Probably the last in this series on cosmic rays and recent warming, we look at two recent papers on the position of the geomagnetic field and recent climate, most likely mediated by changes in cosmic ray flux.
Regional cosmic ray induced ionization and geomagnetic field changes by Kovaltsov and Usoskin examines regional effects on atmospheric ionization of the migration of the geomagnetic dipole axis over the last thousand years. The dipole migrated by 20 deg. of latitude and 180 deg. of longitude during the last 1000 years. This trajectory is compared with the cosmic ray flux (CRF) reconstructed from the cosmogenic isotope 14C from tree rings.
They present a picture of climate effects for two regions, Europe and the Far East. The variations for Europe show the familiar profile (inverted) of a Medieval Warm Period, a Little Ice Age and general warming over the last 200 years to the present. The picture for the Far East is for generally increasing warmth from about 1200 to the present.
The second paper points out a possible correlation of geomagnetic pole correlation and the last 100 years. Climate Change and the Earth’s Magnetic Poles, A Possible Connection: Energy & Environment, Volume 20, Numbers 1-2, January 2009 , by Kerton, Adrian K75-83(9).
Analysis of the movement of the Earthâ€™s magnetic poles over the last 105 years demonstrates strong correlations between the position of the north magnetic, and geomagnetic poles, and both northern hemisphere and global temperatures. Although these correlations are surprising, a statistical analysis shows there is a less than one percent chance they are random, but it is not clear how movements of the poles affect climate.
The analysis is speculative. The significance needs to be reduced as autocorrelation seems not to have been taken into account. However, this gives you a flavor of where this literature seems to be headed.
One unusual feature of these analyses are the correlations observed with longitude, explained by differential regional sensitivity to CRF flux. This is consistent with different areas of sensitivity actually observed in the paper by PallÃ©, where both Europe and the Far East emerged as areas with high correlation of atmospheric ionization, and low cloud.
The literature has identified a number of factors influencing CRF, with different origins and time scales, from the galactic, to solar, to the earth. So even though the CRF theory promotes a single mechanism for changing climate — effects on cloudiness — the multiple causes of variations presents a challenge, and risks of spurious correlations. While geomagnetic variations may seem minor to us, in fact even on millennial time scales, they could well be quite regionally significant:
We note that the migration of the magnetic pole during the
last millennium, which caused significant effects in cosmic ray induced ionization variations in some regions, was not exceptional. Actually, it can be regarded as a minor excursion (about 2000 km or 18 of a great circle during the millennium). There is evidence for more dramatic excursions of the geomagnetic axis, even for historical times. For example, the magnetic pole could have migrated for more that 90 of a great circle during the so-called â€œSterno-Etrussiaâ€ geomagnetic excursion around 700 BC (Dergachev et al., 2004). The corresponding changes in local CRII must then be dramatic and may result in strong regional effects.
Finally, the review of climate-geomagnetics in Are there connections between the Earth’s magnetic field and climate? by Courtillota, Galleta, Le MouÃ«la, Fluteaua and Genevey
Understanding climate change is an active topic of research. Much of the observed increase in global surface temperature over the past 150 years occurred prior to the 1940s and after the 1980s. The main causes invoked are solar variability, changes in atmospheric greenhouse gas content or sulfur due to natural or anthropogenic action, or internal variability of the coupled oceanâ€“atmosphere system. Magnetism has seldom been invoked, and evidence for connections between climate and magnetic field variations have received little attention. We review evidence for correlations which could suggest such (causal or non-causal) connections at various time scales (recent secular variation ~10â€“100 yr, historical and archeomagnetic change ~100â€“5000 yr, and excursions and reversals of ~103â€“106 yr), and attempt to suggest mechanisms. Evidence for correlations, which invoke Milankovic forcing in the core, either directly or through changes in ice distribution and moments of inertia of the Earth, is still tenuous. Correlation between decadal changes in amplitude of geomagnetic variations of external origin, solar irradiance and global temperature is stronger. It suggests that solar irradiance could have been a major forcing function of climate until the mid-1980s, when â€œanomalousâ€ warming becomes apparent. The most intriguing feature may be 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 (tilt of the dipole to lower latitudes), resulting in enhanced cosmic-ray induced nucleation of clouds. 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 past centuries. 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 certain time scales.