Solar and planetary oscillation control on climate change: hind-cast, forecast and a comparison with the CMIP5 GCMs

TL;DR

This paper presents an empirical model based on astronomical harmonics that better reconstructs historical climate oscillations and suggests natural factors significantly influence recent warming, contrasting with traditional GCMs.

Contribution

It introduces an empirical climate model incorporating astronomical harmonics, outperforming GCMs in hind-casting and providing new insights into natural versus anthropogenic climate influences.

Findings

Natural oscillations account for 50-60% of observed warming since 1850.

Projected temperature increase from 2000 to 2100 is between 0.3°C and 1.6°C.

Climate sensitivity to CO2 doubling is centered at 1.35°C, ranging from 0.9°C to 2.0°C.

Abstract

Global surface temperature records (e.g. HadCRUT4) since 1850 are characterized by climatic oscillations synchronous with specific solar, planetary and lunar harmonics superimposed on a background warming modulation. The latter is related to a long millennial solar oscillation and to changes in the chemical composition of the atmosphere (e.g. aerosol and greenhouse gases). However, current general circulation climate models, e.g. the CMIP5 GCMs, to be used in the AR5 IPCC Report in 2013, fail to reconstruct the observed climatic oscillations. As an alternate, an empirical model is proposed that uses: (1) a specific set of decadal, multidecadal, secular and millennial astronomic harmonics to simulate the observed climatic oscillations; (2) a 0.45 attenuation of the GCM ensemble mean simulations to model the anthropogenic and volcano forcing effects. The proposed empirical model outperforms the GCMs by better hind-casting the observed 1850-2012 climatic patterns. It is found that: (1) about 50-60% of the warming observed since 1850 and since 1970 was induced by natural oscillations likely resulting from harmonic astronomical forcings that are not yet included in the GCMs; (2) a 2000-2040 approximately steady projected temperature; (3) a 2000-2100 projected warming ranging between 0.3 $^{o}C$ and 1.6 $^{o}C$, which is significantly lower than the IPCC GCM ensemble mean projected warming of 1.1 $^{o}C$ to 4.1 $^{o}C$; ; (4) an equilibrium climate sensitivity to $CO_{2}$ doubling centered in 1.35 $^{o}C$ and varying between 0.9 $^{o}C$ and 2.0 $^{o}C$.