the amount of CO2 in the atmosphere today is the same as it was when we could first measure it.
That is absolutely false. The technology to accurately and reproducibly measure atmospheric CO2 levels was developed in the 1950s by Dave Keeling of CalTech. Continuous monitoring was initiated in March of 1958. Those data look like this:
Historical levels can be measured in several manners: direct measurement from air bubbles trapped in ice cores go back 800,000 years, looking like this:
The Keeling Curve
Or back up to 66 million years from carbon isotopes in alkenones or boron isotopes in the shells of foraminifera (from phyto- and zoo-planktons, resp)
No plant life can survive without CO2. It is not a pollutant, without it there would be no life of any kind on earth.
Are you suggesting that plant life or life in general was at risk from the pre-Industrial CO2 levels? The Earth's atmosphere contained a very steady 280 ppm CO2 level from over 6,000 years ago till the late 1700s when it began to rise from human use of fossil fuels. And, no one is suggesting we should or even could lower it further. At the moment, the pressing need is to get it stop increasing.
As to holding heat, water vapor is much more effective than CO2 at that but not one of you AGW cultists is calling for the elimination of water, are you?
Can I suggest you do some reading on this topic before further demonstrations of your ignorance? Water vapor is the most effective of the greenhouse gases (H2O, CO2, methane, nitrous oxide and the synthetic polychlorinated fluorocarbons). Being number two on that list does not make CO2 irrelevant. And, of course, humans have caused a 42% increase in atmospheric levels of that compound. The warming from the increased CO2 leads to increased water vapor in the atmosphere which adds a positive feedback to the situation, making it even warmer. The effect of increased water vapor is a major component of the climate sensitivity values determined for CO2.
Really, do some more reading.
en.wikipedia.org
