tons of bone-dry biomass can be grown per year for each acre of land. These assumptions allow the committee to develop estimates of the amount of land that would be required if biomass were the feedstock for 100 percent of the hydrogen production. Figure 6-15 provides those estimates for both the current and possible future technologies, both with and without CO2 sequestration.
Figure 6-15 shows that under current technology conditions, if all of the hydrogen were generated from biomass, in 2050 the United States would be using about 650,000 mi2 of land to grow the biomass needed to fuel the light-duty fleet of vehicles. However, with the possible future technologies, the nation would need a substantially smaller amount, about 280,000 mi2. The difference between the two estimates of land use results from differences in the assumed productivity of land and differences in the efficiency of the gasifier under the two states of technology development.
For comparison purposes, the United States is estimated to have roughly 700,000 mi2 of cropland and 900,000 mi2 of rangeland or pastureland (Vesterby and Krupa, 1997). If the biomass can be grown on land that currently serves as rangeland or pastureland, which the committee believes is unlikely because of water-use restrictions, then under possible future technology conditions, by 2050 biomass production would account for about 16 percent of this land, even if all of the hydrogen were made using biomass as a feedstock. However, if the biomass requires land that currently serves as cropland, then by 2050 under possible future technology conditions, biomass production could use about 33 percent of all current cropland.
For those technologies that rely on CO2 sequestration, the committee examined the amount of CO2 that would be sequestered annually and the cumulative sequestration. The models assume that 90 percent of the CO2 for a given plant can be separated and sequestered and that 10 percent of the CO2 will escape into the atmosphere. Figures 6-16 and 6-17 respectively provide estimates of the annual and cumulative amounts of CO2 that would be sequestered with current technologies, for central station natural gas and coal plants and midsize biomass plants. Figures 6-18 and 6-19 respectively provide annual and cumulative sequestration estimates for possible future technologies.
Figures 6-16 through 6-19 show the massive amount of CO2 sequestration that would be required, both annually and cumulatively, in order to use fossil fuels as hydrogen feedstocks while sharply reducing the amount of CO2 released into the atmosphere. By 2050 the United States would need