From Watts Up With That?

By Charles Rotter

Ah, the marvel of modern climate science. For decades, we’ve been reassured that climate models are finely tuned instruments of prediction, capable of telling us what our planet will look like in a hundred years. But every so often, like a plot twist in a mediocre whodunit, we discover a brand-new “game-changing” variable. Enter methanethiol (MeSH), the newly crowned darling of aerosol cooling over the Southern Ocean.

According to a recent study published in Science Advances, MeSH—a sulfur compound previously relegated to obscurity due to its reactivity—is now recognized as a key player in climate cooling.

The discovery shows that emissions of MeSH, derived from marine biological activity, enhance the sulfate aerosol burden by up to 70% over the Southern Ocean. These aerosols scatter sunlight and cool the atmosphere, reducing the radiative bias of climate models in this region. Oh, and this isn’t a minor tweak. We’re talking about a 28% boost in the direct radiative effect of aerosols over a vast area. Oops, missed that one for decades.

Abstract

Ocean-emitted dimethyl sulfide (DMS) is a major source of climate-cooling aerosols. However, most of the marine biogenic sulfur cycling is not routed to DMS but to methanethiol (MeSH), another volatile whose reactivity has hitherto hampered measurements. Therefore, the global emissions and climate impact of MeSH remain unexplored. We compiled a database of seawater MeSH concentrations, identified their statistical predictors, and produced monthly fields of global marine MeSH emissions adding to DMS emissions. Implemented into a global chemistry-climate model, MeSH emissions increase the sulfate aerosol burden by 30 to 70% over the Southern Ocean and enhance the aerosol cooling effect while depleting atmospheric oxidants and increasing DMS lifetime and transport. Accounting for MeSH emissions reduces the radiative bias of current climate models in this climatically relevant region.

https://www.science.org/doi/10.1126/sciadv.adq2465

But let’s not get too hung up on the past. Sure, we’ve been modeling oceanic sulfur emissions for years and conveniently left MeSH out of the equation because, well, nobody thought it was important enough. Dimethyl sulfide (DMS) got all the attention. It was the prom queen of sulfur compounds while MeSH lurked in the shadows, its impact obscured by inconvenient analytical challenges. If only we had better tools earlier—or more curiosity. Instead, climate models hummed along, blissfully ignorant of this overachieving sulfur source.

The “Settled Science” Myth

This latest revelation underscores a glaring truth: the so-called “settled science” of climate prediction is about as settled as a house of cards in a windstorm. For years, we’ve been told the models are robust, the predictions reliable. Meanwhile, every few years, another critical factor—like MeSH—emerges, requiring significant recalibration, yet we’re continuously reassured of both the past accuracy and the future reliability of these models, as if such revelations are mere footnotes rather than paradigm shifts. Are these models’ approximations of reality, or are they haphazard guesses dressed up in complex mathematics?

The study’s authors painstakingly compiled global data on MeSH concentrations, feeding it into a chemistry-climate model to quantify its effects. The results? Not only does MeSH enhance aerosol cooling, but it also extends the lifetime of DMS, amplifying its cooling impact. Essentially, the climate system has been operating with a hidden double feature of sulfur-driven cooling—and we’re just now cluing in.

Why Does This Keep Happening?

Perhaps it’s time to acknowledge that climate models, while valuable, are not omniscient. They’re as much about what we don’t know as what we do. MeSH joins a long list of overlooked or misunderstood variables—like cloud microphysics, ocean circulation anomalies, and feedback loops—that fundamentally alter our understanding of Earth’s climate system.

In this case, the ramifications are clear. The additional cooling effect attributed to MeSH may mean we’ve been overestimating certain warming scenarios. Or perhaps it simply adds another layer of uncertainty to already imprecise projections. Either way, the narrative of “settled science” takes another hit.

Lessons in Humility (or Not)

To the climate science community: congratulations on this groundbreaking discovery. Truly. But let’s not pretend this is the last time something will crawl out of the data and rewrite the story. The next unconsidered variable might already be lurking, ready to wreak havoc on those supposedly “final” IPCC models.

To everyone else: remember this the next time you’re told to trust the models without question. They’re useful tools, but they’re only as good as the data and assumptions behind them. And as MeSH has shown, those assumptions have a habit of being incomplete.

So, here’s to MeSH: an unsung sulfur hero proving once again that “settled science” is more about marketing than reality. What other surprises does climate science have in store? Stay tuned. Or don’t. The climate will keep changing whether we’re ready for it or not.