Comments and Discussion

Richard N. Cooper: I agree strongly with the main conclusion of this paper by Klaus Lackner and Jeffrey Sachs, which is that there is no shortage of energy on the horizon. The paper rightly emphasizes the substitution possibilities among different forms of energy, even at today's technology, and the abundance of total energy. The debate over the prospective exhaustion of liquid fuels takes many forms, but most are based on false premises, as the paper usefully points out. The authors also argue that the world faces a serious problem in climate change, or, as they put it more generally, in the environmental constraints on energy use, and that it must be dealt with as quickly as possible. Furthermore, solutions are actually at hand with existing technology or are within reasonable sight, so there is some basis for dealing with the problem.

The paper is an unusual one for a Brookings Papers panel. It is largely a primer on the role of energy in modern society, with a main emphasis on technology and technological possibilities. There is a fair amount of catalytic chemistry here, and some physics as well. Readers will have to brush up on their high school chemistry.

The paper performs a great service in being quantitative. This is, after all, essentially a quantitative topic. One cannot talk sensibly about energy alternatives without quantifying the possibilities. There are many attractive ideas out there, such as wind power, but when one looks quantitatively at the possibilities for mobilizing them, it is clear that many can play only a niche role. The authors' focus on magnitudes is thus very useful in dispelling some myths or, more accurately, some wishful thinking. In this connection, however, I missed a more complete discussion of one potentially important technology, namely, the making of liquid fuel from biomass, both biomass grown for the purpose (and thus competing for land with food producers) and, more important, waste biomass such as corn stalks.

The intellectual framework of the policy parts of the paper involves stipulating some ceiling for atmospheric greenhouse gas concentrations, mainly CO₂. This threshold is not specified but is assumed to lie somewhere between two and three times the preindustrial concentration of about 280 parts per million. Thus the authors explicitly reject a cost-benefit approach to climate change, such as that developed by William Nordhaus, in effect assuming that the costs of climate change (and hence the benefits of mitigating it) become infinite beyond the ceiling. This assumption, I suspect, drives their call for early action.

The paper constructs a baseline, "business-as-usual" scenario for greenhouse gas emissions over the next century on the basis of an assumed convergence of income per capita around the world on income per capita (or some fraction thereof) in the United States, which itself continues to grow: the gap is narrowed at a steady pace of 2 percent a year. This does not sound unreasonable until one realizes that, along with the authors' other assumptions, it implies a growth in global income per capita of 3 percent a year until 2050. This compares with 2.1 percent a year during the half century 1950-2000. On historical experience, then, 3 percent is implausibly high. The implausibility is increased by using purchasing power parity (PPP) to calculate national and hence global GDP, so that the starting point is gross world product of $46 trillion in 2002, instead of the $31 trillion measured at market exchange rates. PPP, which, in effect, values output everywhere in the world at U.S. prices, gives much greater weight to agricultural output than does pricing at market exchange rates. Since agriculture, which accounts for a large share of output in poor countries, typically grows more slowly than other sectors, giving it greater weight implies lower growth rates than the world is accustomed to. And calculated over a century, or even half a century, even small differences in growth rates can make a big difference. Applying the authors' assumed energy elasticity of 0.55 to a more reasonable annual growth in world income per capita of 1.8 percent (implying...