Revised 29 August 2021
Minerals and fossil fuels form stocks of resources, whereas ecological systems can provide a sustainable flow of resources so long as these resources are carefully husbanded (Odum & Odum, 1976). It requires energy to mine stocks of minerals. The low hanging fruit of easily accessible and concentrated stocks of minerals are mined first. As the more concentrated stocks of minerals become depleted, more and more energy is required to mine the remaining less concentrated stocks (Bardi, 2014). The same applies to solid fossil fuels. The low hanging fruit are mined first and subsequent mining for solid fossil fuels and drilling for liquid oil or gas requires more and more energy. Ultimately continued extraction of fossil fuels from the ground will require as much energy to extract as that energy contained in the extracted energy resource (Giampietro, 2013) and there would be no sensible purpose in extracting fossil fuels for use as energy when theEROI in doing so is less than 1.0. It would still be possible to continue extracting fossil fuels from the ground for use and value as a chemical by using subsidies of extraction from other energy sources.
When the EROI of any fossil fuel source declines below that of other fossil fuel sources, continued extraction of the lower EROI source could result in greater greenhouse gas emissions to the atmosphere compared to closing down the lower EROI source and providing the same level of output from a fossil fuel source with a higher EROI. The quality of both fossil fuel sources and their greenhouse gas emissions characteristics would need to be taken into account because the exergy of the fuels can differ and some fossil fuels are dirtier than others. Ideally, lower EROI fossil fuel sources become uneconomic in dollar terms for continued extraction and these sources of energy are replaced by higher EROI sources which could be renewable energy sources. In practice this does not necessarily happen when continued extraction of lower EROI energy sources are heavily subsidised.
Continued combustion of fossil fuels for use as energy will continue to add greenhouse gas emissions to the atmosphere. Greenhouse gas emissions from a power plant can be prevented from venting to the atmosphere using technology, but at an additional energy cost of investment in plant and machinery. Ultimately, mitigation of the impact of human induced climate change requires an absolute reduction in the combustion of fossil fuels. In the absence of the use of fossil fuels for energy, we will still need to use energy to maintain an acceptable standard of living. On the surface, we have the options of transitioning from fossil fuels to renewable energy sources and/or nuclear energy, bearing in mind that nuclear energy is problematic in terms of risk and disposal of nuclear waste. Renewable energy and nuclear energy have proven to be feasible technologies, but not necessarily viable technologies in the absence of continued use of fossil fuels. Production of any technology relies on a web of supply chains which are extremely complex and difficult to unravel. Failure in any one link in any of the supply chains can result in the difference between short-term feasibility of a technology with hidden subsidies and long-term sustainable viability. It is critical that the sustainable viability of any renewable energy source is clearly established without doubt before investing materials and energy in a large scale transition from fossil fuels to renewable energy. The history of biofuels stand testimony to the risks of foolhardy expectations based on premature and inadequate energy analyses (Giampietro & Mayumi, 2009).
Transition to renewable energy sources will require an investment in replacement plant, machinery, and infrastructure, all of which involve additional consumption of materials and energy. Renewable energy sources will initially need to be subsidised by fossil fuels because these replacement energy sources alone are unable to bootstrap a transition. Bootstrapping is impossible because the energy required to invest in setting up renewable energy systems is greater than the energy flow provided by those replacement energy sources in any one year until after the energy payback period has been reached.