Clouds contaminated by ship exhaust fumes: a phenomenon that can influence local climate processes far beyond the polar region

The ArcticScientists have been repeating for years that the Arctic is warming three to four times faster than the global average. Every year, we lose about 71.000 square kilometers of Arctic summer ice, and it gets worse: as highlighted by the Intergovernmental Panel on Climate Change (IPCC) in its Special Report on the Ocean and Cryosphere in a Changing Climate, the Arctic is also losing its “multi-year” ice, the thickest and most resistant. Compared to the 1980s, over 90% of it has disappeared, replaced by thin seasonal ice that is more prone to melting in the summer.

In such a context, the increase of maritime traffic In the polar regions, there is considerable concern. The opening of a stable Arctic route will impose unprecedented anthropogenic pressure on the delicate Arctic ecosystems, including exposure to various types of pollution, including atmospheric emissions. In fact, ship exhaust gases can alter the cloud chemistry polar, with consequences that go far beyond the Arctic region.

The environmental impact of the assault on the Arctic sea routes

Open the Northern Sea Route It will require the development of supporting infrastructure, which currently does not exist, and the capacity to build heavy icebreakers, possibly nuclear-powered, a technology that currently has only one global player: Russia. Yet, maritime traffic through the Arctic is increased by 40% in the last 12 years and is expected to handle a global trade volume by 2100 higher than that of the Suez and Panama Canals.

It is not just a question of avoiding crises like the one in Hormuz, but of good old fashioned economics: according to recent studies, in fact, the Northern Sea Route and the Northwest Passage, made more easily navigable by the melting of the Arctic ice, offer a distance savings of up to 30-40% for routes between East Asia and Northern Europe compared to traditional routes. To date, however, most of the Arctic maritime traffic consists of fishing vessels and vessels intended for the extraction of local resources. But there is also concern about the more and more cruise ships which bring hundreds of tourists at a time to areas lacking the necessary social and relief infrastructure, which between 2013 and 2025 increased by 123%.

The impact of maritime traffic on one of the most delicate and important ecosystems on the planet is devastating: in addition to thenoise pollution which disturbs the echolocation of Arctic marine mammals and the increasing risk of impact with high-tonnage ships, there is concern about the possible introduction of alien species through the ballast water of vessels and the risk of oil spillCleaning up an oil spill in the Arctic is almost impossible, and heavy oil—toxic to fish, birds, and mammals—can remain trapped under the ice for decades. But there's another type of pollution that could affect the Arctic climate: ship emissions impact on the atmospheric chemistry of the polar region.

A research born from "unwanted data"

According to data from the International Council on Clean Transportation (ICCT) and the Arctic Council, between 2015 and 2019, black carbon emissions (Soot) from ships in the Arctic has increased by 85%, with effects disproportionate to those in other regions of the world. But the problem is more complex. A recent study conducted by Julia schmale e Benjamin Heutte of the EPFL, published on Environmental Research Letters, found that emissions from a single ship increased the local radiative power of clouds by up to 22 percent, meaning that clouds retained substantially more heat than under normal conditions.

The researchers discovered this phenomenon by following the trail indicated by some “unwanted” data collected on board the research vessel Polarstern, on a mission in the Arctic between 2019 and 2020. The EPFL researchers wanted to measure local natural aerosols and pollution transported from mid-latitudes to the polar regions. However, they then discovered that much of their data was contaminated by the research vessel itself. Persistent winds blowing from the same direction for much of the year had carried the Polarstern's exhaust emissions toward the sampling points:

"Sixty percent of our data was contaminated by our own ship. The ship's presence altered the atmosphere, and we measured its effect."

explains Schmale.

“Unlike the relatively clean Arctic environment, the ship's emissions produced peak concentrations 10 to 100 times higher than typical background levels,”

adds Heutte, a doctoral student at the Extreme Environment Research Laboratory. And this despite the fact that the Polarstern was powered exclusively by low-sulfur marine diesel fuel, introduced in 2020 by the regulations of the International Maritime Organization to prevent the formation of ultrafine particulate matter, metal particles and sulphates.

Ships in the Arctic and the chemistry of clouds

As the researchers point out, several studies have shown a low impact of ship emissions on clouds when using low- or ultra-low-sulfur fuel, but something different happens in the Arctic. Schmale and Heutte have measured the concentration of particles, their size distribution and the number of condensation nuclei around which cloud droplets form, integrating their data with those of other research groups:

“We used black carbon to understand pollution from the ship and other chemicals,”

explains Schmale. Other studies have shown that emissions from ships lead to an increase in the numerical concentrations of cloud droplets associated with a decrease in the average size of the droplets, causing the so-called Twomey effect, which increases the cloud's ability to reflect solar radiation (the phenomenon is easily explained: more drops, more surface area, greater ability to reflect light).

EPFL researchers measured the sensitivity of clouds to ship exhaust fumes during the summer season, the period when most ship traffic is concentrated. And the results aren't encouraging. As Schmale explains,

Polluted clouds can act like a blanket. They warm the surface more than a pristine cloud. In our case, we discovered that a polluted cloud can lead to accelerated sea ice melt. Despite using one of the cleanest fuels, with a very low sulfur concentration, we observe a significant impact. Using clean fuels is a step in the right direction, but it's not enough.

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