Not all of the CO 2 remains in the atmosphere. Plants use CO 2 and return O 2 to the atmosphere. As forests are cut down, less CO 2 will be removed from the atmosphere. Periods of glaciation lasting several tens of millions of years may be explained by plate tectonics. Movement of a continent over a polar region may induce such long term glaciation.
Eccentricity refers to change in the elliptical shape of the orbit.
Note how the orbit becomes almost circular at minnimum ellipticity. Precession is the change in azimuth of Earth's tilt axis relative to the ecliptic plane. Click on the three circles at the top to review the effects of these three components. Eccentricity - the Earth's orbit changes from nearly circular to elliptical. The time between periods of maximum elliptical character is about 100,000 years.