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article imageScientist — A sixth mass extinction of marine species is possible

By Karen Graham     Oct 10, 2017 in Science
If humans go on burning fossil fuels, a sixth mass marine extinction will be the inevitable result. By the year 2100, we will have added so much carbon to the world's oceans that the critical threshold will be reached.
This is the conclusion of Daniel H. Rothman, a Professor of Geophysics in the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology in Cambridge, MA. He has recently focused on the dynamics of Earth's carbon cycle and the co-evolution of life and the environment.
Professor Rothman reported in the journal Science Advances that he worked through hundreds of scientific studies to identify 31 occasions of significant change in 542 million years in the planet's carbon cycle.
As most of us have learned in school, the carbon cycle is the process in which plants draw down carbon from the atmosphere and cycle it through the animal community and back into the atmosphere.
Simple chart showing the carbon cycle on earth.
Simple chart showing the carbon cycle on earth.
earthobservatory.nasa.gov/features
Reaching the carbon threshold
Perhaps most interesting is the suggestion that even if the 197 nations that agreed to the 2015 Paris Climate Agreement, meet their targets, by 2100, humans will have added 300 billions tons of carbon to our oceans. Rothman calculates the threshold for mass extinction stands at 310 billion tons.
Depressingly, the world will be either at imminent risk or condemned to witness a "great dying" not seen since near the end of the Permian geological period when 95 percent of marine life vanished, or the more recent Cretaceous–Paleogene extinction event, which occurred about 66 million years ago. This was a large-scale mass extinction of animal and plant species in a geologically short period of time.
Mass extinctions are  by definition  harsh  but they each seem to be disastrous in their own unique ...
Mass extinctions are, by definition, harsh, but they each seem to be disastrous in their own unique way.
University of California Museum of Paleontology's Understanding Evolution
While some mass extinctions may be gradual and relatively benign, others, especially those associated with catastrophic mass extinction, are relatively abrupt and destructive, writes Rothman. To find out what set the five great extinctions in the geological record, as well as the 31 smaller extinction events, apart from each other, Rothman estimated the record of carbon preserved in the rocks from each period.
He was looking for a predictable carbon threshold at which catastrophe would be the outcome. Four of the five great extinction events laid well beyond the threshold. So Professor Rothman looked at the timescales of the extinction events to arrive at his modern-day threshold of 310 billion tons of carbon.
Orangutan numbers and distribution have declined rapidly since the middle of the 20th century  due t...
Orangutan numbers and distribution have declined rapidly since the middle of the 20th century, due to human activities. These include hunting, unsustainable and often illegal logging, mining, and conversion of forests to agriculture.
WWF
Moving into unknown territory: Sixth mass extinction event
Just as scientists say we are moving into "unknown territory" when it comes to warming oceans and thawing permafrost, Professor Rothman says that unconstrained fossil fuel combustion may have tipped the planet into "unknown territory."
"This is not saying that disaster occurs the next day. It's saying that, if left unchecked, the carbon cycle would move into a realm which would no longer be stable, and would behave in a way that would be difficult to predict. In the geologic past, this type of behavior is associated with mass extinction."
And while Rothman used mathematical calculations to predict the coming mass extinction, many scientists say we are already undergoing the "sixth mass extinction." It's a terrifying thought, especially when it is humans who are causing it.
The world is embarking on its sixth mass extinction  according to a Standford University study of ti...
The world is embarking on its sixth mass extinction, according to a Standford University study of tigers and other threatened species
Nicolas Asfouri, AFP/File
Perhaps more telling is that according to a research paper published in July, more than one-third of the 27,600 land-based mammal, bird, amphibian and reptile species in the study are shrinking in terms of their numbers and territorial range. The researchers called that an "extremely high degree of population decay."
The authors of the study, published in the Proceedings of the National Academy of Sciences wrote: "Dwindling population sizes and range shrinkages amount to a massive anthropogenic erosion of biodiversity and of the ecosystem services essential to civilization. This “biological annihilation” underlines the seriousness for humanity of Earth’s ongoing sixth mass extinction event.
More about earth system, Fossil fuels, Climate change, Carbon cycle, mass extinction
 
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