A swing pushed once per second usually oscillates once per second. But if you push it harder and at the right rhythm, it can swing three times slower: one full swing for every three pushes. Physicists call this subharmonic resonance, and it seems to govern the most prominent climate and solar oscillations.
Earth's global temperature does not rise smoothly. On top of the warming trend lie strong fluctuations: from year to year, it warms and cools by amounts comparable to the trend itself. For a long time, these swings were dismissed as noise, random disturbances. But when the smooth trend was removed from temperature data since 1880, an unexpected rhythm emerged: a peak at a period of about 3 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. This period coincides with the flip-flop phenomenon: the Sun's active longitudes alternate in dominance roughly every 3.7 years. Apparently, both phenomena draw from a single source: nonlinear resonance within the solar dynamo. Moreover, the spectrum of solar fluctuations decays exponentially with a characteristic time of 25.38 days, matching the Sun's rotation period at a latitude of 26 degrees. Chaos in the system is confirmed by a positive Lyapunov exponent (0.286 month⁻¹).
Coherence between detrended solar activity and global temperature is high for periods longer than 20 years, even though the trends do not correlate. This means the Sun and climate exchange not slow trends but fast fluctuations amplified by a shared resonance mechanism. Previously, these links were lost in noise because they were sought at the wrong frequencies.
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 fluctuates so strongly and how these fluctuations 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: the Sun's active longitudes alternate in dominance roughly every 3.7 years. This points to a common source for both phenomena.
The idea that galactic turbulence affects Earth's climate echoes Isaac Asimov's novel "The End of Eternity," where changes in distant space cause cataclysms on Earth.