Using the annual temperature anomaly data from GISS, in combination with annual CO2 data from NOAA, the temperature increase per atmospheric CO2 ppm increase can be calculated.
Now, if global warming is solely a function of increases in atmospheric CO2 levels, then calculating the degree increase per ppm added would be a convenient measure to monitor.
As this chart reveals, for the 50-year period ending 1963, for each ppm increase of CO2 there was an associated increase of +0.024°C; in contrast, for the 50-year period ending 2013, the impact on warming was 67% less per ppm.
This diminishing influence of a new CO2 molecule over time is actually a function of known climate physics - the logarithmic effect of carbon dioxide. Essentially, from lab testing it was determined that increasing levels of CO2 caused a diminishing returns effect, which is better described here.
The logarithmic relationship between CO2 levels and global temperature was first presented way back in the 1930s by a scientist named Guy Callendar, and it is now widely accepted as science fact.
And as the entire world knows by now, global warming is stuck in 'The Hiatus' that has resulted in temperatures barely budging over the last 16 years. This is despite the prodigious amounts of new CO2 emissions over that time span - recall, as the chart indicates, the influence of CO2 has declined.
What this means is that future CO2 emission impacts will likely continue to lessen, to the point where they become rather inconsequential, which the climate may already be approaching in a manner faster than expected.
Certainly, it would seem this fellow Callendar was really onto something. Plus, he discounted the speculative idea that higher levels of CO2 would create a positive feedback supposedly leading to ever higher temps. It appears he was wise to dismiss the shaky concept of "tipping point" positive feedbacks.
Not bad for a scientist without the "benefits" of super-computers, satellites, IPCC conferences, huge government funding of climate research and etc.
Additional temperature and climate charts.