“ but the most present greenhouse gas is carbon dioxide.”
The most present Greenhouse gas is water vapour which is about 100 time more plentiful in the atmosphere than Carbon Dioxide and far more potent in its greenhouse effect (as confirmed by NASA here and The American Chemical Society here). Both gases are essential to life on earth, as is Ozone. Without Ozone UV radiation from the sun would destroy all carbon based life forms (i.e. fungi & bacteria, plants, insects, animals, us,) without water vapour the vast differences between daytime and night time temperatures would destroy plant life and the food chain would break down and without carbon dioxide, from which plants extract carbon to make leaves, stalks, fruit, seeds during daylight hours in a process called photosynthesis, the food chain would again break down.
At 400 parts per million Carbon Dioxide is a trace gas in the atmosphere and far more is emitted by plants that by human activity. During the hours of darkness photosynthesis cannot take place (photo is the Greek word for light,) and plants absorb Oxygen and emit Carbon Dioxide.
In the distant past Carbon Dioxide levels have been far higher than they are now, in fact at the height of the Ordovician ice age 450 million years ago ice core samples have shown CO2 levels were hundreds of times higher than they are now. However, during some other ice ages, CO2 levels were only slightly higher or around the same. Which suggests CO2 is not the main player in the greenhouse gas effect. This should not be surprising as the frequency filtering effect of CO2 only duplicates a small part of that done by water vapour.