  We give new upper bounds on the stable commutator lengths of Dehn twists in
mapping class groups and new lower bounds on the stable commutator lengths of
Dehn twists in hyperelliptic mapping class groups. In particular, we show that
the stable commutator lengths of Dehn twists about a nonseparating and a
separating curve on an oriented closed surface of genus 2 are not equal to each
other.
