Although not every scientist agrees, emissions of carbon dioxide from the combustion of fossil fuels, mostly petroleum, natural gas and coal are considered to be a major factor in causing the onset of global warming. Unacceptable rises in temperature are leading to rising sea levels from the melting of polar ice and the corresponding climate changes may affect plant and animal life in otherwise temperate zones.
Technological advances reduce the growth in energy demand to around 1 per cent below the rate of economic growth, but the world’s demand for energy is expected to continue to rise exponentially, particularly in respect to emerging economies such as China and India. What is needed is a number of renewable sources of energy, not limited by resource depletion (as is the case with fossil fuels) and that are “clean” in that they emit little or no so-called “greenhouse gases”. Renewable sources include wind and sea current power. However nuclear power, which is purported to meet both criteria, must be excluded, as it does not fulfil either.
Before considering alternative sources, it is necessary to understand the size of the problem by examining current global energy consumption. Energy units exhibit little uniformity, but the joule can be used as a universally acceptable basis for analysis. Big numbers have to be employed to express global energy parameters, i.e., the exajoule (joule x 1018) and the petajoule (joule x 1015), abbreviated as EJ and PJ respectively. The world’s energy consumption in 2003 was 409 EJ, of which fossil fuels provided 90 per cent as primary energy. Of this, 60 EJ was in the form of electrical energy, with only 10 EJ provided by nuclear generation.
Transport constrained to fixed guide systems, such as rail and tramways can use electrical energy directly from current collectors, but mobile transport able to move on roads or rough terrain uses mostly liquid fuels derived from oil. As oil reserves deplete, liquid fuels will be synthesised increasingly from natural gas and then coal, until all fossil fuels able to be economically extracted are exhausted.
To use electrical energy as an alternative to conventional liquid fuels for mobile transport requires the production of hydrogen from electrolysis and its subsequent cryogenic liquefaction for on-vehicle storage. This has an inherent energy penalty over the derivatives of primary fuels and of course, unless the electricity used to produce the hydrogen fuel is from a renewable and “clean” source, offers no panacea to global warming. Assuming mobile transport requires 40 per cent of global energy and taking into account the energy loss in conversion, the requirement for global electrical generation rises to 700 EJ. The problem is that electrical energy of whatever means of generation is a poor substitute for the adaptable primary energy obtained from fossil fuels.
A typical 1200 MW nuclear power (pdf file 1.55MB) plant produces 32 PJ per annum, so to provide for 700 EJ around 20,000 nuclear power stations would have to be built. To fuel this number of stations, around 4,600,000 tonnes per annum of uranium would be required.
However the emerging economies of China and India are setting the pace for growth and rising energy demand, so to meet their aspirations the initial requirement for the building of 20,000 nuclear power stations is likely to be insufficient. In reality there is little chance of fuelling the current modest building program of new stations as secondary sources of uranium are expected to be exhausted by 2012, creating a shortfall in supply unable to be filled by additional mining, so the first desired characteristic of sustainability is unattainable.
Then the claim for the carbon-free status of nuclear power proves to be false. Carbon dioxide is released in every component of the nuclear fuel cycle except the actual fission in the reactor. Fossil fuels are involved in the mining, milling and enrichment of the ore, in the fuel can preparation, in the construction of the station and in its decommissioning and demolition, in the handling of the spent waste and its re-processing and in digging the hole in the rock for its deposition.
The lower the ore grade, the more energy is consumed in the fuel processing, so that the amount of the carbon dioxide released in the fuel cycle depends on the ore grade. Only Canada and Australia have ores of a sufficiently high grade to avoid excessive carbon releases and to provide an adequate energy gain. At ore grades below 0.01 per cent for “soft” ores and 0.02 per cent for “hard” ores more CO2 than an equivalent gas-fired station is released and more energy is absorbed in the cycle than is gained in it. Ores of a grade approaching the “crossover” point such as those in India of 0.03 per cent, if used, risk going into negative energy gain if there are a few “hiccups” in the cycle.
The industry points to the presence of uranium in phosphates and seawater, but the concentrations are so low that the energy required to extract it would exceed many times the resulting energy obtained from any nuclear power.
Maybe the world does not need to stop all carbon dioxide emissions, but even a doubling of nuclear generation capacity would only provide 20 EJ, i.e., 5 per cent of world energy consumption. There is no possibility of an extension of nuclear capacity solving, to any significant degree, the problem of global warming.
It is claimed that nuclear power meets the two characteristics of sustainability and zero or low carbon dioxide emissions and so might be able to substitute for fossil fuels once they are exhausted and in the meantime avoid release of some greenhouse gases. The claims are baseless.
In conclusion, a guide to the maximum amount of carbon dioxide released from the combustion of fossil fuels can be calculated, given that they are limited. The graph shows that if economic growth continues as currently, the reserves of oil, gas and then most of the coal will have emptied by the end of the century. From a knowledge of the carbon content of the three fuels, it is then possible to work out the total amount of carbon dioxide likely to be released.
This comes out as 5 exagrams or 5,000 billion tonnes.
An earth scientist should be able to work out the likely temperature rise that the release of this limited amount, mostly over the next 50 years, is likely to produce. Before hampering the world with useless measures unable to reduce the eventual amount of the release of carbon dioxide, it would be more appropriate to estimate the ultimate consequences of today’s immoderate exploitation and exhaustion of fossil fuels.