The Stacks project

Proof. (If $\mathcal{F}$ is torsion, then the vanishing follows immediately from Lemma 59.95.7.) By Lemma 59.74.5 we can write $\mathcal{F}$ as a filtered colimit of constructible sheaves $\mathcal{F}_ i$ of $\mathbf{Z}$-modules whose supports $Z_ i \subset X$ are finite sets of closed points. By Proposition 59.46.4 such a sheaf is of the form $(Z_ i \to X)_*\mathcal{G}_ i$ where $\mathcal{G}_ i$ is a sheaf on $Z_ i$. As $K$ is separably closed, the scheme $Z_ i$ is a finite disjoint union of spectra of separably closed fields. Recall that $H^ q(Z_ i, \mathcal{G}_ i) = H^ q(X, \mathcal{F}_ i)$ by the Leray spectral sequence for $Z_ i \to X$ and vanising of higher direct images for this morphism (Proposition 59.55.2). By Lemmas 59.59.1 and 59.59.2 we see that $H^ q(Z_ i, \mathcal{G}_ i)$ is zero for $q > 0$ and that $H^0(Z_ i, \mathcal{G}_ i)$ generates $\mathcal{G}_ i$. We conclude the vanishing of $H^ q(X, \mathcal{F}_ i)$ for $q > 0$ and that $\mathcal{F}_ i$ is generated by global sections. By Theorem 59.51.3 we see that $H^ q(X, \mathcal{F}) = 0$ for $q > 0$. The proof is now done because a filtered colimit of globally generated sheaves of abelian groups is globally generated (details omitted). $\square$