The sun is also somewhat variable. Like almost everything in the natural world, it has cycles. One we know well is the 11-year sunspot cycle. That cycle varies the sun's output, and can impact temperatures here on Earth. But there's another, lesser-known cycle, the Gliissberg Cycle, that may have a bigger impact - and there are signs that it's about to kick into play again.

Watts Up With That's Anthony Watts has details.

You’ve heard of the 11-year sunspot cycle. But what about the Centennial Gleissberg Cycle? The Gleissberg Cycle is a slower 100-year modulation of sunspots. New research just published in the journal Space Weather suggests that the Gleissberg Cycle is waking up again, which could make solar cycles for the next 50 years increasingly intense. 

You’ve probably heard of the 11-year sunspot cycle. The Gleissberg Cycle is a slower modulation, which suppresses sunspot numbers every 80 to 100 years. For the past ~15 years, the sun has been near a low point in this cycle, but this is about to change.

New research published in the journal Space Weather suggests that the Gleissberg Cycle is waking up again. If this is true, solar cycles for the next 50 years could become increasingly intense.

So what does that mean? Intense solar cycles have the possibility of affecting things like satellites, which will take the brunt of increased solar output, and it looks like we're in for a more intense time:

The resurgence of the Gleissberg Cycle makes a clear prediction for the future: Solar Cycles 26 through 28 should be progressively intense. Solar Cycle 26, peaking in ~2036, would be stronger than current Solar Cycle 25, and so on. The projected maximum of the Gleissberg Cycle is around 2055, aligning more or less with Solar Cycle 28. That cycle could be quite intense.

There is a strong correlation between Gleissberg minima and cooler temperatures on Earth. Now, this is some turgid scientific writing here:

The recent extended, deep minimum of solar variability and the extended minima in the 19th and 20th centuries (1810–1830 and 1900–1920) are consistent with minima of the Centennial Gleissberg Cycle (CGC), a 90–100 year variation of the amplitude of the 11-year sunspot cycle observed on the Sun and at the Earth. The Earth’s climate response to these prolonged low solar radiation inputs involves heat transfer to the deep ocean causing a time lag longer than a decade. The spatial pattern of the climate response, which allows distinguishing the CGC forcing from other climate forcings, is dominated by the Pacific North American pattern (PNA). The CGC minima, sometimes coincidently in combination with volcanic forcing, are associated with severe weather extremes. Thus the 19th century CGC minimum, coexisted with volcanic eruptions, led to especially cold conditions in United States, Canada and Western Europe.

The thumbnail? The Centennial Cleissberg Cycle (CGC), during its 19th-century minima, was associated with colder temperatures. And now the Gliessberg cycle looks to be kicking into high gear.

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In this, as in any field of endeavor, predictions are hard to make, especially about the future. Evidence from past cycles, when there weren't any sophisticated weather-monitoring stations set up, and no devices to measure solar output, we are required to look at physical evidence (tree rings, isotope ratios, and so forth) and compare those apples to our modern-day oranges. That's less than ideal and gives us indications rather than hard data. But now it seems we're about to get a direct look at how the CGC will affect our modern climate, human influence, and all. 

My guess is that it will overshadow human efforts by a wide margin.

There are other cycles, as well, that affect the climate. The Milankovitch Cycles are in large part responsible for the fact that, for the last few hundred millennia, mile-thick ice sheets have been going up and down like window blinds, at least when measured on the geological time scale. These cycles also affect our climate, and as they are caused by the axial tilt of our planet in its orbit, along with the eccentricity of the elliptical orbit. These cycles are also something that is far beyond human influence, and these cycles are measured in thousands, not hundreds, of years.

The sun is 93 million miles away. But its output has far more impact on our planet's climate than suburban moms driving SUVs. As I've said and written for many years, human activities do, yes, have some effect. But the sun has far more, and now, with the CGC looking to be moving out of the recent minima, will be ramping up solar output. That will have some impact on Earth's climate; how much remains to be measured. But it's a fair bet that, like so many things in the natural world, it will make our human efforts look pretty puny.