In Climate Matters (2012), John Broome argues that individuals have private duties to offset all emissions for which they are causally responsible, grounded in the general moral injunction against doing harm. Emissions do harm, therefore they must be neutralized. I argue that individuals' private duties to offset emissions cannot be grounded in a duty to do no harm, because there can be no such general duty. It is virtually impossible in our current social context―for those in developed countries at least―to do no harm, and we cannot have duties to do what we cannot do. I argue that this shifts the general injunction from 'do no harm' to 'do the least harm', and thereby reopens the question of tradeoffs which Broome had set aside as a matter of 'goodness' rather than 'justice'. He admits that when it comes to goodness, reducing emissions is not the best way to promote the good. The focus of this paper is on whether when it comes to minimizing injustice, reducing emissions is the best way. Climate change is undoubtedly one of the most important issues we face; it's clear that it matters prima facie. The question is whether―and to what extent―it matters all-things-considered.