Worse than the brown acid.

Daniel Rothman, professor of geophysics and co-director of the Lorenz Center in MIT’s Department of Earth, Atmospheric and Planetary Sciences, has found that when the rate at which carbon dioxide enters the oceans pushes past a certain threshold — whether as the result of a sudden burst or a slow, steady influx — the Earth may respond with a runaway cascade of chemical feedbacks, leading to extreme ocean acidification that dramatically amplifies the effects of the original trigger.

That’s from the MIT press release on Rothman’s new paper, published in PNAS.

The MIT release continues:

Scientists know that when carbon dioxide from the atmosphere dissolves in seawater, it not only makes the oceans more acidic, but it also decreases the concentration of carbonate ions. When the carbonate ion concentration falls below a threshold, shells made of calcium carbonate dissolve. Organisms that make them fare poorly in such harsh conditions.

Shells, in addition to protecting marine life, provide a “ballast effect,” weighing organisms down and enabling them to sink to the ocean floor along with detrital organic carbon, effectively removing carbon dioxide from the upper ocean. But in a world of increasing carbon dioxide, fewer calcifying organisms should mean less carbon dioxide is removed.

“It’s a positive feedback,” Rothman says. “More carbon dioxide leads to more carbon dioxide. The question from a mathematical point of view is, is such a feedback enough to render the system unstable?”

To answer that question, Rothman surveyed the carbon record for the last half-billion years of Earth history, and then built a mathematical model of the carbon cycle in the upper ocean to help him analyze the current, human-driven injection of carbon dioxide into the climate system.

When he introduced carbon dioxide at greater rates, he found that once the levels crossed a critical threshold, the carbon cycle reacted with a cascade of positive feedbacks that magnified the original trigger, causing the entire system to spike, in the form of severe ocean acidification. The system did, eventually, return to equilibrium, after tens of thousands of years in today’s oceans — an indication that, despite a violent reaction, the carbon cycle will resume its steady state.

This pattern matches the geological record, Rothman found. The characteristic rate exhibited by half his database results from excitations above, but near, the threshold. Environmental disruptions associated with mass extinction are outliers — they represent excitations well beyond the threshold. At least three of those cases may be related to sustained massive volcanism.

“When you go past a threshold, you get a free kick from the system responding by itself,” Rothman explains.

I should emphasize that all this is a theoretical approach to the question. Rothman is a mathematical geologist, not a field guy, and his business is building formal representations of complicated systems to probe action in the real world that can’t be measured or experimented upon directly.

His prediction, then, is just that, a statement about the likelihood, not the certainty of a given outcome.  But that caveat doesn’t mean this is “just a theory.” Quite the reverse: because the model builds in solid and known physics, and is driven by dozens of observations in the historical record, this theory is one supported both by the math and the gold-standard of empirical measurement.

It’s scary, in other words, because it represents a rigorous attempt, using stable, well established knowledge, to depict a scary, inhospitable future:

In other words, if today’s human-induced emissions cross the threshold and continue beyond it, as Rothman predicts they soon will, the consequences may be just as severe as what the Earth experienced during its previous mass extinctions.

I should add that I know Rothman a little — my students made a short film about a lovely little piece of work he and his students did on the branching networks of ground water drainage systems.  Just i that one encounter, on a question he tackled mostly for fun, it was easy to see that he’s an impressive thinker, combining mathematical intuition with a nose for earth-science problems that can be expressed in tractable systems of equations.

That doesn’t make this work right; it does make the suggestion that there is a chance we’re close to a trigger of a runaway feedback in the oceans a prediction to take very seriously indeed.

The TL:DR of all this?  One — there’s a risk that major and on human-lifetime scale irreversible changes for the worse are either very near or already baked into the way we’ve hacked the climate system.  The need to squelch that hack, to stop pouring carbon into the atmosphere, is thus even more urgent than we thought.

A second implication amplifies that urgency:  Rothman’s math is simple (at least for him). It exposes one vulnerability, one potential feedback that could go against preserving the basic ecological support system human society depends on. But the climate system is big, incredibly complicated, and potentially hides a bunch of such triggers.

You can read this study, that is, as a case study, an example of how something seemingly well removed from direct warming issues (the physics and chemistry of the shells of microscopic ocean animals) can produce profound global effects.  So, if acid oceans haven’t terrified you enough, remember that where there’s one such hidden mechanism of major disruption, there may well be others.

As most of you know, I have a son. He’s nineteen now, and I find so much of my dread these days is bound up in my fear that I will leave him a world that is vastly more precarious than the one I inherited from my parents.

I do not have a good answer for myself on that, but it is one more reason why current politics seem to me to be life-or-death.  If we have any time left at all to keep the damage from climate change manageable, we don’t have that many years.  The longer the GOP holds power, the worse our chances become.  Go Science! is not the rallying cry that will win next year — but it’s damned important, even so.

And on that cheery note: have at it!

Images:  Joseph Wright of Derby, The Orrery, c. 1766

Albrecht Dürer, The Four Horsemen of the Apocalypse, 1498