Method uses the Ap geomagnetic index, which has been in a slump since October 2005:
The Hockey Schtick tips us to a paper published today in Advances in Space Research predicts that if the current lull in solar activity “endures in the 21st century the Sun shall enter a Dalton-like grand minimum. It was a period of global cooling.”
The graph they produced with the paper:
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 has been at a higher level in the 20th century saying”
“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.”
Note the red horizontal line on the graph show 50-year mean solar activity was at the highest levels of the past 300 years during the latter half of the 20th century.
The author also has a slide show that has some interesting elements. For example, here is their TCQP of the Ap Index:
An empirical approach to predicting the key parameters for a sunspot number cycle
H.S. Ahluwalia University of New Mexico, Department of Physics & Astronomy
The common methodologies used to predict the smooth sunspot number (SSN) at peak (Rmax) and the rise time (Tr) for a cycle are noted. The estimates based on geomagnetic precursors give the best prediction of Rmax for five SSN cycles (20-24). In particular, an empirical technique invoking three-cycle quasi-periodicity (TCQP) in Ap index has made accurate predictions of Rmax and Tr for two consecutive SSN cycles (23 and 24). The dynamo theories are unable to account for TCQP. If it endures in the 21st century the Sun shall enter a Dalton-like grand minimum. It was a period of global cooling. The current status of the ascending phase of cycle 24 is described and the delayed reversal of the solar polar field reversal in the southern hemisphere in September 2013 is noted.
Open access here: http://www.sciencedirect.com/science/article/pii/S0273117713007473
Annual Mean Sunspot Numbers