Lower emissions from shipping could lead to higher global temperatures

The products we depend on and use every day arrive at ports around the world via giant container ships. But the shipping industry is also responsible for polluting the air and oceans with sulfur dioxide, which can negatively impact human health, cause ocean acidification, and oxidize to form sulfate aerosols.

International shipping lanes have historically accounted for 13% of global anthropogenic sulfur dioxide emissions. In 2020, the International Maritime Organization (IMO) issued stricter regulations for large ships that have led to an 8.5-megatonne reduction in annual sulfur dioxide emissions.

But such a reduction could actually warm the planet—scientists disagree on how much. Sulfate aerosols act as cloud condensation nuclei. An excess of these particles leads to brighter clouds, which reflect more sunlight back into space and can help cool the planet. Lower anthropogenic aerosol emissions could reduce this cooling effect.

Since the introduction of the IMO 2020 regulations, the planet has experienced an accelerated rate of warming. In his article published in The Future of EarthG. Jordan and M. Henry used the UK Earth system model UKESM1 to investigate possible links between global warming and the IMO 2020 regulations. Their findings showed that the restrictions had a small but noticeable effect on the climate.

The scientists used two sets of climate model simulations — one with fixed sea surface temperatures and the other simulating atmosphere-ocean coupling.

Simulations of constant sea surface temperature showed a small increase in the Earth’s radiative imbalance, mainly due to a reduction in the cloud brightening effect of aerosols. Coupled atmosphere-ocean simulations showed more noticeable changes in cloud droplet properties, especially over the North Atlantic and North Pacific, where shipping traffic is high.

Simulations indicate that the IMO 2020 regulations will increase the global annual surface temperature by just under 0.05°C – equivalent to 2 to 3 years of global warming – between 2020 and 2029.

The IMO 2020 regulations may have been one factor in the extreme temperatures that will hit the planet in 2023, but they are far from the only cause, the authors write. Regardless, they add that the potential effects of such regulations should be considered in climate change mitigation efforts.

This story is reprinted courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.