Global warming projections to 2100 using simple CO2 greenhouse gas modeling and comments on CO2 climate sensitivity factor

As global climate change auspiciously transcends national boundaries, it is imperative to make effective treaties to reduce greenhouse gas (GHG) emissions (e.g., CO2 in particular) while improving energy usage efficiency. The scientific community through the Intergovernmental Panel on Climate Change (IPCC) has made reasonable anthropogenic global warming (AGW) predictions. However, the IPCC models have failed to predict the global warming pause since ca. 2000 to 2014. The 1880-2015 global temperature anomaly (GTA) can be modelled by the equation proposed in part by Loehle and Scafetta, 2011, Open Atmos. Sci. J. 5, 74-86 with the incorporation of the CO2 sensitivity factor (c) in this work: GTA=a∗cos(ω∗(y−1880)+ϕ)+c∗ln([CO2]y/[CO2]1958)+d∗(y−1958)+e where a (amplitude) = 0.15 °C, ω (angular frequency) = 2.π/58 rad y−1, ϕ (phase shift) = −0.05 rad, c (climate sensitivity factor) = 2.52 °C, y = year, d = 0.0013 °C y−1 (global warming since the Little Ice Age), [CO2] is the atmospheric CO2 concentration (in ppm), and e (constant) = −0.02 °C. The extracted model CSF (2.52 °C (CSF)) is in excellent agreement with an earlier value of 2.52 °C (Callendar, 1938, Quart. J. Roy. Meteorol. Soc. 64, 223-240 - corresponds to 283 K, a water vapor pressure of 1,000 Pa, and a [CO2] range of 100-600 ppm), but is significantly smaller than the average IPCC AR5 CSF (4.33 °C). Hence, a more reasonable CSF would be 2.52 °C based on actual GTA data in the present work modeling. From that equation, the 2100 GTA is projected to be −0.3, 0.7, and 1.8 °C under 3 representative 100.Δ[CO2]/([CO2].Δyear change scenarios of −0.5, 0.0, and 0.5%.y−1, respectively, compared to the 2015 GTA of 0.9 °C. The COP21 agreement calls for the GTA to be less than 1.4 °C (preferrably 0.9 °C) by 2100, and this can only be achieved if the increase in atmospheric CO2 level after 2015 is maintained at 0.0% per year.