Precession, which decides whether the Earth is closer to the sun in July or in January, is on a 23,000 - year cycle;
obliquity, which decides
how tilted the axis of the Earth is and therefore
how warm the summer is, is on a 41,000 - year cycle; and eccentricity, which decides
how rounded or elongated the Earth's orbit is and therefore
how close to the sun the planet gets, is on a 100,000 - year cycle.