The way this story develops is almost unsettling. Cleaner air was seen for decades as one of the clear benefits of environmental policy: fewer children with asthma, fewer hospital admissions on days with poor air quality, fewer smokestacks coughing sulfur into the sky. According to scientists, the same triumph might be contributing to ocean temperatures rising beyond what the models predicted. Exactly, it’s not a contradiction. It’s more akin to a bill that was supposed to arrive sooner rather than later.
The headline number from the University of Washington team led by Dr. Knut von Salzen is small enough to seem innocuous. Over the North Atlantic and Northeast Pacific, marine cloud reflectivity has decreased by about 2.8% every ten years. A two-point eight. In a stock report, this is the kind of figure you would shrug at. However, clouds perform one of the climate system’s most unappreciated functions by reflecting sunlight back into space before it ever reaches the water in these two ocean basins, which make up around one-seventh of the planet’s surface. The heat must go somewhere if you weaken that mirror even a little. It’s heading out to sea.
The mechanism itself resembles a puzzle from physics. Cloud droplets are seeded by tiny airborne particles, the same kind that were once spewed in enormous quantities by coal plants and shipping fleets. Clouds became brighter and lasted longer when there were more particles, which resulted in more droplets that were smaller and more densely packed. When the particles are removed, such as by the Clean Air Act, China’s aggressive sulfur dioxide reductions in the 2010s, and stricter shipping fuel regulations, the clouds become thinner, the drizzle occurs more quickly, and the droplets get fatter. There’s a feeling that while policymakers congratulated themselves, nature has been subtly adjusting.
It’s difficult to avoid feeling a little lightheaded as you watch this happen. The textbooks consistently mentioned the Twomey and Albrecht effects, named for the atmospheric scientists who first described them decades ago.
However, the real-world signal is now clearly visible in NASA’s CERES satellite data, something that previous Earth system models were unable to capture. Von Salzen’s team discovered that many of those models underestimated the strength of the correlation between dimmer marine clouds and fewer aerosols. This implies that we might have underestimated the actual warming.
Despite all of this, Mauna Loa continues to record its consistent upward CO2 curve. Between 2003 and 2022, the carbon continued to accumulate while the airborne particle pollution that partially obscured its heating effect was being removed. The marine heatwaves off the North Atlantic and the unsettling warm anomalies in the Pacific could be examples of recent ocean temperature spikes that are essentially a delayed unmasking. The cost of the warming had already been covered. The bill was simply obscured by the smog.
Although the researchers themselves are cautious, there is a chance that this could turn into a sort of dark irony. “We do not want to go back in time and take away the Clean Air Act,” stated the project’s other UW scientist, Sarah Doherty. Dirtier skies are not being argued for. The benefits to health are substantial and undeniable. The more nuanced argument is that we shouldn’t assume the cooling effect of pollution was free and that climate projections should take this dimming into account.
The next step is peculiar because of this uncertainty. Marine cloud brightening, which involves spraying fine sea-salt particles to seed brighter clouds—basically using salt to mimic what we used to do with sulfur—is currently being seriously investigated by some researchers. Massive unknowns regarding scale, predictability, and unintended consequences are highlighted in NOAA reviews. According to the precise wording of the field, science is still developing.
Whether near-term climate scenarios will be subtly updated to account for all of this is still up in the air. According to the study, they most likely ought to be. Reading the work gives me the impression that the planet has been more truthful with us than our models. The oceans were warming more quickly than the calculations indicated. We now know why. As always, the question is whether that clue shows up in time to make a difference.
