Earth’s skin already bears the scars of the climate crisis. Fires ravage forests, hurricanes swamp coastlines, floods drown city blocks and entire species disappear. But beneath the surface layer, in the planet’s rocks, lies evidence of past catastrophes much more severe, reports Times of Israel.
Mass extinction event
Daniel Rothman, a professor of geophysics at Massachusetts Institute of Technology, believes we may be creeping toward a calamity for Earth’s life system as a whole — the planet’s sixth mass extinction event.
The staggering amount of carbon humans are pumping into the atmosphere and the oceans may soon cross a threshold that will disorder the planet’s carbon cycle and cause a cascade of disruptions we cannot fully envision, Rothman said.
Earth’s skin already bears the scars of the climate crisis. Fires ravage forests, hurricanes swamp coastlines, floods drown city blocks and entire species disappear. But beneath the surface layer, in the planet’s rocks, lies evidence of past catastrophes much more severe.
Mass extinctions leave both a marine record and a terrestrial record, but he and other researchers focus on the marine record because the data is clearer. The marine geochemical records in sedimentary rocks, and the fossil record, are more straightforward to interpret. A fossil found on land might be indicative of a specific environment, but the oceans are well-mixed, and a find is more likely to be indicative of the global environment.
Rothman said current research, which involves counting fossils and current die-offs, is factual and connected to his research but outside of his realm. Many of the current extinctions are due to land use.
He began his research into the area five or six years ago partially to address that question.
“Mass extinctions represent some type of cascade of positive feedbacks that cause a global ecosystem crash. What we’re seeing today is very serious; however, I don’t know how much is necessary to move us to the tipping point that would create a global catastrophe for the global ecosystem,” he said. “I can’t say we haven’t, I just don’t know how to say when we would.”
Testing the water
There have been many disruptions to the carbon cycle in the past that were significant for the climate but did not result in mass extinctions, however. Rothman, from MIT’s Department of Earth, Atmospheric and Planetary Sciences, investigated what made the difference, or put another way, “Why were mass extinctions special?”
Carbon is a crucial element in biological compounds, and a major component in many minerals. It enters the atmosphere as carbon dioxide when we burn fuel.
The carbon cycle is a complex, nonlinear system that centers on a loop between photosynthesis and respiration. As part of the cycle, the element is exchanged between the atmosphere and the upper levels of the ocean. Too much carbon can outpace the ocean’s “damping mechanisms” and overwhelm the cycle, leading to a cascade of positive feedback that disrupts the entire system. The perturbation can take thousands of years to even out.
Too much carbon in the ocean renders it more acidic, and inhospitable to many types of life. Four of the five past mass extinction events appear to be associated with an increased rate of carbon cycle change, and “it looks as if there’s a special rate of change which is acting as a threshold.”
Rothman concluded that, on a scale of around 10,000 years, what matters is the rate at which carbon is added to the atmosphere. But on a short time scale — a century or two — what matters is the sheer amount of carbon being injected into the skies.
2 million years of magma
Most mass extinctions do not come about with an asteroid impact and a burst of light, but take place over eons.
To the best of our knowledge, the planet’s most severe mass extinction event, the end-Permian extinction, took place around 252 million years ago.
It coincided with massive volcanism in the Siberian Traps, a vast region that burst with eruptions and spewed magma for some two million years, pumping chemicals, including carbon dioxide, into the atmosphere. Some 3 million square miles of basaltic rock carpeted today’s Russia as a result.
It began abruptly and took place over as much as 60,000 years, researchers said — a blink of an eye in geologic time.
The K-T extinction event that wiped out the dinosaurs and three quarters of plant and animal life on earth 66 million years ago was the earth’s most recent mass extinction event. It was likely tied to an asteroid impact, but also coincided with tens of thousands of years of massive volcanism in the Deccan Traps in today’s India.
Tipping points
The deep past is murky, the records incomplete, and little is known with absolute certainty. Moreover, extinctions take place on a continuum, with species dying out even when systems are stable.
Rothman said that during times of environmental stress, we have a record of carbon cycle behavior, and there is a clear association between carbon cycle change and mass extinction, but many other factors likely play a part.
He compares mass extinctions to the 2008 financial crash.
“There are what we call tipping points, or positive feedbacks in the system, and we don’t really understand them,” he said. “This is really at the vanguard of scientific research in this area.”
The scientific endeavor
Some species have gone extinct because of human greed and cruelty, others by negligence, some die off despite our best efforts, and the vast majority disappear before we know of their existence. We still don’t understand the ramifications of extinctions, or the destruction we wreak on the environment.
A large number of people around the world are trying to figure out the history of the environment and the history of life and what it might mean,” Rothman said. The endeavor will help us understand the dangers of modern climate change.
Events like the COP26 climate conference are a step in the right direction, but reaching political agreements and getting people to cooperate is still far outside our grasp.
Rothman co-founded MIT’s Lorenz Center, a “curiosity-driven” advanced climate research center, to better predict and understand the most complex scientific challenge we have faced as a species.
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Source: Times of Israel
