It is Reagan’s fault. Seriously.
Back before Reagan, environmentalists focused on actual pollutants, i.e., stuff that should not be in the environment and that kills people. The solution, of course, was more taxes and government control over the economy.
Then, largely because of Reagan, the Iron Curtain fell. It became obvious that the countries with the most government control had the worst environments. Much of the former Soviet Union and East Europe was riddled with toxic waste dumps. Meanwhile, successful capitalist countries were steadily cleaning up actual pollution from the environment. Basic Maslow’s Heirarchy of Needs. When you do not have to constantly worry about whether you can house and feed your children you can start focusing on cleaning up your environment.
So environmentalists switched their focus to carbon dioxide, a substance that not only should be in the environment, but that is vital to the continued existence of all life on Earth. Why focus on carbon dioxide? Because successful capitalist countries have much higher standards of living then communist and socialist countries and consequently generate and use much more electric power per capita. More electric power necessarily results in the production of more carbon dioxide per capita (if you ignore all of the natural sources of carbon dioxide).
The solution, of course, is more taxes and government control of the economy.