Climate Change and Human Occupation of the Sahara

• Main Authors: Blom, R. C., Farr, T., Feymann, J., Paillou, Philippe, Ruzmaikin, A.
• Other Authors: Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire aquitain des sciences de l'univers (OASU), Laboratoire d'Astrophysique de Bordeaux Pessac (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2008
• Subjects: Remote sensing; Solar variability Insolation forcing; [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP]; [PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP]; Greenland
• Online Access: https://hal.science/hal-00405738

The Sahara was void of settlement throughout the Last Glacial Maximum (LGM) and terminal Pleistocene (Kuper and Kreopelin, 2006). During early Holocene abrupt arrival of monsoon rains ~10,500 yrs BP produced a savanna allowing Human occupation. Between ~9.5 and ~7 kyrs BP was the wettest phase of the last 25,000 years across much of the Levant and Eastern Mediterranean (Robinson et. al., 2006). Kuper and Kreopelin, (2006) show timing of human occupation via archaeological data from Egypt, Sudan, Libya and Chad, with maximum human habitation in the Sahara North of 25 degrees at ~ 7.7 kyrs BP. Details of temporal variations in the Sun, and influence of these variations on the Earth's climate, remain contentious. None-the-less, analyses of paleoclimatic data and modeling (c.f. Braconnot et. al., 2007a, 2007b, 2008) indicate notable effects on human activities. We explore relationship of human occupation of the Sahara and long-term solar irradiance variations synergetic with atmospheric-ocean circulation patterns. The non-linear nature of climate change diminishes value of linear regression methods often used. To address these issues of non-stationary and non-linearity we applied wavelet decomposition and a new method, Empirical Mode Decomposition (EMD, Huang et al., 1998), designed account for non-linear/non-stationary features of the signals. EMD represents the data as a sum of a small number of orthogonal empirical modes that have time- variable amplitudes and frequencies. A mode has a symmetric envelope defined by the local maxima and minima so mean amplitude is zero everywhere. Mean period is determined by counting the number of peaks (maxima). Each mode is equivalent to an adaptively filtered signal in empirically determined (not imposed) frequency range. The last mode characterizes a nonlinear trend in the signal. The orthogonality of EMD modes prevents power leakage into a selected mode from other modes, an improvement over other types of filtering. We employ records taken over the globe (e.g. Greenland, ...