How about, every 12,000 years or so the Sun micro-nova's and the ensuing output blasts the Earth a bit farther away from the Sun.
You mention 12,000 years.
This corresponds to the Milankovitch Cycles.
12,000 years from now the Northern Hemisphere will experience summer in December and winter in June because the axis of the earth will be pointing at the star Vega instead of its current alignment with the North Star or Polaris. This seasonal reversal won't happen suddenly but the seasons will gradually shift over thousands of years.
Astronomer Milutin Milankovitch* developed the mathematical formulas upon which these orbital variations are based. He hypothesized that when some parts of the cyclic variations are combined and occur at the same time, they are responsible for major changes in the earth's climate (even the ice ages). Though he did his work in the first half of the 20th century, Milankovich's results weren't proven until the 1970s.
The small changes set in motion by Milankovitch cycles operate separately and together to influence Earth’s climate over very long timespans, leading to larger changes in our climate over tens of thousands to hundreds of thousands of years. Milankovitch combined the cycles to create a comprehensive mathematical model for calculating differences in solar radiation at various Earth latitudes along with corresponding surface temperatures. The model is sort of a climate time machine: it can be run backward and forward to examine past and future climate conditions.
It was Milutin Milankovitch's belief that obliquity** was the most important of the three cycles for climate, because it affects the amount of insolation in Earth’s northern high-latitude regions during summer (the relative role of precession versus obliquity is still a matter of scientific study).
He calculated that Ice Ages occur approximately every 41,000 years. Subsequent research confirms that they did occur at 41,000-year intervals between one and three million years ago. But about 800,000 years ago, the cycle of Ice Ages lengthened to 100,000 years, matching Earth’s eccentricity cycle. While various theories have been proposed to explain this transition, scientists do not yet have a clear answer.
Milankovitch’s work was supported by other researchers of his time, and he authored numerous publications on his hypothesis. It wasn’t until about 10 years after his death in 1958 that the global science community began to take serious notice of his theory. In 1976, a study in the journal Science by Hays et al. using deep-sea sediment cores found that Milankovitch cycles correspond with periods of major climate change over the past 450,000 years, with Ice Ages occurring when Earth was undergoing different stages of orbital variation.
A 1976 study, published in the journal
Science examined deep-sea sediment cores and found that Milankovitch's theory corresponded to periods of climate change. Indeed, ice ages had occurred when the earth was going through different stages of orbital variation.
* The Serbian astrophysicist Milutin Milankovitch is best known for developing one of the most significant theories relating Earth motions and long-term climate change. He dedicated his career to developing a mathematical theory of climate based on the seasonal and latitudinal variations of solar radiation received by the Earth.
** Obliquity: axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its equitoria
l plane and orbital plane. It is different from orbital inclination.
See:
- Hays, J.D. John Imbrie, and N.J. Shackleton. "Variations in the Earth's Orbit: Pacemaker of the Ice Ages." Science. Volume 194, Number 4270 (1976). 1121-1132.
- Lutgens, Frederick K. and Edward J. Tarbuck. The Atmosphere: An Introduction to Meteorology.
- https://www.britannica.com/biography/Milutin-Milankovitch