In reply to Ken G.
The information and analysis below seems to support the modulation of planetary cloud hypothesis by electroscavenging, hypothesis. If planetary clouds are reduced by an increase in solar wind bursts that through the process of electroscavenging, removes cloud forming ions, then a significant portion of the 20th century warming could have been caused by that mechanism.
The first paper states that the solar large scale magnetic field has more than doubled in the last 100 years. There are solar papers that link the formation of coronal holes which generate high speed solar winds, with the solar large scale magnetic field.
The second paper provides a model as to why the solar large scale magnetic field has more than doubled. I believe the e-folding time for a reduction in the large scale magnetic field is about 4 years.
The last link is to a geomagnetic research site that provides a 150 year record of the number of solar magnetic storms per year. (The solar magnetic storms cause short term alternation in the externally measure geomagnetic field. The geomagnetic field has been monitored for the last 150 years in England and Australia.) There are more than twice as many solar magnetic storms comparing the 20th century to the 19th century. As shown in figure 12, the number of solar magnetic storms is reduced in cycle 20, which is I believe when there was a period of global temperature reduction.
“Doubling Sun’s Coronal Magnetic Field in Last 100 years” by Lockwood et al.
http://www.nature.com/nature/journal.../399437a0.html
Quote:
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Here we show that measurements of the near-Earth interplanetary magnetic field reveal that the total magnetic flux leaving the Sun has risen by a factor of 1.4 since 1964: surrogate measurements of the interplanetary magnetic field indicate that the increase since 1901 has been by a factor of 2.3.
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Evolution of the Sun's large-scale magnetic field since the Maunder minimum by Solanki et al.
http://www.nature.com/nature/journal.../408445a0.html
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Here we present a model describing the long-term evolution of the Sun's large-scale magnetic field, which reproduces the doubling of the interplanetary field. The model indicates that there is a direct connection between the length of the sunspot cycle and the secular variations.
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Look at figure 12 in the attached which shows the number of solar magnetic storms per year, from 1865 to present and the solar cycle number. 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
Comment:
I started investigating this subject with a review of papers and textbooks, that outline what is known concerning abrupt climate change and the glacial/interglacial cycle. There are both warming and abrupt cooling periods in the paleoclimatic record. Some papers hypothesized that changes in ocean currents could be causing the abrupt climatic changes.
Kaplan’s finding (see comment above) that the planetary temperature changes (cooling and warming) are synchronous in both hemispheres appears to rule out ocean current changes (Changes in ocean currents warm one region and cool another.) Also the ocean current hypothesis requires an unstable system where a small forcing function would be amplified by positive feedback. There appears to be evidence for negative feedbacks which resist climatic change. With negative feedbacks the forcing function must be much larger to cause the observed large rapid temperature changes.