Discussion: In July 2018 the solar cycle sunspot number index (SCSNI) continued to emphasize presence of the latest solar minimum which began in late 2017/early 2018 (Fig. 1). The current SCSNI is lower than forecast by NASA. At onset, the 2018 solar minimum appears to be as strong as the 2007-2010 episode which was one of the strongest in the 400+ year historical data set (Fig. 2). Given the lengthy unusually strong solar minimum in 2007-2010 (solar minimum usually lasts 2 years) followed by the weakest solar maximum in nearly 100 years in 2012-2014 scientists have speculated a long duration relative inactive period of solar activity may be ahead.
The most recent relative inactive period of solar activity occurred roughly in the 1875-1925 time frame. The most famous period of inactive solar activity occurred in 1800-1830 given a name, the “Dalton Minimum”. There is general agreement that the earth’s atmosphere cooled by about 1C during the Dalton Minimum. Infamous was the Maunder Minimum occurring in 1645-1715 when sunspots were extremely rare. The Maunder Minimum occurred during the “Little Ice Age”
Whether we’re entering a long duration period of a relative inactive sun is speculative. Solar diagnostics suggest there is potential for that scenario. Relative inactive periods of solar cycle have uncertain influences on atmospheric temperature where stronger inactive periods cool the atmosphere sometimes to an extreme.
The earth’s atmosphere has been warming due to the influence of CO2 especially at high latitudes and causing the polar cap to shrink in the northern hemisphere. What would a weaker sun do to this trend?
Fig. 1: Solar cycle sunspot number progression in the current century identifying the character of the 11-year solar cycle.
Fig. 2: The 1750 to 2018 solar cycle sunspot number identifying the strength/character of the 11-year solar cycle.