Michael Diamond thought we’d have to wait until at least this year to have enough data to understand how shipping restrictions aimed at curbing pollution have affected the clouds that cover the ocean. “Clouds are very variable, very thin and they’re always changing,” he said. “So you often need a lot of observations to get an idea of ​​what they’re doing.”
Nevertheless, just three years after the international maritime community made major cuts to sulfur emissions in 2020, a Florida State University cloud physicist Award-winning The paper studied cloud cover along shipping routes in the southeastern Atlantic. By analysing satellite data from before and after the regulations went into effect, Diamond found that: The clouds were thinningIn other words, while the global shipping industry reduced its emissions, it also made marine clouds a little less bright.
This change has important implications for Earth: it means less sunlight is reflected back into space, which means more warming.
The implications extend far beyond the isolated shipping lanes Diamond studied. Detected worldwide It has been several years since the International Maritime Organization adopted these rules. IMO 2020which set maximum levels of sulfur in fuel oil for all ships, container ships and cruise ships. 3.5 percent to 0.5 percent The goal is to clean the air in the port and surrounding areas, saving hundreds of thousands of lives each year.
done. Measurably low levels Ammonia and sulphur dioxide pollute the air around many ports, and the vast majority of marine fuels the organisation tests meet legal limits. But it has unintended consequences. Global warming will accelerate in the near future.
Just how much temperatures will rise is still up for debate.
“There will be a lot of papers published about reducing emissions from shipping,” said Robert Allen, an aerosol expert and climate scientist at the University of California, Riverside. “I don’t think they’ll all necessarily be making the same claims.”
Aerosols, short-lived pollutants suspended in the atmosphere, are used in climate models to Other variablesmost The common one comes from sulfur.Unlike its carbon relative, sulfur dioxide tends to cool the Earth by producing aerosols that reflect sunlight. Lighten the cloudsIf industries around the world reduced their emissions of these pollutants, the clouds would darken, the Earth would absorb more sunlight, and the land, air and water would warm even faster than before.
The announcement was made at the end of May by atmospheric scientist Tianle Yuan of NASA’s Goddard Space Flight Center. One of the first papers We used observational data and climate models to determine what this means for our planet. The results were stark and surprising.
So far, temperatures have been rising On average, about one-fifth of a degree CelsiusSince 1981, temperatures have risen by 0.25 degrees Celsius per decade, or just over 0.3 degrees Fahrenheit. Yuan’s findings suggest that the sharp decline in marine aerosols over the next decade will cause temperatures to rise by another 0.25 degrees Celsius. “Over this decade, if our calculations are correct, we expect the rate of warming to more than double,” Yuan said.
But in the scientific world, Not everyone agrees He and his collaborators were right.
Robert Allen believes that Yuan and his colleagues have gone astray. Original research (Pending peer review) And while they agree with Yuan about how the regulations affected the amount of light the Earth receives, they “reached some different conclusions.”
“We’re talking less than 0.05 degrees over the next 20 years,” Allen said. Indeed, as he and his co-authors pointed out, the range of their results is consistent with no “noticeable” impact on global temperatures. The discrepancy between the two results, Allen noted, is due to how they simulated the impact.
The fundamental difference between Allen’s and Yuan’s conclusions is one of modeling: Yuan relies on an energy balance model, which makes simplifying assumptions about the Earth to calculate the changes in temperature associated with specific climate forces; Allen, on the other hand, Earth System Modelaims to predict how changes in atmospheric composition will affect temperature and other parameters, providing a more realistic representation of the Earth’s climate.
A third study, by two Cornell researchers, also utilized an Earth system model and found results broadly consistent with Yuan’s study. The difference here can be explained, at least in part, by the number of “ensemble members” used. Simply put, each member of the ensemble represents the same model run using slightly different initial conditions, an approach that allows scientists to explore the myriad ways that even small factors can move the climate in different directions. The butterfly effectLarge ensembles will enable researchers to separate the signal from the noise and identify the real impacts of something like IMO 2020.
Model differences aside, a more modest effect seems more plausible. As both Allen and Diamond point out, if all the aerosols in the world were to suddenly disappear, Earth would At least 0.5 degrees warmer And at best, 1 degreeAlthough the 2020 IMO cut maritime sulfur emissions by about 80%, shipping Less than 10 percent Even before the regulations were adopted, global emissions of pollutants were over 1 million tonnes, meaning that even significant reductions in this area should only have limited effect.
But ultimately, with some suggesting warming will double over the decade and others pointing to only a slight increase, “the science isn’t done yet,” Allen said. As a result, the current debate has more to do with the potential dangers of clearing out aerosols than it does with the specific impacts of cleaning up ship pollution. Greenhouse gases.
No one doubts that it will reduce sulfur emissions Beneficial to public healthA study published in 2016 found that if sulfur emissions caps were enacted in 2020, Prevent at least 570,000 premature deaths Over the next five years, sulfur will become at least a short-lived greenhouse gas because it also cools the planet. methane On the other hand, cutting sulfur pollution would only speed up global warming.
Of course, reducing carbon dioxide emissions is important. But it can remain in the atmosphere for up to 1,000 years.Aerosols, on the other hand, fall out of the sky within a few weeks, so their accidental cooling effect doesn’t last long after the aerosols stop being emitted, even though atmospheric carbon continues to absorb heat. Fortunately, the greenhouse gas methane and ground-level ozone combine to warm the planet just as much as aerosols cool it, and they don’t last as long as carbon dioxide. Low-altitude ozone several weeks At best, and Methane will disappear within 10 years.
So getting rid of these pollutants along with the aerosols could potentially prevent a sudden warming, “but that’s exactly what’s happened,” Allen said. Not only has sulfur emissions from ships almost disappeared, but China has also Clean the air At pace Sooner than expectedMeanwhile, carbon emissions are It continued to swell The world is now producing a lot of aerosols. Yuan and his colleagues argue that this is causing a “termination shock” that is causing global temperatures to rise sharply, with effects other than just heat. If we were to eliminate the aerosols without reducing greenhouse gases, Exacerbating wildfire activity In the boreal forest, Slowing important ocean currentsand Affecting local weather patterns In ways that are not yet understood.
All this led to a book written by seven climate advocates and researchers. Open Letter to the International Maritime OrganizationThey call for the government to consider allowing ships to burn more polluting fuels on the high seas, far from populated areas, and to “enhance the global cooling effects of sulfur and similar aerosols without harming human or natural systems.” They also call for the government to support research and testing of technologies that would enable ships to, for example: Making salt aerosol from seawater Spraying it into the air gives you the effect of a bright cloud without the side effects of sulfur.
A spokesman for the International Maritime Organization said it welcomes reports and studies from almost anyone, but will only consider them if a member state brings up a regulation. So it remains to be seen whether the open letter will have any impact. But the document marks an early sign of the uproar that many scientists are worried about. Designing the Earth As the climate crisis deepens, its impacts are becoming more dramatic and deliberate.
These voices aside, the unintended effects of IMO 2020, not to mention climate change itself, make clear that humans have long been manipulating the atmosphere. But the arguments made by Allen, Yuan and their colleagues raise the fundamental question of how engineers can be expected to engineer precise degrees of intentional cooling when scientists can’t even agree on the precise effects of our accidental experiments.
