A swing pushed once per second usually swings once per second. But if you push harder and at the right rhythm, it can go three times slower: one swing for every three pushes. This effect is called subharmonic resonance. It turns out that this very effect drives the most noticeable oscillations of climate and the Sun.
Earth's global temperature does not rise smoothly. On top of the warming trend lie strong oscillations: from year to year it warms and cools by amounts comparable to the trend itself. When the smooth trend is removed from temperature data since 1880, a rhythm emerges in the residual: a peak at a period of about three years. Three years is one-third of the annual cycle that Earth's orbit around the Sun imposes. So the climate responds to the yearly "push" three times slower than it is pushed.
Solar activity follows the same rule. After removing the 11-year cycle from sunspot data, a peak remains at 3.7 years. And in Antarctic ice cores, a cycle of 15 thousand years is found, which is one-third of the precession period of Earth's axis. The same mechanism works at all scales, from years to millennia.
Now that a common rhythm has been found, climate models can incorporate nonlinear interactions instead of linear trends. This will not make weather forecasts accurate years ahead, because chaos limits predictability, but it will help explain why climate oscillates so strongly and how these oscillations relate to the Sun. The swing that oscillates three times slower than it is pushed turns out to be common across the entire solar system.
The 3.7-year period found in solar activity coincides with the period of the so-called flip-flop phenomenon: active longitudes on the Sun change dominance roughly every 3.7 years. This points to a common source for both phenomena.
The idea that galactic turbulence influences Earth's climate echoes Isaac Asimov's novel 'The End of Eternity,' where changes in distant space cause cataclysms on Earth.