  Observations of protoplanetary disks suggest that the gas and dust follow
significantly different radial distributions. This finding can be theoretically
explained by a combination of radial drift and gas drag of intermediate-sized
dust grains. Using a simple parametric model to approximate the different
distributions of the gas and dust components, we calculate and examine the
impact of radial drift on the global dust temperature structure. We find that
the removal of large grains beyond the "truncation radius" allows this region
to become significantly warmer from reprocessed stellar radiation shining down
from the disk upper layers, increasing the outer disk temperature by
$\sim10-30\%$. This change is sufficient to raise the local temperature to a
value exceeding the CO desorption temperature. These findings imply that the
disk density structures induced by radial drift are able to create multiple CO
snow-lines. The inner disk CO is in the gas phase, freezing out near the
classical snow-line at $R\sim20-40$ AU. Moving outward, the CO sublimates once
again beyond the truncation radius (80 AU in our models) and subsequently
re-freezes out at sufficiently large stellar distances, beyond
$R\gtrsim130-200$ AU. We find that thermal desorption of CO in the outer disk
becomes competitive with external UV photodesorption and that this additional
transition from solid state CO to the gas-phase has significant implications
for the C/O ratio in the outer disk.
