we were in a cooling phase of an approaching ice age event and the massive release of CO2 due to humans consuming stored carbon is what caused the departure from the trend. The climate response to changes in CO2 is well documented in the stratigraphy of very old glaciers, such as on Antarctica. Small bubbles in the ice from known ages (stratigraphy again) have the amount of CO2 trapped in them in measurable amounts and there is direct correlation between CO2 concentrations and global temperature. You should ask your geology instructors for a refund, since it apparently didn't take.