Does climate change cause increase in CO2?
One reason is that we know exactly where the current increased CO2 comes from.  That is, we know from economic data how much petroleum, natural gas, &amp; coal is extracted and burned.  From that simple chemistry lets us compute the amount of CO2 produced, and we find that (after allowing for factors such as e.g. some being absorbed by the oceans) that the amount created by burning fossil fuels matches the observed increase.

(There are also more subtle measurements, such as isotope ratios, which I'm not qualified to expound in any detail...)

Another reason is that for warming to have caused the observed increase in CO2, there'd have to be some other cause for the warming.  No such cause has been found.  Suggested causes such as variation in solar output have been ruled out by measurements.