While many, not all, actions to reduce emissions may be costly today, their benefits will only accrue several decades from now. If the discount rate is zero, a benefit of USD 1 billion in 2050 would justify an equivalent investment in emissions reductions today of USD 1 billion. However, if the discount rate is 5% per year, today only an investment of USD 200 million would be justifiable. It would fall to USD 43 million at an, admittedly very high, discount rate of 10%.