Study: Reduced sulphur content in shipping fuel caused ‘nearly 80%’ of recent atmospheric warming

Due to a 2020 shipping regulation…’The net planetary heat uptake has increased by 0.25 Wm−2 since 2020, making the 0.2 Wm−2 due to IMO2020 nearly 80% of the total increase.’ The study also says: ‘The 2023 record warmth is within the ranges of our expected trajectory. The magnitude of IMO2020 induced warming means that the observed strong warming in 2023 will be a new norm in the 2020 s.’ — Two general comments to make here: (1) cloud physics is admitted to be not well understood, and (2) could night-time clear(er) skies mean (more) cooling, in theory at least?
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An 80% reduction in sulphur dioxide shipping emissions observed in early 2020 could be associated with substantial atmospheric warming over some ocean regions, according to a modelling study published in Communications Earth & Environment.

The sudden decline in emissions was a result of the introduction of the International Maritime Organization’s 2020 regulation (IMO 2020), which reduced the maximum sulphur content allowed in shipping fuel from 3.5% to 0.5% to help reduce air pollution, says EurekAlert.

Fuel oil used for large ships has a significantly higher percentage content of sulphur than fuels used in other vehicles. Burning this fuel produces sulphur dioxide, which reacts with water vapour in the atmosphere to produce sulphate aerosols.

These aerosols cool the Earth’s surface in two ways: by directly reflecting sunlight back to space [Talkshop comment – daytime effect only]; and by affecting cloud cover.

Increasing the number of aerosols increases the number of water droplets that form whilst reducing their size, both increasing the cloud coverage and forming brighter clouds which reflect more sunlight back to space.

Marine cloud brightening is a form of geoengineering where marine clouds are deliberately seeded with aerosols to achieve this effect.

Tianle Yuan and colleagues calculated the effect of IMO 2020 on the atmospheric levels of sulphate aerosols over the ocean and how this affected cloud composition. They found substantial reductions in both the levels of atmospheric aerosols and the cloud droplet number density.

The greatest modelled aerosol reductions were in the North Atlantic, the Caribbean Sea, and the South China Sea — the regions with the busiest shipping lanes.

The authors then estimated the effect of IMO 2020 on Earth’s energy budget (the difference between the energy received from the Sun and the energy radiated from the Earth) since 2020. They calculated that the estimated effect is equivalent to 80% of the observed increase in the heat energy retained on Earth over that period.

Full article here.