To first order the number of days in Summer function for apsidal precession is a constant plus a cosine function. ΔΔt, the error for the approximation, has a magnitude less than 0.0003 days.
As before θ is the angle between the Earth's perihelion and the Winter Solstice. Apsidal precession has to be considered as a contribution to global warming. If there is net annual heating due to apsidal precession then this contribution needs to be deducted before the effect of greenhouse gases can be determined. Only the change in the angle of angle of perihelion was taken into consideration and the other orbital elements were assumed to remain constant.