Ralph M. Rotty

Atmospheric carbon dioxide: Possible consequences of future fossil fuel use

Abstract Accurate and regular measurements of the concentration of CO2 in the atmosphere during the past 20 years show an accelerating increase. Although clearing of tropical forests has released large amounts of carbon to the atmosphere, evidence is strong that a major contributor is the combustion of fossil fuels. Future energy demands of the world will require extensive further exploitation of fossil fuels, and projections show that without major development of nonfossil fuel alternatives, the atmospheric concentration will double within the next 75 years. Four issues require serious attention: The developing countries will require vastly increased amounts of energy. Major efforts to develop suitable (inexpensive) non-fossil energy sources to meet at least a portion of this demand are required. The distribution of carbon released from fossil fuels and from other anthropogenic sources among the reservoirs of the carbon cycle must be better defined. Uncertainties regarding the effect of the increased concentration of CO2 in the atmosphere on global climate must be reduced. Possible political and social responses to a substantial climate change must be studied in order to more fully understand all of the implication of increased atmospheric CO2.

Fossil Fuel Combustion: Recent Amounts, Patterns, and Trends of CO2

Several types of human activity have introduced perturbations that impinge on the natural global carbon cycle. During the past century or so, one of the major perturbations has been the release of carbon from long-term storage through the combustion of fossil fuels. During the next 100 years fossil fuel use will almost certainly be the major source causing increased levels of CO2 in the atmosphere.

Constraints on Fossil Fuel Use

The exponential growth of fossil fuel use over recent decades has resulted in a 4.3 percent annual increase in the carbon dioxide emitted to the atmosphere. The question addressed here is: When (and to what extent) will constraints limit the use of fossil fuels and the subsequent production of CO2? We discuss three types of possible constraints: resource constraints, fuel demand constraints, and environmental constraints. An analysis of the next 50 years suggests that resource constraints will not provide severe limits. The impacts of atmospheric carbon dioxide will not reach levels that cause mankind to take action soon. Fuel-demand constraints will probably limit the use of fossil fuels to levels that keep the atmospheric carbon dioxide concentration below 450 ppm(v) for the next 50 years. In spite of this conclusion we see a continuing, long term problem and urge that full efforts be made to understand and continually monitor the CO2 problem and to be alert to any changes that may require action.

How long is coal's future?

Nearly all scenarios for future U.S. energy supply systems show heavy dependence on coal. The magnitude depends on assumptions as to reliance on nuclear fission, degree of electrification, and rate of GNP growth, and ranges from 700 million tons to 2300 million tons per year. However, potential climate change resulting from increasing atmospheric carbon dioxide concentrations may prevent coal from playing a major role. The carbon in the carbon dioxide produced from fossil fuels each year is about 1/10 the net primary production by terrestrial plants, but the fossil fuel production has been growing exponentially at 4.3% per year. Observed atmospheric CO2 concentrations have increased from 315 ppm in 1958 to 330 ppm in 1974 - in 1900, before much fossil fuel was burned, it was about 290–295 ppm. Slightly over one-half the CO2 released from fossil fuels is accounted for by the increase observed in the atmosphere; at present growth rates the quantities are doubling every 15–18 years. Atmospheric models suggest a global warming of about 2 K if the concentration were to rise to two times its pre-1900 value - enough to change the global climate in major (but largely unknown) ways. With the current rate of increase in fossil fuel use, the atmospheric concentration should reach these levels by about 2030. A shift to coal as a replacement for oil and gas gives more carbon dioxide per unit of energy; thus if energy growth continues with a concurrent shift toward coal, high concentrations can be reached somewhat earlier. Even projections with very heavy reliance on non-fossil energy (Neihaus) after 2000 show atmospheric carbon dioxide concentrations reaching 475 ppm.

Past and future emission of CO2.

Although the coarse estimates given here are not nearly as precise as the data supplied to the discussion by the atmospheric, oceanographic and geophysical sciences, they might well be relevant. The estimates for net releases of C from tropical vegetation and soils are, without exception, conservative, but still add up to several 1015 g/year. Even large errors in some of the estimates could hardly modify the overall conclusion that tropical land ecosystems are a net source of C for the atmosphere at present, their activity probably amounting to 30-80% of the annual release from fossil fuels. Likewise, it is probable that land ecosystems in other parts of the world (including fresh-water and estuarine ecosystems) are acting as net sinks. The amount removed from the atmosphere by these is even more difficult to estimate. From the evaluation of ecological data alone one is tempted to conclude that terrestrial sinks cannot fully compensate for the total quantity released by terrestrial sources so that, in accordance with the second hypothesis mentioned at the beginning, land ecosystems as a whole are a net source of C for the atmosphere. However, the possibility that releases and withdrawals are nearly balanced on a worldwide scale, as required by atmosphere781

Growth in global energy demand and contribution of alternative supply systems

Growth in global energy demand since the end of World War II has been nearly constant at a rate of 5.3% each year. When energy demand is projected into the future, the basic question is how long such an exponentially growing global energy use can continue, and a more accurate analysis than projecting exponential growth indefinitely into the future is certainly desirable.

