Earth Has Seen A Carbon Spike Like This Before. It Did Not End Well.
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The principle isn’t just that increasing carbon dioxide makes things get hot, but that fast changes in ocean and atmospheric chemistry can trigger a reordering of the living world. That in turn causes more chemical changes, leading to cascading changes in the biosphere. In the end-Permian, there was a collapse of plankton and fish and an explosion of bacteria that emit sulfur compounds and possibly others that exhale heat-trapping methane. Seth Burgess, a United States Geological Survey geologist who studies the end-Permian, said there are two intriguing puzzles — the trigger mechanism and the kill mechanism. There’s a general agreement that the trigger was, in part, volcanic activity giving rise to an igneous formation called the Siberian Traps. But the eruptions alone couldn’t have released enough greenhouse gases to cause the estimated 10-15 degree Celsius rise in global temperature.
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Rothman looked at 31 periods when atmospheric carbon rose, most of which didn’t have a big effect on the biosphere. When changes were big but happened slowly, life had a chance to adjust. If they happened fast but amounted to only a small carbon increase, life could go on as before. Last year, Rothman came up with a formula based on both the rate and total amount of added carbon, and demonstrated that it predicted which of those 31 periods would lead to catastrophe. According to his formula, our current rate of emissions is extremely high, but it won’t cause a mass extinction unless our total emissions add 310 gigatons of carbon to the oceans. He published the results in Science Advances.
The UN’s Intergovernmental Panel on Climate Change estimates that human activity will add 300 and 500 gigatons of carbon dioxide to the oceans by the end of the 21st century, so 310 is close to the best-case scenario. When I talked to Rothman, he said to keep in mind the uncertainty. “By looking at the geochemical record, it would appear we are going to put the system on a track toward some type of instability,” he said. “But how that works is highly speculative.”
People talk about climate change being settled science, he said, but that refers to the most basic parts. Scientists know approximately how much our emissions are likely to warm the planet — a factor called the climate sensitivity. What we don’t know, he said, is how this linear relationship might break down. “The big unknown unknowns are the positive feedbacks,” he said. “The big risk is the system takes off on its own.”
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https://www.bloomberg.com/opinion/articles/2018-12-21/lessons-on-global-warming-from-prehistoric-end-permian-extinction
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