Neurons of human brain work on the principle of “all or none” where they throw electrical signal after surpassing a certain threshold, likewise, researchers’ team at MIT observed that cascading chemical effect on ocean water can be seen after breaking the specific threshold of Carbon dioxide in earth’s Carbon Cycle.
Daniel Rothman, professor of geophysics and co-director of the Lorenz Centre in MIT’s Department of Earth, Atmospheric and Planetary Sciences, has found that if rate at which carbon dioxide enters ocean breaks certain threshold whether a result of slow or burst, the earth may respond it with cascading chemical feedbacks such as extreme ocean acidification. Considering geologic records of over 540 Million years, it is observed that the excitation of carbon cycle had happened over 4 out of 5 mass destructions in Earth’s history.
Today’s Oceans are absorbing carbon on higher rates than past geologic records where humans are pumping carbon dioxide faster than volcanic eruption or other disturbances that caused carbon pumping in past tens of thousands of years.
“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 ride.”
It is known that carbon dioxide from the atmosphere dissolves in seawater not only makes the water acidic but also decreases the concentration of carbonate ions results in the dissolution of calcium carbonate shells. Shells effectively remove carbon dioxide from the upper ocean by weighing organisms down and enabling them to sink to the ocean floor along with detrital organic carbon.
Rothman captured his view “More carbon dioxide leads to more carbon dioxide” with the help of his new mathematical model which comprises two differential equations that describe interactions between the various chemical constituents in the upper ocean and observed how the model responded as he pumped additional carbon dioxide into the system, at different rates and amounts.
He observed that the addition of carbon dioxide at a modest level in an already stable system, upper Ocean will cause transient acidification and will go back to a healthy state. However, when he added carbons at higher rates near thresholds, he found that carbon cycle reacted with a cascade of positive feedback by causing the entire system to a spike in the form of severe acidification yet resume to a healthy state. Environmental disruptions associated with mass destructions are outliers where excitations are well beyond thresholds.
“When you go past a threshold, you get a free kick from the system responding by itself,” Rothman explains. “The system is on an inexorable rise. This is what excitability is, and how a neuron works too.”
Rothman’s model predicts that the two effects cancel: faster rates bring us closer to the threshold, but shorter durations moves us away and considering threshold, the modern world is in roughly the same place it was during more extended periods of massive volcanism.
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.
The study is published in the journal Proceedings of the National Academy of Sciences.