Interesting paper from Xhao & Feng finds strong coherence of De Vries 208 year millennial solar variation with temperature in Antarctica. Also finds incoherence between CO2 and temperature.
(a) Squared wavelet coherence between the SSN and T time series. The thick black contours indicate the 95% confidence level against red noise. Black arrows represent phase angles of the cross wavelet (with in-phase pointing right, anti-phase pointing left, SSN leading T by 90° pointing straight down, and SSN lagging T by 90° pointing straight up). The regions inside COI are removed. (b) The global wavelet coherence (Cg, solid line) and the phase angle strength (Sθ, dashed line) between SSN and T plotted against period. (c) Same as (a) but for the CO2 and T time series. (d) Same as (b) but for the CO2 and Ttime series. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
The solar impact on the Earth’s climate change is a long topic with intense debates. Based on the reconstructed data of solar sunspot number (SSN), the local temperature in Vostok (T), and the atmospheric CO2 concentration data of Dome Concordia, we investigate the periodicities of solar activity, the atmospheric CO2 and local temperature in the inland Antarctica as well as their correlations during the past 11,000 years before AD 1895. We find that the variations of SSN and T have some common periodicities, such as the 208 year (yr), 521 yr, and ~1000 yr cycles. The correlations between SSN and T are strong for some intermittent periodicities. However, the wavelet analysis demonstrates that the relative phase relations between them usually do not hold stable except for the millennium-cycle component. The millennial variation of SSN leads that ofT by 30–40 years, and the anti-phase relation between them keeps stable nearly over the whole 11,000 years of the past. As a contrast, the correlations between CO2 and T are neither strong nor stable. These results indicate that solar activity might have potential influences on the long-term change of Vostok’s local climate during the past 11,000 years
Global warming is one of the hottest as well as the most debatable issues in both the scientific and public community at present. Many factors are thought to be the potential reasons to cause the present warming, such as atmospheric circulation, surface conditions of the Earth, human activities, solar activities and volcanic activities. Solar activities, often denoted by the sunspot number (SSN), refer to transient processes occurring in solar atmosphere and lower layers. They have been believed to be the natural force to drive the long-term change of the Earth’s climate for a long time. As early as 1801, Herschel suggested that solar activity may play a role in the variability of the Earth’s climate, and found that the rainfall was reduced on the Earth when SSN was few on the Sun (Herschel, 1801). Many subsequent papers provided more and more evidences on good correlations between solar activities and some climate indexes. For example, the “Maunder Minimum” of solar activity (AD 1645–AD 1715) coincided well with the coldest excursion of the “Little Ice Age” (Eddy, 1976). Climate elements (air temperature, sea-level, and so on) were found to have some solar-cycle signals (e.g.,Currie, 1979). Strong correlations were uncovered between solar activities and the northern hemisphere temperature, revealing a direct solar influence on the Earth’s climate (Christensen and Lassen, 1991; Lean et al., 1995).
Some studies argued that the green-house gases released into the atmosphere since the industrial revolution are the main reason for the global warming in the 20th century (e.g.,Hegerl et al., 2007). However, the Earth’s temperature shows a big variability before the period of anthropogenic influence, such as the Medieval Warm Period (AD 900–AD 1300) and the Little Ice Age (AD 1550–AD 1850). This demonstrates that natural forces without modern human activities can also lead to strong climate variability, and their effects should not be neglected in the present climate change.