Milankovitch cycles
Climate forcing caused by variations in solar irradiance have occurred during Milankovitch cycles, which span periods of about 40,000 to 100,000 years. Milankovitch cycles consist of similarly long-duration cycles in Earth's orbital eccentricity (or ellipticity), orbital obliquity, and tilt direction. Among these, the 100,000 year cycle in eccentricity causes TSI to fluctuate by about +/-0.2%. Currently, Earth’s eccentricity is nearing its least elliptic (most circular) causing average annual TSI to very slowly decrease. Simulations also indicate that Earth's orbital dynamics will remain stable including these variations for least the next 10 million years.