  Let $M$ be a complete non-compact Riemannian manifold and $\sigma $ be a
Radon measure on $M$, we study the existence and non-existence of positive
solutions to a nonlocal elliptic inequality \begin{equation*}
(-\Delta)^{\alpha} u\geq u^{q}\sigma\quad \text{in}\,\,M, \end{equation*} with
$q>1$. When the Green function $G^{(\alpha)}$ of the fractional Laplacian
$(-\Delta)^{\alpha}$ exists and satisfies the quasi-metric property, we obtain
necessary and sufficient criteria for existence of positive solutions. In
particular, explicit conditions in terms of volume growth and the growth of
$\sigma$ are given, when $M$ admits Li-Yau Gaussian type heat kernel estimates.
