[defrost]

The cause of increasing mean tempretures is well known, it's due to the increase in the insulating properties of the atmosphere, primarily (at the moment) from increased CO2 (along with water vapor, methane, other smaller changes).

We know the makeup of the atmosphere has changed from having "libraries" of atmospheric samples.

The source of increased CO2 is also known, we humans through industrial activity have mined many many billions of tonnes of fossil fuels (coal, oil) and released an excess of that gas into the atmosphere.

This is a change that is distinctly over and above natural variations in atmospheric makeup.