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Letters to the Editor

Fortnightly Magazine - April 2005

model that set a specific, usually CO 2-equivalent reduction target over a limited number of years without consideration of whether this reduction is feasible technically and economically. Even worse are the initiatives that specify mandatory percentages of carbon-emission-free technologies, such as renewable sources for power generation and transportation fuels.

Why not let the industry make its own decisions on how to meet economy-wide reductions in greenhouse-gas intensity as a percentage of GDP? For example, the electric utility industry may find it most practical and economical to gain lead time for deployment of a truly sustainable power supply in coal-rich countries such as the United Sates, China, and India to use the advanced IGCC process modified for hydrogen production by catalytic water gas shift and CO 2 removal and sequestration. It can be demonstrated easily that the land requirements for biomass to replace fossil fuels far exceed what is available in the world and the United States, including croplands, pastures, and meadows. 1 Moreover, the progress of reducing greenhouse gas emissions by major segments of industry through voluntary profitable technology improvements suggests that we may all be surprised by how readily the United States could comply with an economy-wide 2.4 percent annual reduction in greenhouse-gas intensity measured in metric tons of CO 2-equivalents of the GDP in constant 2004 dollars without any specific requirements for how to accomplish this. Political bodies are clearly the least qualified and most biased arbiters of which areas of the economy and which energy sources and technologies would offer a least-cost path.

I want to close with an endorsement of a global initiative patterned on the findings of the U.N. Intergovernmental Panel on Climate Change (IPCC). 2,3 These findings call for a stabilization of atmospheric CO 2 concentration at 550 parts per million by volume (ppmv), about double the pre-industrial concentration of 280 ppmv. This would require capping cumulative anthropogenic carbon emissions between 1990 and 2100 at 1,000 billion metric tons (gigatonnes) and thereafter would limit them to the level of natural sequestration-currently about 4 gigatonnes/ year. Eventually, additional average global surface temperature increases at median climate sensitivity would stabilize at 1.6-2.8°C-still in the range of natural climate variations during the past 10,000 years. It is true that during the past 160,000 years, which includes the last 100,000-year ice age and the preceding and following interglacial periods, CO 2 concentrations did not exceed 300 ppmv, but average global surface temperatures varied from 2°C above those at the beginning of the 20th century to 10°C below them without human intervention. Nevertheless, it seems prudent not to conduct a global experiment of the effect of more than doubling of the pre-industrial CO 2 concentrations. The theoretical effect of the resulting radiative forcing of 4.4 watts/square meter is a 1.2°C increase in the effective emission temperature of the Earth of -18°C, 5.5 kilometers up in the troposphere. 4

This compares with an average global surface temperature of +15°C. The 33°C difference (a lapse rate of 6°C/kilometer) is due to the benign effect of the major greenhouse gas-water vapor, which