Discussion on climate oscillations: CMIP5 general circulation models versus a semi-empirical harmonic model based on astronomical cycles

Abstract

Power spectra of global surface temperature (GST) records (available since 1850) reveal major periodicities at about 9.1, 10-11, 19-22 and 59-62 years. Equivalent oscillations are found in numerous multisecular paleoclimatic records. The Coupled Model Intercomparison Project 5 (CMIP5) general circulation models (GCMs), to be used in the IPCC Fifth Assessment Report (AR5, 2013), are analyzed and found not able to reconstruct this variability. In particular, from 2000 to 2013.5 a GST plateau is observed while the GCMs predicted a warming rate of about 2 o C/century. In contrast, the hypothesis that the climate is regulated by specific natural oscillations more accurately fits the GST records at multiple time scales. For example, a quasi 60-year natural oscillation simultaneously explains the 1850-1880, 1910-1940 and 1970-2000 warming periods, the 1880-1910 and 1940-1970 cooling periods and the post 2000 GST plateau. This hypothesis implies that about 50% of the ∼ 0.5 o C global surface warming observed from 1970 to 2000 was due to natural oscillations of the climate system, not to anthropogenic forcing as modeled by the CMIP3 and CMIP5 GCMs. Consequently, the climate sensitivity to CO 2 doubling should be reduced by half, for example from the 2.0-4.5 o C range (as claimed by the IPCC, 2007) to 1.0-2.3 o C with a likely median of ∼ 1.5 o C instead of ∼ 3.0 o C. Also modern paleoclimatic temperature reconstructions showing a larger preindustrial variability than the hockey-stick shaped temperature reconstructions developed in early 2000 imply a weaker anthropogenic effect and a stronger solar contribution to climatic changes. The observed natural oscillations could be driven by astronomical forcings. The ∼ 9.1 year oscillation appears to be a combination of long soli-lunar tidal oscillations, while quasi 10-11, 20 and 60 year oscillations are typically found among major solar and heliospheric oscillations driven mostly by Jupiter and Saturn movements. Solar models based on heliospheric oscillations also predict quasi secular (e.g. ∼ 115 years) and millennial (e.g. ∼ 983 years) solar oscillations, which hindcast observed climate oscillations during the Holocene. Herein I propose a semi-empirical climate model made of six specific astronomical oscillations as constructors of the natural climate variability spanning from the decadal to the millennial scales plus a 50% attenuated radiative warming component deduced from the GCM mean simulation as a measure of the anthropogenic plus volcano contribution to climatic changes. The semi-empirical model reconstructs the 1850-2013 GST patterns significantly better than any CMIP5 GCM simulation. Under the same CMIP5 anthropogenic emission scenarios, the model projects a possible 2000-2100 average warming ranging from about 0.3 o C to 1.8 o C. This range is significantly below the original CMIP5 GCM ensemble mean projections spanning from about 1 o C to 4 o C. Future research should investigate spaceclimate coupling mechanisms in order to develop more advanced analytic...

ACRIM total solar irradiance satellite composite validation versus TSI proxy models

“…The Coupled Model Intercomparison Project Phase 5 (CMIP5) used to study climate change (Scafetta 2013c) currently recommends the use of a solar forcing function deduced from the TSI proxy model originally proposed by Lean and collaborators (Wang et al 2005;Kopp et al 2007). Lean's recent models show a relatively small secular trend (about 1 W/m 2 ) from the Maunder minimum (1645-1715) to the present with a peak about 1960 and it is quasi stationary since.…”

Natural climate variability, part 2: Interpretation of the post 2000 temperature standstill

“…This natural climatic variability is confirmed by historical inferences [11] and by climate proxy reconstructions spanning the entire Holocene [12,13]. A millennial climatic oscillation would suggest that a significant percentage of the warming observed since 1850 could simply be a recovery from the Little Ice Age of the 14 th -18 th centuries and that throughout the 20 th century the climate naturally returned to a warm phase as it happened during the Roman and the Medieval warm periods [9,11,[14][15][16].…”

“…Detailed data analysis [15,19] has concluded that the climatic effects of the radiative forcing is about half of that simulated by the CMIP5 GCMs. The climate sensitivity to CO2 doubling of the CMIP5 GCMs is about 3.…”

“…Since 2010 Scafetta [14,15,16,19,22] has proposed that the dynamics of the climate records suggests that the system is oscillating with specific harmonics that can be found in the gravitational and electromagnetic oscillation of the sun and of S22 the solar system. At the decadal to the millennial scales these oscillations have periods of: 9.1 year, which is a likely solarlunar tidal cycle; 10-11 year, which is the 11-year solar cycle that has been on average about 10.5 year during the 20 th century; quasi 20-year and 60-year oscillations, which are related to the major solar system oscillations due to the movement of Jupiter and Saturn; quasi 115-year and 980-year, which are related to specific major beats between planetary and solar oscillations.…”

“…Finally, for the post 2000 period we compare the predictions of the CMIP5 GCMs used by the IPCC [2013], against that of two semi-empirical models proposed a few years ago [15,19]. These models were based on a specific number of natural oscillations suggested by astronomical considerations plus an anthropogenic warming effect strongly reduced by 50% relative to the GCM predictions.…”