Normally the pitcher who allows a runner to reach base is charged with the run if the runner eventually reaches home, even if the pitcher is replaced before the runner scores. If the run is an earned run, that pitcher's ERA is affected.
Now that MLB is placing a runner on second base at the start of each team's at bat in extra innings. (This was already being done in the minor leagues for a few seasons prior to MLB adopting the practice.) That runner is either the last batter of the previous inning or a substitute for that batter. Either way, the pitcher did not allow the runner to reach base. Thus the question: How does it affect a pitcher's ERA if the automatic runner scores?