There is indeed scientific justification for the claim that carbon dioxide is responsible for the temperature rise that occurred over the last century. The atmosphere absorbs infrared light, which makes the surface of the Earth warmer than it would otherwise be; increasing the CO2 concentration will increase the absorption and thus increase temperature.
There are simple and complicated ways to study this effect. The simple ones leave out aspects of the environment; the complicated ones require supercomputers. The results are broadly consistent with each other; they all predict a warming consistent with what is observed.
Earth’s temperature has gone up two Fahrenheit degrees within my lifetime — 100 times faster than geological processes can account for. Also in my lifetime, the amount of CO2 in the atmosphere has gone up by a third. This relationship was predicted 100 years ago. The climate change theory predicted an effect that has now been observed. Scientists take such theories seriously.
The rate of temperature increase is slow but will be very difficult to stop and impossible to reverse. Instead of quibbling over details of the predictions, we should be discussing the possible consequences and how to prevent the worst effects.
Joseph P. Straley