CO2 concentration in the atmosphere increases. It takes more and more to add less and less temperature. That is because all the significant increase in temp is taken up by natural sources like plant and animal life or geologic leaks or volcanoes. By the time you add our puny industrial emissions there is little or no effect anymore. The effect is logarithmic and not linear as most people think it is and as most warmists want you to think. It's simpler to understand that way but wrong. As much energy as the sun sends to earth it is still a finite amount. The narrow IR range of energy reflected back into the atmosphere--the source of CO2 warming--is mostly converted by naturally occurring CO2. There's very little left to convert so it takes more and more to find less and less in a manner of speaking. Temperature fluctuations are influenced more by cloud cover.
https://wattsupwiththat.com/2014/08/10/the-diminishing-influence-of-increasing-carbon-dioxide-on-temperature/