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Because of what the rich nations are doing, lands that now grow crops will become barren, glaciers that for millennia have fed rivers will dwindle, the sea will take over fertile fields, tropical diseases will spread, and people will starve or become refugees. For at least the past twenty years, the rich countries have known that their actions risk causing these effects; and from some time in the first decade of the twenty-first century, they have known that their actions very probably will have these effects. The fact that these harms are an unwanted but unavoidable side effect of pursuing otherwise innocuous goals, like giving people the kind of lifestyle they desire, is no justification for causing such harms. According to the doctrine of double effect, knowingly causing harm can be justified if the harm is not intended, the goal is sufficiently important to outweigh the harm caused, and there is no other way of achieving the goal without causing at least as great a harm. In the case of global warming, however, the reverse is the case: the harm caused far outweighs the good obtained.
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