We’ve Been Accidentally Geoengineering the Earth for Decades with Ship Tracks

For the past few decades, the entire planet has been conducting an experiment that could save us from climate change disaster. It’s the kind of experiment that would never be allowed to happen under normal circumstances, due to how dangerous it is and how catastrophic the results could be.

In fact, we didn’t even realize we were conducting it until recently. In 2020, the United Nations International Maritime Organization (IMO) imposed a regulation requiring ships to cut down on sulfur pollution emitted by the fuel it burnt by more than 80 percent to improve air quality. A few years afterwards, scientists began studying the clouds formed from the exhaust of these vessels known as ship tracks.

What they found was a double-edged sword. While the number of ship tracks were greatly reduced (indicating that the IMO regulation was working), this also resulted in something else: the warming of the planet. It turned out that the sulfur dioxide being emitted by the ships wasn’t simply making air quality worse; it was also seeding low-lying ocean clouds—brightening them and causing them to reflect sunlight away from the planet and cool things down.

Ship tracks over the pacific ocean caused by shipping container vessels.

Ship tracks over the Pacific Ocean caused by shipping container vessels. It turned out that the sulfur dioxide being emitted by the ships wasn’t simply making air quality worse; it was also seeding low-lying ocean clouds—brightening them and causing them to reflect sunlight away from the planet and cool things down.

NASA, Terra, MODIS

“You had a reflection effect that reflected sunlight back into space and produced a cooling,” Michael Diamond, an assistant professor of meteorology and environmental science at Florida State University, told The Daily Beast. “If we look before the regulation went into effect and after, we can already see the clouds changed. They’re not brightening as much as they used to be.”

Diamond authored a paper published on July 25 in the journal Atmospheric Chemistry and Physics examining the changes in clouds over major shipping corridors in the Atlantic Ocean. He found evidence that suggests that the loss of cloud brightness resulted in a 50 percent increase of sunlight hitting the ocean surface—causing warming temperatures as a result.

These findings—along with a number of other studies conducted examining the loss of high-sulfur ship tracks over the ocean—may help bolster the case for geoengineering, a term to describe the technologies that can be used to artificially alter the Earth’s climate. While it’s a controversial and potentially dangerous strategy, proponents say that it’s rapidly becoming one of the few options we have to stave off the worst impacts of climate change.

“It’s really only natural to ask the question of should we be doing this deliberately to buy us time for decarbonization or to scale up carbon renewal technologies,” Diamond said.

While it seems like an idea torn from the pages of a sci-fi novel, the idea of blocking the sun to cool down the planet is quickly gaining favor. The White House has announced funding for a five-year research plan into geoengineering in response to a Congressional mandate developed with the National Oceanic and Atmospheric Administration.

These initiatives typically come in a variety of different forms. The most common include some form of solar radiation management (SRM), which are systems to reflect sunlight away from the Earth. We’ve seen this happen before in nature during large volcanic eruptions that throw massive clouds of debris and gasses like sulfur dioxide into the air, which block sunlight and can cause global temperatures to drop.

Similarly, the ship tracks had previously been cooling down the Earth, all while poisoning the air. Decreased ship tracks resulted in a drop in sulfur dioxide emissions, but also caused temperatures to spike.

Of course, this brings up an odd and uncomfortable question: If reducing greenhouse gasses actually warms the planet, why would we want to do so? Diamond is quick to point out that the deleterious effects of greenhouse gas emissions are far more destructive than the warming temperatures caused by the diminished ship tracks. Moreover, the benefits of getting rid of greenhouse gasses like carbon dioxide, sulfur dioxide, and methane will eventually provide a much stronger cooling effect.

“If you reduce [carbon dioxide], methane, and other aerosols, you do get a short term acceleration in warming, but that will cancel out over the longer term,” he said.

Using this idea, researchers can develop their own artificial marine cloud brightening systems to replicate the effects of ship tracks—but without toxic sulfur dioxide or other greenhouse gas emissions. One method would involve using nozzles specifically engineered to spray specifically sized seawater aerosols into the atmosphere atop ships to mimic the ship tracks. A few fleets of these vessels saturating the skies above our oceans would have a near immediate effect in cooling down our oceans.

