Researchers Track Influence Of Sulfate Emissions From Ships On Cloud Formation

Researchers from Imperial College London, University College London, and the University of Oxford have used satellite data to determine what effect sulfate aerosols from ships have on cloud formation. Historically, transoceanic ships have used heavy bunker oil — an end product of oil refining so thick it needs to be heated to make it flow to the engines it powers. Bunker oil typically has a high sulfur content. When it gets burned, sulfur molecules become part of the exhaust stream.

In the atmosphere, those sulfur molecules combine with oxygen molecules to create sulfates, and those sulfates act as tiny “seeds” that allow water vapor to coalesce around them to create clouds. In fact, ships often leave a trail of clouds behind in the sky as they cross the oceans. Those cloud trails are so common they have been given a name — ship tracks. The researchers studied satellite data of 17,000 ship tracks and compared it to GPS positioning reports from the ships themselves.

However, exactly how these aerosols impact the properties of the clouds is not precisely known. Researchers need a better understanding of how emissions affect cloud formations, which can influence climate warming, That knowledge will allow them to design more accurate climate models.

Lead researcher Dr Edward Gryspeerdt, from the Department of Physics at Imperial College London, says, “Ship tracks act like an experiment that would be impossible for us to do otherwise — we cannot inject sulfate aerosols into the atmosphere at such scale to see what happens. Instead, restrictions on the amount of ship sulfate emissions can contain provide us with a perfect experiment for determining just how important the aerosols are in cloud formation. By analyzing a huge data set of ship tracks observed from satellites, we can see that they largely disappear when restrictions are introduced, demonstrating the strong impact of aerosols.”

The restrictions he refers to are the set of regulations set to take effect in January of next year that will limit the amount of sulfur in bunker oil to a maximum of 0.5%. In some places, particularly Europe and North America, those rules are already in place. The satellite imagery these researchers relied on shows that ship tracks virtually disappear in areas where low sulfur fuel is used.

Out on the boundless ocean, no government has much of a say about what ships can and cannot do. If shipping companies want to continue burning high sulfur bunker oil, which is much less expensive than low sulfur fuel, there has been no way to stop them — until now. Maersk, the largest ocean carrier in the world, has been a leader in calling for the use of low sulfur fuels in shipping but many smaller competitors rely on the price advantage of high sulfur fuels to stay in business. This research, which has been published in the journal Geophysical Research Letters, could make it possible to track such ships. Nations then could ban any ships not in compliance from entering their ports.

Co-author Dr Tristan Smith, from UCL’s Energy Institute, says, “Currently, it is hard for regulators to know what ships are doing in the middle of the ocean. The potential for undetected non-compliance with the 2020 sulfur regulations is a real risk for shipping companies because it can create commercial advantage to those companies who do not comply. This study shows that science and technology are producing significant advancements in the transparency of shipping, and helping to reduce risks and unfairness for responsible operators.”

Ships aren’t the only source of sulfate aerosols. They also come from vehicles and factories, but their influence on clouds over land is much harder to  determine. But with ship tracks, the relationship is more straightforward, enabling researchers to tease out the links between aerosols and clouds more easily, according to Science Daily.

The research may have another useful purpose. Sulfates are often suggested as a way to cool the Earth artificially via geo-engineering. Inject large quantities of sulfates high into the atmosphere and they will block some sunlight from reaching the surface of the Earth where it can lead to higher average global temperatures. That is essentially what happened when Krakatoa erupted in 1883 and spewed enough aerosols into the air to lead to a temporary lowering of average global temperatures.

Many people think such geo-engineering schemes are based on a very rudimentary understanding about how the process might work. If the current climate crisis has taught us anything, it is that very small changes can lead to enormous alterations in our climate and we really have little knowledge about how such aerosol injections might work. More research about aerosols and the environment can only be a good thing