit 10,391 equivalent tonnes of CO2 annually, compared to 7,732 tonnes for MV Caledonian Isles. While the new vessel boasts greater car capacity, its larger engines contribute to the increased emissions, as does the use of liquefied natural gas (LNG), which emits methane—a greenhouse gas with a much greater global warming potential than CO2.
Ferries procurement agency CMAL, which owns the vessel, argued that the comparison was “inaccurate,” stating that Glen Sannox is a larger ship. However, experts have raised concerns over the climate-friendliness of LNG.
Professor Tristan Smith, a transport emissions expert from University College London’s Energy Institute, told the BBC: “In a best-case scenario there’s a negligible benefit of using LNG, and at worst there would be a deterioration.” He added that when the “upstream” carbon costs of importing LNG from places like Qatar are taken into account, running the new ferry on diesel might be the more environmentally sustainable option.
Background on Glen Sannox
The Glen Sannox is the first UK-built ferry capable of running on both LNG and marine gas oil (MGO), a type of low-sulphur diesel. When it was launched in 2017, then-First Minister Nicola Sturgeon heralded it as a step forward for Scotland’s “world-leading climate change goals.”
However, the complexity of incorporating LNG technology caused significant delays and cost overruns at the Ferguson Marine shipyard. The vessel was only delivered last month, years behind schedule and significantly over budget.
The size of the ferry also presents logistical challenges, as it cannot dock at Ardrossan, the usual mainland harbour, until major redevelopment work is completed.
Despite these challenges, the Glen Sannox brings certain benefits when it enters service next month. It can carry 127 cars compared to the Caledonian Isles’ capacity of about 90, and it is expected to reduce air pollutants such as NOx and SOx. Its increased power and manoeuvrability are also likely to result in fewer weather-related cancellations.
Carbon Emissions Analysis
According to the emissions data obtained by the BBC, the greenhouse gas emissions benefits of using LNG over MGO are minimal. The analysis shows that the Glen Sannox produces 11,375 equivalent tonnes of CO2 annually when running on MGO, compared to 10,391 tonnes on LNG—a reduction of less than 9%.
However, the increased size and fuel consumption of the Glen Sannox mean its overall carbon footprint is about 35% larger than the Caledonian Isles, which is scheduled to return to service in March after undergoing repairs.
Why Are Emissions So High?
The higher emissions are not a result of design or construction flaws by Ferguson Marine. Instead, they stem from decisions made by CMAL, ferry operator CalMac, and Transport Scotland during the planning and procurement process.
While the Caledonian Isles was originally designed to carry 110 cars, the increasing width of modern vehicles has reduced its capacity to around 90. This constraint, along with the push for a “green” solution, led to the larger and more complex Glen Sannox.
Nevertheless, questions remain about whether the choice of LNG as a fuel aligns with Scotland’s environmental ambitions, especially when considering its broader impact on global greenhouse gas emissions.