The author uses a new "empirical technique invoking three-cycle quasi-periodicity (TCQP) in Ap index" of solar geomagnetic activity to predict sunspot activity several years in advance.
The author notes solar activity was particularly active during the latter 20th century, stating, "the Sun has emerged from a Grand Maximum, which includes solar cycle 19, the most active solar cycle in the last 400 years. Earth was cooler in Grand Minima. The trend line indicates we have entered a period of low solar activity."
Indeed, the added red horizontal lines on the author's Annual Mean Sunspot Numbers show 50-year mean solar activity was at the highest levels of the past 300 years during the latter half of the 20th century:
|Added red horizontal lines show 50-year mean sunspot numbers were highest during the solar Grand Maximum in the latter half of the 20th century. DM= Dalton Minimum of solar activity during the Little Ice Age.|
Related: The Sun explains 95% of climate change over the past 400 years.