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Monte Heil (Daily Bee, Feb. 1, 2019) contends that there is no reason to worry about atmospheric CO2 reaching dangerous levels because “our atmosphere conveniently allows excessive gas pressure to escape into space.” What about the 95 percent of the marine species and 70 percent of the land vertebrate families that went extinct during the Permian Mass Extinction?

In the past 500 million years, there have been multiple mass extinction events, all of which have been associated with serious disruptions of the carbon cycle. During the Permian event, for example, it is estimated the atmospheric CO2 concentration climbed to over 1,000 ppm. (The current value is approximately 400 ppm) This high concentration of CO2, which resulted from volcanic activity, caused the Earth to warm to such an extent that life-sustaining ecological systems were severely impacted. Ocean acidification caused by the absorption of excess CO2 and decreases in oxygen concentration also appear to have been contributing factors.

Recent research indicates that, at the rate CO2 from the combustion of fossil fuels is now being pumped into the atmosphere, the Earth may experience its first human-caused mass extinction event. The current rate of increase is at least an order of magnitude greater than anytime during the last 66 million years. (Do a web search for “Earth May Be Close to ‘Threshold of Catastrophe’.”)

It would be reassuring if there were some kind of physical process that could prevent atmospheric CO2 from reaching life-threatening concentrations. Unfortunately, as the historical record shows, no such safeguard exists.

JACK DeBAUN

Sandpoint