However, the ramifications of such a measure might be severe such as accidentally causing massive rainfall in ecosystems ill-prepared for them, or causing the world to cool down too much resulting in a “Little Ice Age” scenario where crops fail causing worldwide famine.

There’s also the question of whether or not it would actually work at all—something scientists are already asking when it comes to the latest ship tracks research.

This might seem to be a clear indicator that solar geoengineering is not only a viable option, but one that we’ve already been inadvertently employing to cool our planet for decades. But experts are actually split on what the data means. Though Diamond believes that the evidence should encourage more scientists and institutions to invest more into geoengineering research efforts, he and other atmospheric scientists say it falls well short of providing any conclusive evidence that marine cloud brightening could be a panacea or even just an effective tool for our climate woes.

“There’s been some dimming—but not as much as we expected,” Duncan Watson-Parris, an atmospheric scientist at the Scripps Institution of Oceanography, told The Daily Beast. He co-authored a number of different studies in the past few years regarding the impact of ship tracks on marine cloud brightening, and has seen his beliefs on the matter evolve over the years.

A 2022 Nature study Watson-Parris helped lead used ship tracking data to analyze the clouds over where these vessels traveled to assess their impact on nearby clouds with no ship pollution. He and his team found that it resulted in the increase of cloud volume and brightened marine clouds causing a cooling effect.

But, in a preprint published May 16 in Atmospheric Chemistry and Physics, the same researchers looked at the brightening effects before and after 2020—and discovered that there actually wasn’t much of a change between the two. This shows that the clouds are “pretty much saturated,” according to Watson-Parris.

“Even by reducing 80 percent of the emissions, the clouds themselves don’t get much darker because they’ve already had plenty of aerosol,” he explained. “This leads me to think that actually, the clouds are already fairly saturated with aerosol and pollution. And therefore, the emissions reductions probably didn’t have a massive effect.”

The effects of the lessening sunlight hitting the Earth due to the IMO regulation are also difficult to quantify, according to Rob Wood, an atmospheric scientist and principal investigator for the University of Washington’s Marine Cloud Brightening Project. He noted that carbon dioxide emissions have increased over this time and have a much longer lifetime in the atmosphere than sulfur dioxide, “so comparing the effect of the IMO regulation with the increasing [carbon dioxide] is hard to do,” he told The Daily Beast.

“In addition, on timescales of a decade or less, the natural variability of the climate system tends to control the temperature fluctuations,” he added. “In short, we are going to have to wait for a few more years to determine the impact of the IMO 2020 regulation.”

So it’s still fairly early after the IMO regulation to draw any hard conclusions about its impact. While solar geoengineering experts are hopeful about the new research, they caution that it all should be taken with a grain of salt.

“Our takeaway is that reduction in aerosols from ship emissions, and in fact, all emissions, is a critical near-term climate risk that we do not understand well enough,” Kelly Wanser, co-founder and senior adviser of the Marine Cloud Brightening Project at the University of Washington, told The Daily Beast. “In particular, we have not had sufficient observational coverage to gather the data needed to understand and quantify these effects.”

Despite this, both Wood and Wanser believe that this should encourage stakeholders such as world governments and academic institutions to invest in geoengineering research. More needs to be understood before deploying—especially when the consequences of doing so could be immense.

“This is controversial,” Diamond said. “There are potential downsides to the technology like maybe changing the circulations and rainfall patterns in ways that are potentially harmful to certain communities and ecosystems.”

“We lack sufficient information about both the effectiveness and the side effect risks of marine cloud brightening to know whether to try to use marine cloud brightening, or how it might be used to maximize effectiveness and minimize risks,” Wanser said. “A great deal of research is needed.”

Like the clouds above our oceans, we want to look towards a brighter future. We just don’t want to do it at the expense of our lives—but then again, we might soon not have much of a choice.

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