Thanks to the contributor who expressed amazement that a mere 400 parts per million (ppm) of carbon dioxide (CO2) in the atmosphere might have any effect on global climate. Welcome to the revelations of chemistry, where mini amounts have major effects, like yeast in dough.
Besides the greenhouse gas, CO2, burning fossil fuel also produces the odourless, colourless, lethal killer known as carbon monoxide (CO). It is considered an acute danger to human health in concentrations as low as 100 ppm. CO detectors are recommended in every home. At 400 ppm, an alarm will sound within minutes.
Chlorine used to purify water must be less than three ppm before swimming is recommended in a treated pool. The Occupational Health and Safety Administration of the U.S. Department of Labor restricts human exposure to chlorine dioxide at levels of 0.1 ppm.
Nitrogen dioxide, sulfur dioxide and ozone are measured in parts per billion to report air pollution levels for the Alberta air quality health index. The World Health Organization estimates that 2.4 million people die annually from air pollutants, measured in parts per billion. A 2005 B.C. Cancer Foundation study estimated that a mere one per cent reduction of air pollution in Metro Vancouver would save $29 million in health related costs.
Four hundred ppm in the atmosphere is huge. It can have lethal and costly implications. The UN Panel on Climate Change is warning governments to consider 400 ppm CO2 seriously. The IPCC is our detector of climate emergency and they have sounded the alarm.