Cloud cover causes cooling

Cloud cover causes cooling. Lack of, heating. Because, sun, shade.

Mostly, cosmic rays (the real ones, not the Fantastic Four ones) cause clouds. Stars cause cosmic rays.

When our local star gets active, we get more cosmic rays, more clouds, more cooling. When our star is more dormant, the opposite. Humans are insignificant to the process.

Cloud cover may of course also be increased by comet strikes, volcanic eruptions, and possibly a major nuclear conflict. In descending order of potential cooling.

But all these are the minor fluctuations within the larger cosmic cycle.

Every 25,000 years or so, our star orbits near other stars. We get more of their cosmic rays, and an ice age. Our long "summer" is waning. We're on our way back there now. Invest long-term in heating fuels.