While CO2 has increased by 85 ppm from when measurements began in 1958 and are estimated to have risen by 120 ppm since 1750, we should also realize that increases of 80 ppm to 100 pm occurred during the last 3 glaciations without humans burning fossil fuels.
” Air trapped in bubbles in polar ice cores constitutes an archive for the reconstruction of the global carbon cycle and the relation between greenhouse gases and climate in the past. High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased by 80 to 100 parts per million by volume 600 ± 400 years after the warming of the last three deglaciations. Despite strongly decreasing temperatures, high carbon dioxide concentrations can be sustained for thousands of years during glaciations; the size of this phase lag is probably connected to the duration of the preceding warm period, which controls the change in land ice coverage and the buildup of the terrestrial biosphere.”
http://www.sciencemag.org/content/283/5408/1712.abstract
sunshine hours 