Modeling and Forecasting Climate Change: CMIP5 General Circulation Models versus a Semi-Empirical Model Based on Natural Oscillations

Since 1850 the global surface temperature (GST) has warmed by about 0.9 oC. The CMIP5 general circulation climate models (GCMs) adopted by the IPCC in 2013 have projected that the GST could rise by 2-5 oC from 2000 to 2100 for anthropogenic reasons. These projections are currently used to justify expensive mitigation policies to reduce the emission of anthropogenic greenhouse gases such as CO2. However, recent scientific research has demonstrated that those GCMs do not properly reconstruct the natural variability of the climate. The latter is mostly made of oscillations spanning from the decadal to the millennial scales (e.g. with periods of about 9.1, 10.4, 20, 60, 115, 1000, 2100-2500 years and others). I show that these oscillations are synchronized to the major solar and astronomical oscillations of the solar system driven by the revolution of the Jovian planets around the Sun and to specific long-scale solar-lunar tidal oscillations on Earth. A semi-empirical model of climate change based on these oscillations is demonstrated to outperform the CMIP5 GCMs in reconstructing the historical global surface temperature record. The same model, which has been first proposed in 2011, has well agreed with the GST data up to the present day. The model also uses the same volcano and anthropogenic forcing functions adopted by the CMIP5 GCMs, but it predicts a climate sensitivity to CO2 doubling that is half than the CMIP5 GCMs’ one (a mean value of about 1.5 °C versus 3.0 °C), which is consistent with a number of recent studies. The semi-empirical model projects a very moderate warming until 2040 and a warming less than 2 oC from 2000 to 2100 using the same IPCC anthropogenic emission scenarios. Thus, climatic adaptation policies should be sufficient to address the negative consequences of a global warming during the 21st century.