1) Carbon Dioxide is a greenhouse gas - I challenge you to find a single scientist who disputes this.
2) The concentration of carbon dioxide in our atmosphere has more than doubled since the start of the industrial revolution - Ice cores allow for this to be measured with great precision for thousands of years. I challenge you to find a single scientist who believes this is from some natural process and not man-made.
3) The concentration continues to increase right this second - Measurements on Mauna Loa confirm this every time they are made
4) Carbon Dioxide is very persistent in the atmosphere, it takes up to 200 years for it to be removed via natural processes.
Any reasonable person would conclude that the earth will continue to warm relative to whatever baseline "natural" process is happening because of this. The only question is by how much.
Any reasonable person would conclude that it makes sense for us to investigate ways to mitigate these impacts in order to avoid extremely expensive worst-case outcomes (rapid melting of the Antarctic ice sheets, coastal inundation, etc).
An unreasonable person would dismiss all this as some leftist religion and draw the line at any mitigation process that costs more than $0.01.