One of the ways is to use ice core samples, such as the Vostok ice core samples. It is just a calculation but if you were to believe it to be somewhat accurate it would show that the CO2 does not increase temperature and that the CO2 is more a reaction to the temperature changing. Also the Vostok ice core samples show that out of the 420 000 year sample for most of those years the temperature and CO2 of this planet was much. much. higher than it is today. Therefore there is nothing wrong with the planet and CO2. It helps the planet return to normal and become greener and more hospitable to life. The only thing we need to change is the countries filling our oceans and rivers with toxins and plastic, such as China, India and Africa.