Toward a better understanding of the natural climatic variability Nicola Scafetta & Adriano Mazzarella Department of Earth, Environmental and Resources Science At the Porto Conference 2018: Porto (Po) - 7-8 September, 2018.

Summary We study the yearly values of the length of day (LOD, 1623-2016) and its link to the zonal index (ZI, 1873-2003), the Northern Atlantic oscillation index (NAO, 1659-2000) and the global sea surface temperature (SST, 1850-2016). LOD is herein assumed to be mostly the result of the overall circulations occurring within the ocean atmospheric system. We find that LOD is negatively correlated with the global SST and with both the integral function of ZI and NAO, which are labeled as IZI and INAO. The very high correlation between LOD and INAO since 1659 is interpreted as an implicit evidence that both the LOD and INAO records herein used are sufficiently accurate since the 17th century. Because of their high correlation with SST, we adopt the LOD and INAO records as global proxies to reconstruct past climate change. Tentative global SST reconstructions since the 17th century suggest that around 1700, that is during the coolest period of the Little Ice Age (LIA), SST was about 1.3 oC cooler than the 1950-1980 period. The estimated LIA cooling is greater than what some multiproxy global climate reconstructions suggest, but it well agrees with other climate reconstructions including those based on borehole temperature data.

(A) length of day - LOD (ms); (B) Zonal index (between 35°N and 55°N) - ZI (hPa); (C) Reconstruction of the North Atlantic Oscillation - NAO (hPa); (D) Sea surface temperature - SST (°C).

If the westerly flow is strong, the zonal index (ZI) is high If the westerly flow is strong, the zonal index (ZI) is high. In contrast, as the amplitude of the Rossby waves increases, the flow becomes less zonal and more meridional (i.e. it follows a north-south or longitudinal path). The ZI is then said to be low. For low ZI the net result is a significant latitudinal energy transfer which brings an increase of global surface temperature.

First case Integrated ZI : IZI(t)= IZI(t-1) +ZI(t) Integrated NAO: INAO(t) =INAO(t-1) +NAO(t) Geostrophic (zonal) winds (i.e. winds produced by equilibrium between the Coriolis force and meridional pressure gradient force that is set up by the temperature difference between the tropics and the Earth’s poles) are governed by the formula (Holton, 2004): where Ug is geostrophic (zonal) wind speed, g is the gravitational constant = 9.8 m/s2, Ω = (2π /LD) is the angular velocity of the Earth in radians, LD is the observed full length of day in seconds, φ is the angle of latitude, y is distance in the South-North direction and Δh is the height change of an atmospheric surface at a constant pressure over a fixed increment latitude Δy. Note that Δh is always positive since the height of a constant pressure surface in the atmosphere always decreases as you move from the tropics towards the pole. We observe that a variation of Ug , that is a DUg, is represented by a time integration of ZI or of NAO because these variables are the difference in surface pressure between two latitudes which determines the force generating the wind. Thus, a time integration of this pressure difference approximately determines the variation of the relative atmospheric momentum, that is, of the wind speed variation. The following approximate relation would hold if DUg is externally driven by, for example, solar/astronomical forcings: First case

Conservation of Angular Momentum If the involved processes were just internal a stronger westerly flow would require, if everything else remains constant, an slow down of the Earth's rotation. Secondcase

First case Time plot of standardized yearly values of LOD and IZI: (A) Raw values; (B) Smoothed according to a 5-yr running mean; (C) Smoothed according to a 11-yr running mean; (D) Smoothed according to a 23-yr running mean. First case

Time plot of standardized yearly values of LOD and SST: (A) Raw values; (B) Smoothed according to a 5-yr running mean; (C) Smoothed according to a 11-yr running mean; (D) Smoothed according to a 23-yr running mean. First case

First case Time plot of standardized yearly values of LOD and INAO: (A) Raw values; (B) Smoothed according to a 5-yr running mean; (C) Smoothed according to a 11-yr running mean; (D) Smoothed according to a 23-yr running mean. First case

(A) SST modelled using LOD (B) SST modelled using INAO

Borehole Global surface Temperature Estimates Huang, S. P., Pollack, H. N., Shen, P.-Y., 2008. A late Quaternary climate reconstruction based on borehole heat flux data, borehole temperature data, and the instrumental record. Geophys. Res. Lett., 35, L13703.

Global Surface Temperature

The IPCC climate models overestimate the CO2 effect and understimate the solar effect corrected models

Sun - Climate Coupling

Holocene temperature vs. solar records Comparison of solar activity (total solar irradiance [TSI]) in blue and δ18O from Dongge cave, China, in green representing changes of the Asian climate. Possibly the Asian monsoon (AM) (low δ18O corresponds to strong AM monsoon and vice versa). Comparison of solar activity (total solar irradiance [TSI]) in blue and δ18O from Dongge cave, China, in green representing changes of the Asian climate. possibly the Asian monsoon (AM) (low δ18O corresponds to strong AM monsoon and vice versa). TSI has been reconstructed from the cosmic ray intensity reconstruction (SI Appendix, Section S10). Both records have been normalized (subtraction of mean value and division by the standard deviation), linearly detrended and high-pass filtered with 2,000 y. (A) Time series of solar activity (TSI) and δ18O. Solar activity (TSI) is plotted on a reversed scale. (B) Wavelet of solar activity (TSI). De Vries cycle at approximately 210 y and Eddy cycle at approximately 1,000 y are marked with horizontal, gray dashed lines. Black boundaries mark 95% significance level. (C) Wavelet coherence of solar activity (TSI) and δ18O. De Vries cycle at approximately 210 y and Eddy cycle at approximately 1,000 y are marked with horizontal, gray dashed lines. Arrows pointing to the right indicate that the records are in phase. Black boundaries mark the 95% significance level. Steinhilber F et al. PNAS 2012;109:5967-5971 ©2012 by National Academy of Sciences

Climate sensitivity to CO2 doubling mean IPCC GCM = 3 oC recent estimates < 2 oC

Scafetta's 2008-2013 Forecast

Scafetta's 2013 Model

Eccentricity variation of Jupiter and Saturn

60 and 1000 year cycles

A pulsing Heliosphere

Conclusion 1) LOD can change because of: a) internal forcing as a response to the conservation of the Earth’s angular momentum; b) an external solar/astronomical induced torques alter the atmosphere and oceanic circulation which then induces a LOD change facilitated by the surface friction between the westerly zonal winds and the underlying solid Earth. The found negative correlation between LOD and INAO, IZI and SST implies that the most relevant mechanism is (b): the external torque mechanism. 2) Using INAO and LOD as proxies, the Little Ice Age was about bout 1.3 oC cooler than the 1950-1980 period. This is more than most global temperature reconstructions but it is compatible with borehole estimates. 3) Climate sensitivity to CO2 may be quite small !!!