We face tight bounds on our choices regarding climate change. Given the level of past emissions and likely limits on temperature increases, we have used up most of the flexibility that we might have once had. Keeping temperatures below reasonable limits requires transforming our energy system, a process that is likely to be slow because of the sheer size of the system. If we start now and go as quickly as possible, we will still have a hard time keeping temperature increases to a reasonable level. This applies on a global basis. Emissions have to be reduced to zero or near zero in the not too distant future, which means that all countries have to reduce. One of the keys is installing clean energy in the developing world in the first place rather than locking in a fossil fuel infrastructure, which will then either lead to excessive temperature increases or have to be scrapped.
These policy conclusions have important implications for ethical arguments and justice as applied to climate change. They tell us where policies based purely on self- interest—a desire to stop hitting ourselves in the head with a hammer—take us. They take us to aggressive reductions in emissions. The more serious and more immediate the problem of climate change, the more self-interest will lead to aggressive policies. Claims that following our selfinterest leads to terrible outcomes or moral corruption do not understand what is in our self-interest.
The outer bounds of reasonable climate policies act also as constraints on ethics. Policies that do not stay within the bounds risk serious harms. In particular, any policy that does not require emissions reductions by all nations in the not-too-distant future will violate basic imperatives to avoid serious harms from climate change. This means that policies like the Berlin Mandate and the Kyoto Protocol should be rejected. If ethical arguments lead us to policies of this sort, they too should be rejected.