with its highly optimistic assumptions about the
future availability of renewables, nuclear, and CCS, the mid-century carbon
emission reduction goal could only be achieved if the annual growth in GDP per capita between now and 2050 were to slow to a
rate of 1 % per year.
The difference between Professor Nordhaus's optimal carbon tax policy and a fifty - year delay policy is insignificant economically or climatologically in view of major uncertainties in (1)
future economic growth (including
reductions in carbon
emissions intensity); (2) the physical science (e.g., the climate sensitivity); (3)
future positive and negative environmental impacts (e.g., the economic «damage function»); (4) the evaluation of long - term economic costs and benefits (e.g., the discount
rate); and (5) the international political process (e.g., the impact of less than full participation).