ABSTRACT
Each of us ought to avoid emitting greenhouse gas. We have a moral duty not to harm other people, and particularly not to do so for our own benefit. The greenhouse gas we emit spreads around the world and contributes to global warming, which is harmful. Emitting greenhouse gas harms people by this means, so morality requires us not to do it. True, there are exceptions to the duty not to harm other people. You may harm someone in self-defence, for example. It is sometimes claimed that there is an exception when the harm is trivial; it is said to be morally permissible to do trivial harms to other people if it brings you significant benefits. That may be so. But the harm done by an individual’s greenhouse gas emissions is not trivial. They do only a very little harm to each person, but added up over everyone it amounts to a significant harm. I estimate that the gas each of us emits during our lifetime will shorten people’s lives in total by a few months. This is not trivial. So the harm done by greenhouse gas does not fall under the triviality exception, if there is one, and nor does it fall under any of the other exceptions to the duty not to harm. Morality does indeed require us not to emit greenhouse gas. I recommend you to meet this duty by reducing our emissions and offsetting any that cannot be eliminated. The moral duty not to harm other people is a duty of justice. This means we owe it to people, as individuals, not to harm them, and they have a right not to be harmed by us. Besides moral duties of justice, we also have moral duties of beneficence (Broome 2012). These are duties to make the world better and not worse, so far as we can. In emitting greenhouse gas, we are probably also failing in a duty of beneficence, because our emissions probably make the world worse on balance, and we could reduce them. You might think the duty of justice to avoid doing harm is merely a part of the duty of beneficence, because to make the world better you must avoid doing harm. But actually the duty of justice is distinct. Sometimes you should avoid doing harm even if you do it in order to make the world better on balance. This is shown by a well-known example invented by Judith Thomson (1985): a surgeon has in her hospital five patients, each needing an organ transplant.
