I don't get this concern for Earth itself. The planet had much higher CO2 levels before life began. Then plants etc. absorbed some of that CO2, and a lot of it

I don't get this concern for Earth itself. The planet had much higher CO2 levels before life began. Then plants etc. absorbed some of that CO2, and a lot of it is now in coal, oil, etc. instead of in the air as CO2. When we are burning fuels, we are actually returning the atmosphere to a more original state. However that state is not good for us. So when we are talking about global warming, it is today's life, including us humans, that will suffer, not the planet itself.