Global warming, if it is occurring, is not happening because of increased levels of carbon dioxide in the atmosphere.
The system that heats and cools our planet is complicated, involving innumerable factors - the sun, the lack of sun, atmospheric gases, ocean currents, ocean to atmosphere gaseous interactions (dissolution, releasing), vegetation levels and types, human activity, etc.
However like any multi-factorial system, the cause of any problem is usually the simplest and most obvious. For example, if you go to the doctor with a sore throat, you don't expect the doctor to start checking the functioning of your kidneys by taking a urine sample. No, instead he looks at your throat, checks your temperature and most likely concludes your throat has an infection.
Similarly if a car suddenly starts dragging to one side and makes an unpleasant grinding noise from the wheels, you don't lift the bonnet and check the functioning of the throttle cable. No, you go straight to the wheels and note that you have a puncture.
So it is with global warming. Where does the planet's heat come from? Well, by and large, from the sun of course. OK then maybe we should look at the sun. What happens when the sun goes away e.g. at night. Well the temperature typically drops in the UK by 10 to 15 C over the course of 6 hours. That is a cooling rate of almost 2C per hour. Or to put it another way, when the sun rises, the exact opposite happens; the daily temperature rises by as much as 2C per hour.
Think about that. The sun can make the global temperature rise by 2C per hour. So why on earth are we thinking that it is carbon dioxide that is making the temperature rise by 2C in fifty years? That is a rate of increase half a million times (!) less than the daily temperature rate of increase when the sun rises every morning.
Isn't it far more likely that if the global temperature is rising at a rate of 2C over 50 years that it might just be the fact that the sun has increased it's output by a tiny incremental amount? In fact isn't it highly likely, almost certain in fact, that the suns output varies naturally by a small amount, as most environmental factors do in nature?
The Earth's history clearly indicates that global temperatures have varied widely over the lifetime of the Earth, sometime much hotter, sometimes much colder (e.g. Ice Ages).
In conclusion, if the Earth is warming at a rate of 2C in 50 years, this is caused by the Sun's output increasing naturally by a tiny amount relative to its average output.
Not carbon dioxide.