Getting back on subject;
"New(2005) evidence suggests that concentrations of CO2 started rising about 8,000 years ago, even though natural trends indicate they should have been dropping."
The average CO2 ppm for over a million years varied from 180 to 280 ppm, averaging 230 ppm. At the start of the use of fossil fuel in large amounts it had risen to near the upper variable, 275 ppm. Since then it has risen to now over 395 ppm. The agricultural plant hardiness zone map from the USDA in a separate thread showed a +5*F change from 1993 to 2012 (add 1/2*F rise from 1980 to 1993).
Human inputs or causes may have lead to perhaps a 40 ppm or more increase in CO2 in thousands of years, but in the past 180 years or so it has gone up geometrically another 120 ppm from human fossil fuel burning, and increasing slash and burn agriculture.
This lead to a stimulated mammal population crash curve during this recent period, and not in the past pre-coal era. In the pre-coal era human causes were an average increase per year of only ~.005 ppm, then once coal (then other fossil fuel) was burned profusely it accelerated to the present ~+3 ppm per year.
