Number one Greenhouse gas? Water. Also known as clouds. It accounts for roughly 95% of all Greenhouse Gases.
Second place is Carbon Dioxide which accounts for about 4%. Man accounts for only 3% of Carbon Dioxide production per year.
Therefore, if all man made Carbon Dioxide production stopped there would be a 0.12% drop in Greenhouse Gas production.
The Left is trying to do in the name of Environmentalism what they could never accomplish in the name of Communism.
Your number for carbon dioxide is off by a couple of decimal places. 400 parts per million = 400/1000000 = .0004*100 =.. 04%.
While researching this number I came up with an interesting fact: the amount of carbon dioxide in the atmosphere is measured at the Mauna Loa Observatory in Hawaii. Mauna Loa is an ACTIVE volcano which emits huge amounts of carbon dioxide!
If carbon dioxide holds in heat so well why isn’t it used in insulated Windows?
To quote Darth Vader “There is another...”.
Specifically, methane, which is a much stronger greenhouse gas than CO2. At least “some” current thinking is that it was the development of rice/irrigated farming that brought the last cold period to an end (rice paddy bacteria pump a lot of methane into the air).
Of course, the greens are using that datum to argue against switching from oil to fracked natural gas due to inevitable pipeline leakage.
FWIW, there is a group of Russian astrophysicists who have been predicting the onset of global cooling due to the current lack of sunspots.
That's if you only count production. If you count uptake, man accounts for almost zero uptake, whereas nature's uptake is all of nature's production and then some.