HR: 16:20h
AN: GP54A-01 INVITED     [Abstracts]
TI: Does the earth's magnetic field influence climate?
AU: * Courtillot, V
EM: courtil@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Place Jussieu, Paris, 75005, France
AU: Fluteau, F
EM: fluteau@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Place Jussieu, Paris, 75005, France
AU: Gallet, Y
EM: gallet@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Place Jussieu, Paris, 75005, France
AU: Le Mouel, J
EM: lemouel@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Place Jussieu, Paris, 75005, France
AB: The main agents which are invoked are solar variability, changes in atmospheric greenhouse gas content, or internal variability of the coupled ocean-atmosphere system. Evidences for connections between climate and magnetic field variations have received less attention and will be reviewed. On the 10-100yr timescale, that of recent secular variation, there appears to be a rather good correlation between decadal changes in amplitude of geomagnetic variations of external origin, solar irradiance and global temperature. The correlation applies until the 1980's, suggesting that solar irradiance may be a key forcing function of climate until then, when the correlation breaks and (anomalous?) warming may emerge from the signal (this is the subject of separate, ongoing work). Indeed, only solar flux of energy and particles can jointly explain such parallel variations in temperature and external magnetic field. On the 100-5000yr timescale, that of historical and archeomagnetic change, intriguing features are the recently proposed archeomagnetic jerks, i.e. fairly abrupt (~100 yr long) geomagnetic field variations found at irregular intervals over the past few millennia, using the archeological record from Europe to the Middle East. These seem to correlate with significant climatic events in the eastern North Atlantic region. A proposed mechanism involves variations in the geometry of the geomagnetic field (f.i. tilt of the dipole to lower latitudes), resulting in enhanced cosmic-ray induced nucleation of clouds. On the 103-106 yr timescale, that of excursions and reversals, evidence for correlations in field intensity changes, excursions and reversals, which invoke Milankovic forcing in the core, either directly or through changes in ice distribution and moments of inertia of the Earth, is proposed but is still rather tenuous. In conclusion, no forcing factor, be it changes in CO2 concentration in the atmosphere or changes in cosmic ray flux modulated by solar activity and geomagnetism, or possibly other factors, can at present be neglected or shown to be the overwhelming single driver of climate change in the past century. Intensive data acquisition is required to further probe indications that the Earth's and Sun's magnetic fields may have significant bearing on climate change at time scales going from years to millennia, and more.
DE: 1522 Paleomagnetic secular variation
DE: 1555 Time variations: diurnal to decadal
DE: 1560 Time variations: secular and longer
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly