Which of the following is not related to the astronomical theories of climate change?

The correct answer is D) Solar irradiance. The astronomical theory of climate change is the Milankovitch theory, which explains glacial-interglacial cycles through changes in the way Earth moves around the Sun. It has three parameters: eccentricity, obliquity and precession.

• A) Eccentricity of Earth's orbit: This is the shape of the orbit, which varies between nearly circular and more elongated over about 100,000 years. It is a Milankovitch parameter, so it is related.
• B) Obliquity of Earth's axis: The tilt of the axis varies between about 22.1 and 24.5 degrees over roughly 41,000 years. This changes the seasonal contrast, so it is related.
• C) Precession of equinoxes: The wobble of the axis, with a cycle of about 23,000 years, changes which season falls at perihelion. It is related.
• D) Solar irradiance: This is the output of the Sun itself, a solar or extraterrestrial factor. It is not an orbital or rotational parameter, so it is not part of the astronomical theory in the UPPSC sense.

Core concept: Milankovitch cycles, which link orbital geometry to insolation and ice ages. In Mains, this supports answers on paleoclimate and on why the current warming trend cannot be explained by orbital forcing alone.

Trap: Aspirants sometimes pick solar irradiance because it sounds like an astronomical factor. Stick to the three orbital parameters for this question.