"Climate change is often seen as an issue of intertemporal consumption trade-off: consume all you want today and face future climate damages, or sacrifice consumption today to implement costly climate policies and avoid future climate damages. When assuming enduring technological progress, a controversial conclusion ensues: to reduce intergenerational inequalities, we should postpone climate policies and let future, richer generations pay. However, the trade-off is more complex: abrupt, extreme, irreversible changes to the climate may cause discontinuities to socio-economic systems, possibly leading to a decline of human population and consumption per capita. The most relevant trade-off would then be between present consumption and the size of future generations. We show that when accounting for a very small risk of catastrophic climate change, stringent climate policies that postpone the catastrophe are optimal. Our results conform with the well-known conclusion that tight carbon budgets are preferred when intergenerational inequality aversion is low. However, by contrast with previous studies, we show that stringent policies are also optimal when inequality aversion is high, as it makes the scenario of a small and poor population unattractive. Views from opposite sides of the ethical spectrum in terms of inequ"ality aversion thus converge and warrant immediate climate action.

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