Tying past mass extinctions with low atmospheric CO2 is false

Newswise — Attempts to discredit human-caused climate change by touting graphs of prehistoric atmospheric carbon dioxide and temperature changes are not something new. Peter Clack, an out-spoken climate change skeptic has once again tried to make a point that current atmospheric carbon dioxide levels are comparatively low compared to past eras. In this recent tweet, shared by thousands, Clack includes a graph from the work of Chris Scotese, an American geologist and paleogeographer, which shows that current levels of atmospheric carbon dioxide are relatively low compared to past events and that the only other time CO2 levels were this low was during the early Permian geological era, which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago, to the beginning of the Triassic Period 251.9 million years ago. Clack mentions the “greatest extinction event in world history,” also known as the Permian Extinction as if this happened despite the low atmospheric CO2 recorded. However, most geological scientists contend that the Permian extinction occurred over the course of 15 million years during the latter part of the Permian Period (299 million to 252 million years ago).* Does this at all negate human-caused climate change that is happening in our own era? Of course not. In fact, this observation only backs the belief that a rise in global temperatures (and a sharp rise in CO2) impacts the living species on the planet. The main difference is that today’s fast rise in global temperatures can be prevented by the de-escalation of greenhouse gas emissions.

The Permian extinction was characterized by the elimination of about 90 percent of the species on Earth. Although the exact cause of the mass extinction event has been debated in the past, a recent study from 2018 showed that the Permian mass extinction in the oceans was most likely caused by global warming that left animals unable to breathe. In fact, there was a steep rise of carbon dioxide in the atmosphere during the late Permian era, as the Scotese graph shows. Scientists believe that this was caused by considerable volcanic activity in present-day Siberia (tied to the dismantling of the supercontinent of Pangaea). This event points to rising CO2 and temperatures drastically affecting the biosphere.

Chris Cramer, chief research officer at Underwriters Laboratories explains…

The first and second graphs in this Tweet show that the first claim (600 million year minimum) and second claim (lowest global temperatures) are demonstrably false.

Any relationship between the Permian extinction event and a local minimum in CO2 (relative to prior higher levels) simply shows how catastrophic it can be to living organisms when there is a significant change in CO2 levels, and associated temperatures, just as is happening right now with human activity driving CO2 above 400 ppm for the first time in millennia.

Andrew Dessler, director of Texas Center for Climate Studies and professor of atmospheric sciences at Texas A&M also chimes in…

So what's wrong with this claim?  It suggests that low CO2 is the cause of the extinction.  I am not an expert on this, but I think the extinction has actually been linked to extensive volcanism that was occurring at about that same time.  In addition, 250 years ago the Earth had 280 ppm of CO2 in the atmosphere and the biosphere was doing just fine.  In fact, during the ice age (20,000 years ago), atmospheric CO2 was 180 ppm and the biosphere did OK.

*https://www.britannica.com/science/Permian-extinction/Alteration-of-the-carbon-cycle\

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