In reply to tusenfem:
Look at figure 12 in the attached which shows the number of solar magnetic storms per year, from 1865 to present and the corresponding number of sunspots. There is a roughly 20 times increase in the number of magnetic storms at the end of the solar cycles, when comparing the 20th century to the 19th century.
http://www.geomag.bgs.ac.uk/earthmag.html#_Toc2075558
Background:
Mechanism:
The paleo record shows both a period of warming similar to the 20th century and cooling. The warming is hypothesized to be caused by electroscavenging were solar wind bursts create a space charge in the ionosphere which removes cloud forming ions. The second mechanism is solar modulation of Galactic Cosmic Rays (GCR). More GCR more clouds (cooler planet) and less GCR less clouds (warmer planet). This paper by Brian Tinsley and Fangqun Yu “Atmospheric Ionization and Clouds as Links Between Solar Activity and Climate” outlines the two mechanisms.
http://www.utdallas.edu/physics/pdf/Atmos_060302.pdf
Paleo Record
The paleoclimatic record indicates that in the past there have been a series of abrupt climatic changes, at which time there is concurrent solar magnetic field changes. The abrupt climatic changes were confirmed as they are found in multiple independent proxy sources. (Ocean floor sediment, ice core data, and so forth.) There is smoking gun evidence that changes in the sun are causing abrupt climate change on the earth.
The question is: What is the mechanism? TSI changes are not enough to cause the temperature changes observed. Kaplan’s recent paper 2006 indicates that the abrupt climate changes are global, affecting both hemispheres simultaneously, which rules out orbital changes of insolation as the driver, as orbital changes in insolation affect each hemisphere roughly 90 degrees out of phase.
This paper for example, discusses the Younger Dryas abrupt temperature change. The largest solar change in the last 20 kyrs is noted to occur at the same time the planet abrupt changes from interglacial back to glacial.
Reduced solar activity as a trigger for the start of the Younger Dryas? By Hans Renssen et al.
http://www.geo.vu.nl/~renh/pdf/Renssen-etal-QI-2000.pdf
From the Younger Dryas paper:
Quote:
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Estimates for the increase in 14C at the start of the YD all demonstrate a strong and rapid rise: 40-70 %/% within 300 years (Goslar et al., 1995), 30-60%/% in 70 years … (Hughen et al.,1998) and … in 200 years (Hajdas et al., 1998). This change is apparently the largest increase of atmospheric 14C known from late glacial and Holocene records (Goslar et al., 1995). Hajdas et al. (1998) used this sharp increase of atmospheric 14C at the onset of the YD as a tool for time correlation between sites. What are the possible causes for this large increase in atmospheric 14C? Geomagnetic variations are not a likely cause, since these generally act on a much longer timescale (i.e. millennia).
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