The debate over global warming theory is turning into a contest between two explanatory models for climate change: human activity or solar activity. Now comes news that solar activity may be declining, signaling that we may (no alarmism here) be entering a period of global cooling. Investor's Business Daily explains:

Kenneth Tapping, a solar researcher and project director for Canada's National Research Council, is among those looking at the sun for evidence of an increase in sunspot activity.

Solar activity fluctuates in an 11-year cycle. But so far in this cycle, the sun has been disturbingly quiet. The lack of increased activity could signal the beginning of what is known as a Maunder Minimum, an event which occurs every couple of centuries and can last as long as a century.

Such an event occurred in the 17th century. The observation of sunspots showed extraordinarily low levels of magnetism on the sun, with little or no 11-year cycle.

This solar hibernation corresponded with a period of bitter cold that began around 1650 and lasted, with intermittent spikes of warming, until 1715. Frigid winters and cold summers during that period led to massive crop failures, famine and death in Northern Europe.

As we have noted many times, perhaps the biggest impact on the Earth's climate over time has been the sun.

For instance, researchers at the Max Planck Institute for Solar Research in Germany report the sun has been burning more brightly over the last 60 years, accounting for the 1 degree Celsius increase in Earth's temperature over the last 100 years.

R. Timothy Patterson, professor of geology and director of the Ottawa-Carleton Geoscience Center of Canada's Carleton University, says that "CO2 variations show little correlation with our planet's climate on long, medium and even short time scales."

Rather, he says, "I and the first-class scientists I work with are consistently finding excellent correlations between the regular fluctuations of the sun and earthly climate. This is not surprising. The sun and the stars are the ultimate source of energy on this planet."

Patterson, sharing Tapping's concern, says: "Solar scientists predict that, by 2020, the sun will be starting into its weakest Schwabe cycle of the past two centuries, likely leading to unusually cool conditions on Earth."

"Solar activity has overpowered any effect that CO2 has had before, and it most likely will again," Patterson says. "If we were to have even a medium-sized solar minimum, we could be looking at a lot more bad effects than 'global warming' would have had."