Greenhouse gases in the atmosphere: what do we know

In addition to carbon dioxide there are a number of gases (e.g., N/sub 2/O, CH/sub 4/, CF/sub 2/Cl/sub 2/, CFCL/sub 3/, etc.) which could affect the radiation balance of the earths atmosphere. Recent measurements indicate that the atmospheric concentrations of these gases are increasing. Incomplete understanding of the sources, sinks, and/or chemical interactions of these gases in the atmosphere makes it difficult to relate human activities to future concentrations and to climatic effects. Atmospheric modeling suggests that during the past decade the trace gases should have had a warming effect that was half as much as CO/sub 2/. To illustrate the magnitude and complexity of the human involvement, the authors reviewed the budget of N/sub 2/O in the atmosphere. Anthropogenic production of N/sub 2/O occurs primarily in the combustion of fossil fuels and in the use of nitrogen fertilizers but acid rain, sewage treatment, electric power transmission, forest clearing, and other activities all impact the global N/sub 2/O budget. Although estimates of N/sub 2/O sources are subject to large uncertainty, the total anthropogenic contribution may be approaching 50% of the natural releases.

Uncertainties associated with global effects of atmospheric CO2

Abstract Although the evidence is quite clear that the increase in atmospheric CO2 is at least to a large degree a result of fossil fuel burning, and it is equally clear that this increase will result in some change in the global climate, there are quantitative uncertainties that require additional understanding before full assessments can be made. There are quantitative uncertainties in the natural carbon cycle as well as uncertainties in the behaviour of the various reservoirs when perturbed by man. There are questions about the terrestrial biosphere and about the rate at which the oceans can assimilate and store carbon. There are uncertainties in regard to the climate change that can result from increased atmospheric CO2. Progress in modelling the atmosphere must continue to narrow these uncertainties before the impacts of climate change on man can be adequately determined. The future demands for fossil fuels are uncertain. The growth of the developing world will be closely linked to fossil energy for the next five to eight decades, and rates of growth in these world segments are dependent on many ill-defined quantities. Only the observed increase in the atmospheric concentration and the present (and recent past) rate of production of CO2 from fossil fuels provide data without uncertainties.

The question mark over coal: Pollution, politics, and CO2

Abstract There is a growing concern about the effect of fossil-fuel burning, and the consequent increase in carbon dioxide (CO 2 ) concentration in the atmosphere. This increasing concentration is now well-documented, and although the evidence of actual or potential climate changes is not conclusive, the growth in energy consumption magnifies the importance of the possible dangers. This article highlights two aspects of the issue. The CO 2 increase will be mainly produced by coal. And whereas the increase in atmospheric CO 2 is now being imposed upon the world principally by the USA, the USSR, and Western Europe, the developing countries will probably be important contributors by early in the next century. Using world energy resource estimates and projections of the global production of CO 2 from fossil-fuel burning in the year 2025, the authors argue that it will be difficult to achieve an international consensus and commitment to deal with the issue. This is because of the relationship between economic growth, industrialisation, and the production of CO 2 , and because of the distribution of the beneficial and harmful effects of any climatic change.

Use of Energy Scenarios in Addressing the CO2 Question

A reference scenario for CO2 emissions was developed using a model of world energy supply and demand. In the reference scenario, world GNP and world energy demand increase at average rates of 2.1 percent per year and 1.5 percent per year, respectively during the period 1975-2100. The corresponding annual CO2 emissions rise to a maximum of 16 gigatons of carbon around 2050 and then decline as a result of a transition to nonfossil fuel energy systems. A modified scenario for high CO2 emissions was obtained by assuming an abundant supply of low cost coal, thus eliminating the transition. A low case was developed in which the low cost of alternative energy (i.e., solar, nuclear) induces an earlier shift away from fossil fuels. Annual emissions of the three scenarios were used as input to a global carbon cycle model and the CO2 buildup in the atmosphere during the period 1980-2100 was determined by the model. All three scenarios showed continuous rises in atmospheric CO2 concentration. The reference scenario r...