Ice core data. Note length of glacial cycles averages ~100,000 years. Blue curve is temperature, green curve is CO2, and red curve is windblown glacial dust (loess).
An average of several samples of δ18O, a proxy for temperature, for the last 600,000 years
These orbital changes alter the amount of sunlight reaching the Earth by up to 25% at mid-latitudes. That has a huge effect. The term "forcing" is a physical process which definitely affects the Earth's climate.