When well-off individuals do not offset their own personal greenhouse gas (GHG) emissions, are they acting morally wrongly? One prominent argument for thinking so is an Argument from Expected Harm. It asserts that the scale and duration of the threats posed by our current climate-affecting activities are such that, even though each of us makes only a proportionally small contribution, the expectation of harm (that is, the probability-weighted sum of the possible harms) associated with an individual’s lifetime emissions is large enough to be indefensible. Suppose you take this argument seriously, as John Broome and others urge. Then you need to consider a response to it that Broome also goes on to make: the Offsetting Response—you can offset your emitting activity by purchasing carbon offsets. When you emit, you increase the number of GHG molecules in the atmosphere. But by paying for carbon offsets, you can ‘cancel out’ your contribution. So the objection to your emissions activity generated by the Argument from Expected Harm is nullified by offsetting. Our aim in this paper is to assess the adequacy of the Offsetting Response.