Bridging the Carbon Gap: Fossil Fuel Use for the 21st Century
1:2, and natural gas only 1:4. 20, 21
Natural gas is the ideal transition fuel for power and hydrogen generation and other energy needs. 22, 23, 24 Many new, more efficient technologies are being developed and commercialized for using liquid petroleum fuels in surface and air transport. Fortunately, the carbon content of the 20,000 trillion cubic feet (Tcf) of technically recoverable and currently commercial resources of natural gas (about four times the proved reserves) is only 290 gigatonnes. The 3,000 billion barrels of technically recoverable crude oil and natural gas liquids (about three times the proved reserves) carry a carbon content of only 340 gigatonnes (see Tables 1 and 2). 25, 26, 27 Thus, the upper limit of carbon emissions of these hydrocarbon fuels is only 630 gigatonnes-well below the 1,000 GtC cumulative 1991 to 2100 anthropogenic carbon emission constraint assumed in my recommended plan to stabilize atmospheric CO 2 concentrations at 550 parts ppmv. In fact, a 630-gigatonne emission level would fall below even the more strict limit of 650 GtC required for a stabilization level of 450 ppmv.
Nevertheless, a reliance on natural gas, oil, and natural gas liquids implies a phasing out of the use of the most abundant but most problematic fossil fuels-coal and lignite. And it is doubtful that relying primarily on these less-abundant hydrocarbon fuels will provide a sufficient lead time to develop and deploy a carbon-emission-free and sustainable global energy system.
Instead, we must also find cost-effective, carbon-emission-free technologies to utilize the 1.1 to 1.8 trillion short tons of proved reserves of coal and lignite, and about seven trillion short tons of technically recoverable resources, which contain 700 to 1,100 and 4,500 gigatonnes of carbon, respectively (see Tables 1 and 2).
But with these uncertainties in the required lead time to bridge the Carbon Gap, a peak in emissions of about 12 GtC/year, between 2030 and 2040, seems to be unavoidable under the moderate goal of 1,000 GtC cumulative emissions and 550 ppmv CO 2 concentration by 2100. 6 (The more stringent case of 650 gigatonnes of carbon emissions and a 450 ppmv CO 2 concentration would imply a peak rate of 10 GtC/year carbon emissions in about 2025.)
These prospects make it imperative to arrive at an early confirmation of the economic and technical feasibility of the coal-fired power generation coupled with CO 2 separation and sequestration. A second point to confirm is an updated assessment of the economically recoverable North American and global natural gas resources to determine how much lead time they could provide in conjunction with more efficient use of economically recoverable liquid petroleum resources. And third, in parallel, it seems prudent for the United States and other industrial countries to resume and/or accelerate nuclear breeder reactor development as a baseload power back-up for the most promising renewable power technologies.
Coal Gasification To Gain Lead Time
A promising alternative would be to gasify coal and lignite to hydrogen, and use this hydrogen as the transition fuel for central and distributed power generation, and surface and air transport. The CO 2 produced