A new model explaining variation in the sun’s output suggests Earth is due for a “mini ice age” in the 2030s.

Astronomers have long observed that the number of sunspots varies over a cycle lasting approximately 11 years. At the peak of that cycle, there are more sunspots visible; at the low point, there are fewer.

Sunspots are an indication of more energy being released, which hurtles toward earth, leading to slightly higher temperatures on the ground, all else being equal.

Scientists have also long been puzzled about why each cycle has different high and low points.

For example, one particularly deep low point occurred in 1680, corresponding with a mini ice age that brought average temperatures in North America and Eurasia down by more than half a degree.

It was a period when glaciers extended over what’s now farmland, sea ice was more extensive, and canals of the Netherlands regularly froze, according to NASA.

That really deep low point was named the “Maunder minimum,” after the nineteenth-century astronomer E. Walter Maunder, who attempted to explain why the cycles vary.

This new model not only explains the variation, but suggests the next Maunder minimum is coming between 2030 and 2040.

The model was proposed last week at a meeting of the United Kingdom’s Royal Astronomical Society by Prof. Valentina Zharkova, of Northumbria University.

Zharkova and colleagues believe the variation between cycles can be explained by the existence of two dynamos -- phenomena that govern the sun’s magnetic fields.

They believe one of the dynamos is deep in the sun and the other is closer to the surface, with both moving around in cycles of approximately 11 years.

According to the new model, between 2030 and 2040, “the two waves will exactly mirror each other – peaking at the same time, but in opposite hemispheres of the Sun,” Zharkova said.

When that happens, their magnetic effects “will nearly cancel each other.” In other words, that cycle’s low will have the deepest low point, just like the one that occurred in 1680.

Patrick Hall, an astronomy professor at York University, cautions that the model is very new. But he said that if it allows scientists to more accurately predict the sunspots, “that would be a big advance.”

As for the “mini ice age,” Hall cautions the effects would only be temporary and climate change from man-made greenhouse gases would have a greater impact on Earth temperatures in coming decades.

“Even if their theory turns out to be correct and there is a reduction in the amount of light and heat from the sun,” he said, “the greenhouse gases will still be there.”