The Paris Agreement aims to keep the increase in global average temperature
\[
\boxed{\text{well below }2^\circ\text{C}}
\]
above pre-industrial levels while pursuing efforts to limit warming to
\[
\boxed{1.5^\circ\text{C}.}
\]
Hence,
\[
\boxed{1.5^\circ\text{C} - 2^\circ\text{C}}
\]
is the correct answer.
Therefore,
\[
\boxed{(C)}
\]