A byproduct of photosynthesis is oxygen. Animals breathe in oxygen, eat food, and exhale carbon dioxide. If carbon dioxide is a pollutant, then every animal on earth is a polluter. Every organic molecule in the bodies of plants and animals contains carbon that was once in the atmosphere as carbon dioxide. There are hundreds of scientific studies to show that plant growth is enhanced by increases in atmospheric concentrations of carbon dioxide.
Plants grow larger, and more quickly, and are better able to withstand adverse conditions.
The Green Revolution that is now feeding large numbers of people on earth is partly due to increasing atmospheric carbon dioxide. Without abundant, economical sources of energy, millions of people would die and millions more would be reduced to dire poverty. It is not possible to reduce carbon dioxide emissions, much less to stabilize or reduce atmospheric carbon dioxide concentrations, without severe restrictions on the use of coal, oil, and natural gas. This means a global regime of severe energy rationing, because it is not possible to replace these essential fuel sources with technology that is currently available and affordable. The justification that is offered is a purported scientific consensus on climatic catastrophe predicted to result from projected increases in carbon dioxide.