2023-08-15 19:00:08
A container ship leaves the port of Lianyungang, China, July 16, 2023. AFP
Has the depollution of fuel from merchant ships and cruise ships fueled the scorching temperatures recorded in the oceans? Review Science asks the question, at the beginning of August, in a synthesis of recent research articles on the climate impact of the new regulations greatly lowering the maximum sulfur content of fuel oil used by boats. This standard, implemented by the International Maritime Organization (IMO) since January 1, 2020, makes it possible to reduce emissions of fine particles, to the benefit of human health and ecosystems, but it has an impact on the formation and reflectivity of low altitude clouds, which reflect part of the solar radiation.
The mechanism is known: the presence of sulfur in the fuel produces, during its combustion, sulfur oxides, which are converted into fine particles in the atmosphere. “These particles then act as ‘condensation nuclei’ on which water vapor is depositedexplains climatologist Olivier Boucher, researcher at the CNRS. This mechanism contributes to the formation of clouds in which the droplets are smaller and more numerous, and which reflect more solar radiation. » And thus contributes to “cooling” the climate.
If the question is attracting attention today, it is because several regions of the ocean are experiencing an unprecedented heat wave this summer. In particular, the surface temperatures of the North Atlantic exceeded their previous record by almost 1°C at the end of July. The major causes of this phenomenon are anthropogenic warming, which continues at full speed, and a particular weather situation, marked by unusually weak winds.
“Very uncertain link”
“Some air pollution control actions may also be linked to high temperatures in the North Atlantic, Pacific and Antarctica”estimates, in a press release, the British National Center for Atmospheric Science, which recalls that the change in regulations on fuels for boats “could contribute to warming sea surface temperatures, although the strength of this link is highly uncertain”.
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In study published on July 25 by the journal Atmospheric Chemistry and Physics, Florida State University climatologist Michael Diamond estimates the radiative forcing – the “warming” effect – of the new IMO regulations at around 0.1 watts per square meter (W/m2) , averaged over the entire planet. A significant assessment, although much lower than the 2.7 W/m2 of anthropogenic radiative forcing from all human activities since the pre-industrial era, according to the latest report from the Intergovernmental Panel on Climate Change. “The effect observed on the formation of clouds in the shipping lanes seems quite real, but it is very difficult, as it stands, to quantify its importance with precision.believes Mr. Boucher. The rating of 0.1 W/m2 is based on the highest assumptions. »
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