The relationship between CO2 and global warming

I came to the end of the discussion about Scott Sumner’s post discussing global warming. I posted a comment, but it was probably too late for most people to notice.

I think the issue is more complicated than Scott seems to suggest.

Scott writes:

Theory suggests that higher CO2 levels should increase global temperatures due to the “greenhouse effect.”

WHERE.

But what that doesn’t tell us is how strong the effect is. I don’t disagree with Scott. I’m just saying that the effect can be strong or weak. If a substantial increase in CO2 led to a temperature increase of 0.1 degrees C, we would have little to worry about. We cannot simply look at the fact that CO2 increased and then the temperature increased and attribute the entire temperature increase to the increase in CO2.

Take an example from the world of economics, which Scott and I are obviously more familiar with. We argue that a substantial increase in the minimum wage will lead to a substantial reduction in the number of jobs held by low-skilled workers. That’s just good economic theory. So when we look at the data, we see that an increase in the minimum wage of a few dollars per hour is certainly associated with a substantial reduction in the number of jobs held by low-skilled workers.

But that doesn’t tell us how much of the job decline is due to the minimum wage increase.

Likewise, focusing on one variable, CO2 concentration, and not looking at other factors that could be causing global warming is poor methodology.