If global warming is CO2-induced why is there so much more in the northern hemisphere?

Both satellite and surface-based temperature records show warming at almost twice the rate in the northern hemisphere as the southern:

Source: http://data.giss.nasa.gov/gistemp/graphs_v3/

RSS satellites show "global" warming trend more than double in Northern Hem. vs Southern Hem.

Now if you divide the globe into three latitudinal bands the north/south warming disparity is even greater:

Taking just the northern and the southern 1/3 latitudinal bands and superimposing them you can see this even greater disparity:

Carbon dioxide is a few more ppm in the northern hemisphere than the southern, however the rise these last few decades over all latitudes has been the same.

Given that CO2 warming is logarithmic and the starting ppm of CO2 is less in the southern hemisphere, there should if anything be a slight amount more of warming in the southern hemisphere, if in fact the warming was due to CO2.

If the warming of the late 20th century was due to CO2 wouldn't it be more even across all latitudes than shown above?