Carbon dioxide in the atmosphere is expected to increase heat energy retained in the atmosphere by 1 to 1.5 degrees C for each doubling of concentration, "all else remaining equal". All else remaining equal is a rather large assumption.
To make it easier to see, here is just the Northern Hemisphere starting in 1900 using a 5 year centered moving average with a 1961 to 1990 baseline. The 5 year averaging is just to reduce some on the noise without lossing too much of the signal and the 1961 to 1990 baseline is to make it easier to compare the instrumental data to the numerous plaeo climate reconstructions of past temperatures. Note that the light blue curve is Tmin. The slope of this curve is more consistently rising from the 1900 start than the Tmax and sea surface temperature(SST). The end value of Tmin is approximately 1.8 degrees C warmer than it was at the start. The greatest rise in the Tmin slope starts about 1970 and is approximately 1.3 degrees. The start of that slope followed an approximately 0.3 degree drop beginning around 1960.
Comparing the hemispheres, it doesn't look promising that "all things remained equal". The CO2 increase should have its largest measurable impact on the average minimum surface temperature and should be greater over land than the oceans. With the southern hemisphere having much more oceans influence than the northern hemisphere, the doubling of the slope in the SH versus the tripling of the slope in the NH is not unexpected. The slope of both hemispheres prior to the 1965 change, would not as likely be due to CO2 increases. As a rough estimate, half of the SH warming would be unrelated to CO2 forcing and possible one third of the NH warming would also be unrelated to CO2. The curve in the SH series from 1965 to 2010 has the appearance of a dampened response, not in keeping with CO2 forcing, which implies more natural variability than generally mentioned by Anthropogenic Global Warming affectionadoes.
While swaying the "believers" in AGW is unlikely, rational skepticism of AGW being primarily due to CO2 forcing appears logical deduction not denial of proven science. The "believers" perhaps should spend some time analyzing their own motivations.
Added Tmax and SST for the curious: