Daniel W. answered • 06/06/19
Kind and Knowledgeable English, Latin, and Theatre Tutor
The type of irony here is dramatic irony, which occurs when the audience knows something that a character onstage does not.
In this case, Macduff has left Scotland to find Malcolm in England so that he can convince him to overthrow Macbeth. What neither of them know is that in the previous scene, the audience witnessed the murder of Macduff's entire family on Macbeth's orders. So when Macduff is describing how terrible Macbeth's rule is and says "Each new morn / New widows howl, new orphans cry, new sorrows / Strike heaven on the face," he does not realize that he himself is now a widower too.
Meanwhile, Malcolm is not sure whether to believe Macduff, thinking he might be on Macbeth's side and trying to lure Malcolm back to Scotland to be killed. So Malcolm points out that Macduff was once loyal to Macbeth, and that Macbeth has not harmed him yet: "This tyrant, whose sole name blisters our tongues, / Was once thought honest. You have loved him well. / He hath not touched you yet." Of course, the irony is that Macbeth has killed Macduff's family, and the news simply hasn't reached them yet--which it will by the end of the scene.
