Science 4 min read

Breaching the Carbon Threshold Means Mass Extinction

If we keep emitting carbon, as usual, our planet may get past a certain threshold that could trigger another mass extinction.

nevodka / Shutterstock.com

nevodka / Shutterstock.com

Earth’s long and tumultuous past has been rocked by many significant events that changed the course of history.

In the global fossil record, our planet has experienced five mass extinctions. As to what caused these cataclysmic events, there’s not a single and definite culprit to blame. But in almost all cases, scientists found evidence suggesting rapid climate change.

It took Earth millions of years to recover from each of these major extinction events, which caused millions of species to die off.

Many scientists believe that we’re heading to a sixth mass extinction event by the turn of the century if we continue our “dirty” business as usual. And a new MIT study adds weight to these warnings.

Mass Extinction Event A-Brewing: Watch for the Carbon Threshold!

Extinction risk is real, and it’s threatening humans and millions of plant and animal species.

According to Daniel Rothman, a professor of geophysics and co-director of the Lorenz Center in MIT’s Department of Earth, Atmospheric and Planetary Sciences, Earth is sending feedback, and we should pay attention.

Per Rothman’s findings, if a certain carbon threshold in the oceans is crossed, Earth could react with a “runaway cascade of chemical feedbacks.” If we keep releasing carbon dioxide into the oceans at current rates, we will get past this threshold, “whether as the result of a sudden burst or a slow, steady influx.”

With increasing carbon concentrations in seawater, pH levels decrease, while acidification — the evil twin of climate change — increases substantially.

After going through 540 million years worth of geologic records, Rothman observed a recurring pattern in Earth’s carbon cycle. He found that near the time of the fourth mass extinction event that Earth witnessed, the carbon cycle was dramatically disrupted.

In 2016, professor Rothman was awarded the Levi L. Conant Prize from the American Mathematical Society (AMS) for his work on Earth’s carbon cycle.

Previously, scientists assumed that the scope of the event depends on the changes in ocean carbon. They thought it should be proportional to the initial trigger, which means that the bigger the trigger, the bigger the environmental disruption.

However, Rothman says “It didn’t matter what initially caused the events; for roughly half the disruptions in his database, once they were set in motion, the rate at which carbon increased was essentially the same.  Their characteristic rate is likely a property of the carbon cycle itself — not the triggers because different triggers would operate at different rates.”

Earth’s Carbon Feedback

Volcanic eruptions and other large-scale disturbances take tens of thousands of years or more to excite a major carbon cycle disruption. Humans can do it in a matter of a few hundreds of years. In fact, we are doing it right now, pumping carbon into the air at a “magnitude faster than the worst case in the geologic record — the end-Permian extinction.”

“Once we’re over the threshold, how we got there may not matter,” says Rothman.“Once you get over it, you’re dealing with how the Earth works, and it goes on its own ride.”

It’s professor Rothman who, in 2017, rang the alarm bell about the sixth mass extinction mentioned above. The cascade of events triggered by ocean carbon rising levels would culminate in a mass extinction event by 2100.

In his new efforts, he developed a mathematical model to represent Earth’s carbon cycle in the upper ocean and what would be the consequences if this carbon threshold is breached. This is how Earth responds to rising ocean carbon by environmental stress that would stretch to the land.

Rothman’s model suggests that below a certain threshold, the ocean may experience mild acidification, but the carbon cycle would always return to a stable state. 

At higher rates, however, the carbon cycle would respond differently.

“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.”

Rothman will publish the results of his study this week in the journal Proceedings of the National Academy of Sciences.

Read More: Planet Human: Earth Officially Enters the Anthropocene Era

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Zayan Guedim

Trilingual poet, investigative journalist, and novelist. Zed loves tackling the big existential questions and all-things quantum.

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