Why is CO_2 a nonpolar molecule, whereas CO is a polar molecule?

The $C - O$ bond in both gases is polar to a certain, limited extent. ""^(+delta)C-=O^(delta-) has some polarity; on the other hand, for ""^(delta-)O=^(delta+)C=O^(delta-), the vectors of the bond dipoles clearly sum to ZERO.
This polarity is not reflected in the boiling points of the 2 gases, $- {191.5}^{\circ}$ for $C O$ at $1 \cdot a t m$, versus a normal sublimation point of $- {78}^{\circ} C$ for carbon dioxide, however, carbon dioxide is a bigger molecule, with extra dispersion forces.