There is still a battle between the extreme pessimist and different degrees of optimist/realists over the impact of Greenhouse Gases, primarily CO2 - Carbon Dioxide "Climate". Since atmospheric CO2 is one of the factors that we have reasonable good data on, it makes a reasonable good proxy or reference to relate changes in our atmosphere to changes in our "climate". There are many other factors that can impact "climate", but most have much less recorded data. There is another issue with what is "climate"?
Here is a simple illustration of CO2 being used as a reference. Since the current data should be the most reliable, the baseline for this graph is the Mauna Loa CO2 sampling period from 1959 to 2013 or all the full years, J-D, converted to a temperature anomaly form using the simple ln(CO2/CO2ref) times scaling factors of 1.6 and 3.0. Since the natural log (ln) of a doubling of CO2 concentration would be about 0.69, the "sensitivity" would be about 1.1 C for the 1.6 scale which is about the no feedback value for CO2 all by itself and 2.1 C for the 3.0 scaling factor which is the lower end of the IPCC estimates for CO2 only. I could have divided by the ln(2) for a direct relationship to temperature per doubling, but this way people will actually have to read in order to see what the curves mean. Along with the two CO2 reference curves is the normally ice free ocean area surface temperature from 60S to 60N from the ERSSTv3b SST data set available at KNMI Climate Explorer. From 1958 to Mauna Loa CO2 data is used and prior to that the Berkeley interpolated data is used. The ERSSTv3b is shown both as monthly anomaly and in a 60 year moving average assuming 60 year averages can be considered Climate. This assumption should reduce the tenancy to cherry pick shorter periods that might not be long enough to be called "Climate".
The 1.6lnCO2 appears to match the ocean SST very well for the 60 YMA and the 3.0lnCO2 better match the 1970 to present portion of the SST curve. Now remember that the CO2 references would also include all the "other" factors, anthropogenic and natural. The object of this post is to see how pessimists, optimists and realists might interpret this simple comparison.