levels, then a little over 1°C of temperature increase will occur by the year 2100, but the increase will eventually level off. If fossil fuel fuel use decreases, the temperature increase during the 21st century will be fairly small, and temperature will eventually level off to its pre-industrial value. Keeping in mind the somewhat optimistic nature of these models, a 1% annual decrease in fossil fuel use was chosen as a basis for comparison with projections of future world energy needs. This 1% annual decrease can be thought of as a constraint on fossil fuel use that is necessary to avoid a serious alteration of the Earth's climate. Projection of Future World Energy Demand In order to compare constraints on fossil fuel energy production with world energy demand, a projection was done using a computer model. The model used here is the Oak Ridge long term global energy-CO2 model, developed by Edmonds and Reilly7 of the Institute for Energy Analysis of Oak Ridge Associated Universities; it provides assessments of the CO2 emissions due to fossil fuel use, as well as a host of vital information regarding the world economy's many possible scenarios.13 The computer model divides the world into nine different regions mentioned earlier, based on their energy resources and reserves, economic and technical compatibility, social similarities, and geographic proximity. Five benchmark years are chosen for the projections, which start in 1975: 2000, 2025, 2050, 2075, 2100. For each of these periods, the model sets up a balance between total energy demand and energy supply, giving as a result the projected CO2 emissions. This is done through four interacting modules: Supply, Demand, Balance, and Emission. The Supply module works on such data as the price of extraction of the primary fossil fuels: oil, coal, and gas; and the prices of transportation, refining, and production of electricity from the above. These are used to forecast a market price for each of the benchmark years and for each of the regions. In addition, production of energy through terrestrial solar, nuclear, and hydroelectric power is calculated. The Demand module uses such information as population growth and technology improvement parameters to forecast regional and global GNP, and, therefore, the energy demand. If the projected total supply and demand for a particular period do not match, the Balance module perturbs the initial input prices until global balance is obtained. The calculation of carbon emissions, once the production of fossil fuels is known, is carried out by the Emission module through the use of fuel-burning coefficients. The four modules work on a pre-specified set of data, which are often specified for each of the six forecast periods and for each of the nine areas mentioned above, and that can be changed with the aid of a computer editor. A default set of such data, contained in the model version we have been using, has permitted us to perform a basic run of the program and to obtain valuable information. In particular, we were interested in world energy demand as well as GNP per capita projections. The results are shown in Figures 6 and 7. In Figure 6, energy demand (in gigajoules per year) is plotted versus time (years), starting from 1990. We have plotted the total demand for fossil fuels (oil, gas, and solids), together with the
RkJQdWJsaXNoZXIy MTU5NjU0Mg==