Methane limits to shipping - a climate action that could be done immediately

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Tiistai 9.11.2021 klo 16:36 - Mikko Nikinmaa

The low pressure dual fuel engines used in most LNG-fuelled ships are more or less the same as the two-stroke engines (Otto motors) of old Wartburgs and Trabants, or present-day lawn mowers and leaf blowers. Typical for all two-stroke engines is that a lot of unburnt fuel is emitted to the environment. For example, 8-hour use of a leaf blower emits about the same amount of hydrocarbons in the environment as driving a car around the world. Thus, it is no surprise that the use of low-pressure dual fuel LNG engines cause a massive increase in the emission of the very powerful greenhouse gas methane.

What is worrying, though, is that the governmental response has been that even though the negative climate effects of most LNG-fuelled ships are clear, it does not pay to set emission limits to methane in ships for two reasons. First, LNG is only a transition-phase fuel from diesel oil to hydrogen or ammonia. Second, acceptance of the limit in International Maritime Organization would take up to ten years, and even then the requirement could be enforced only for new motors/ships. Consequently, any climate effect would not be seen before 20-30 years have passed.

The situation is somewhat funny, since the most important reason for replacing diesel fuel by LNG was to decrease air pollution. Compared to diesel oil, LNG causes virtually no sulphur oxide emissions and decreases nitrogen oxide emissions drastically. The latter is actually the reason for the use of low pressure dual fuel engines: the alternative LNG-fuelled engines, high pressure dual fuel engines have higher nitrogen oxide emissions, and would require external catalytic converters for removing the nitrogen oxides like cars have. Since nitrogen oxides have emission limits, decreasing their emissions has been priority in ship building.

However, the inability of governments to do anything not only with regard to this but in general in combatting climate change is alarming. In the case of shipping, this can mean that the climate effects double if LNG becomes a major fuel. The major problem is that any climate actions should be done immediately, but most responses require 20 years or more with devastating results.


Avainsanat: climate change, fossil fuels, diesel oil, shipping

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