William Gross’ Aug. 13 Maine Voices column, “EPA distorts basic science by calling CO2 ‘pollution,’ “ asserts that “All real pollutants share this same feature: The closer to 0 percent that we reduce the pollutant, the better.”

Not according to my dictionary, which defines “pollutant” as “a harmful chemical or waste material discharged into the water or atmosphere.” A chemical becomes harmful when it is present in a place that causes harm. Ozone in the stratosphere is essential for life on Earth. Ground-level ozone, on the other hand, is a pollutant long properly regulated by the Environmental Protection Agency.

Carbon dioxide, similarly, is useful in its place and harmful when out of place. CO2 is out of place in the atmosphere when its concentration varies from that which enabled human life to flourish. If there were no CO2 in the atmosphere, Earth’s surface temperature would be about minus 4 degrees F. If CO2 concentration were to rise to the optimal level for growing tomatoes, our surface temperature would be 8 degrees higher than today.

Along with that rise in temperature would come catastrophic changes in rainfall, crop productivity and sea-level rise. That’s the catastrophe the EPA is trying to prevent.

I’m sorry Mr. Gross was greeted by “stony silence” when he expressed his definition of pollution. I would have thought that he, as an engineer, would be aware of the relationship between atmospheric CO2, temperature and climate change.