1) CO2 is a greenhouse gas Nobody (that I know of) disputes this
2) CO2 levels in the atmosphere The level of CO2 in the air has risen pretty dramatically since the industrial revolution, that is, since we’re starting to burn fossil fuels on a large scale
3) Measurement wiggle room Whilst 1&2 are not in dispute, if you though greenhouse gasses in the air on an industrial scale that gets the CO2 levels up, alterning the composition of our atmosphere, it’s not idiotic to expect this will alter climate However, there is some wiggle room when we actually try to measure these effects as: Measuring ‘global’ temperature consistently over a large period of time isn’t entirely straightforward Climates are complex adaptive systems that behave in non-linear and unexpected ways That wiggle room can (and is) exploited