Decarbonizing the





GHG and maritime pollution

Merchant navy is a major player of world trade :

  • 90 % of world freight transport is provided by ships
  • the number of active vessels is estimated at more than 50 000
  • it is the most economical mode of transport per km
  • it is the mode of transport with the lowest GHG emission per km

but, given its size and the distances traveled :

  • it represents 2 times CO2 emissions of the whole France
  • it is the main emitter of sulfur oxides (SOx : SO2, SO3)
  • it is a major emitter of nitrogen oxides (NOx : NO, NO2)

It is essential to find solutions to the pollution and greenhouse gases generated by the shipping industry.

Greenhouse gas (CO2)

The main greenhouse gas emitted by ships is carbon dioxide (CO2). CO2 is not considered a pollutant as it is not toxic on its own and is essential for vegetation growth. On the other hand, the excess of CO2 due to industrial activity contributes to the greenhouse effect and global warming.

The main greenhouse gases (GHGs) recognized by the Kyoto Protocol are (and there are many others ...) :

  • Carbon dioxide (CO2) : 1
  • Water vapor (H2O) : negligible
  • Methane (CH4) : 25
  • Nitrous oxide (N2O) : 298
  • Perfluorocarbure : (CnF2n+2) : env 10000
  • Hydrofluorocarbures (CnHmFp) : 100 Ó 15000
  • Sulfur hexafluoride (SF6) : 25000

The figure at the end indicates the equivalence of the greenhouse effect compared to that of carbon dioxide (CO2). The same amount of methane contributes to the greenhouse effect (global warming) 25 times more than the CO2.

NOx and SOx

Pollutants are substances that have a toxic effect on humans and the environment, and whose GHG effect is unknown, negligible or not taken into account. Many pollutants are emitted by ship engines (NOx, SOx, CO, N2O, HAV, VOC ...). The most important are grouped under the name NOx (NO or NO2) and SOx (SO2 and SO3). These two groups of pollutants are traced through the site These pollutants contribute to the acidification of the rains and oceans and are responsible for respiratory disorders and premature deaths in coastal areas.

Merchant marine emissions

Effects of greenhouse gases (GHGs)

What is GHG?

It is not our intention here to resume the theory and studies relating to GHG, literature is abundant on the Internet or on paper. The main points are however recalled below.

When the Earth receives energy from the Sun, it re-emits it as infrared (IR) radiations. A GHG is an atmospheric gas that passes energy from the Sun (mostly in the form of visible radiation) but reflects or absorbs IR radiations. GHGs are therefore "transparent" to the Sun's energy, but "opaque" to the Earth's energy, which leads to conserving the heat and increasing the temperature of the Earth.

Who invented GHGs?

Men have not invented GHGs, it is a natural phenomenon and it is beneficial for humanity. Without it, the average temperature on Earth would be -18 ░C instead of +15 ░C and the evolved life that we know would probably never have appeared. The problem comes from human activity (industry, food, transport ...) which brings an imbalance by increasing the concentration of GHGs, mainly in the form of CO2, but not only. This results in a real and measurable glogal warming of the climate, the effects of which are documented by many independent scientific organizations.

And pollutants in all this?

As for GHGs, many sites and publications abound on this subject. For merchant shipping, the major pollutants are nitrogen oxides (NOx) and sulfur oxides (SOx).

NOx come mainly from the chemical processes used in ship engines, whereas SOx are inherent in the nature of the very low-grade fuel used. NOx has a high degree of toxicity and is a major vector of the acid rain phenomenon.

SOx are irritants that affect respiratory capacity and contribute to early mortality in sensitive people (children, the elderly, asthmatics). Like NOx, SOx also contribute to the phenomenon of acid rain.

Photo, courtesy of Adrian Schwarz