I explain that as a graph showing the CO2 warming effect based on an unrealistic CO2 sensitivity.
Even the discredited Lindzen and Choi 2009 paper which calculated a global CO2 sensitivity based solely on tropical data attributes more warming to CO2 than the graph you have posted up:
Where did you get your graph from? Do you have a link?
Now, disregarding that your graph is bogus. The logarithmic behaviour of CO2 warming is well known. The first 20-40ppm of CO2 accounts for the majority of the warming. That is no secret. It is also well known that CO2 is a forcing and that it accounts for around 20% of the greenhouse gas warming that maintains the temperature 33°C higher than it would be if there were no greenhouse gasses in the atmosphere.
From that, the contribution to date from CO2 is approx 6.5°C. As we are not yet at thermal equilibrium with the current CO2 levels, and CO2 levels are still rising, the expected contribution to a doubling of CO2 post the industrial revolution will be in the order of 2-3°C. As CO2's contribution will be fraction of this value, with the rest being from feedbacks, the values presented in your graph using a reasonable CO2 sensitivity are entirely expected. Remembering that the values are cumulative.
