implications
In conclusion, the EROI for the world's most important fuels, oiland gas, has declined over the past one to two decades for all nations examined. It remains possible that the relatively high EROI values for the natural gas extracted during, and often used for, the production of oil may mask a much steeper decline in the EROI ofoil alone. Declining EROI is probably already having a large impacton the world economy (Murphy and Hall, 2010;Tverberg, 2012).
As oil and gas provide roughly 60–65% of the world's energy, this will likely have enormous economic consequences for many national economies. Coal, although abundant, is very unevenly distributed, has large environmental impacts and has an EROI that depends greatly on the region mined. A general decline in the energy content of US coal resource over time may be compensatedby a shift from energy-intensive underground mining of relatively high quality (but declining) Eastern US coal resources to lower-cost surface mining of lower energy-content Western US coalr esulting in no clear trend in EROI for coal.
The decline in EROI among major fossil fuels suggests that in the race between technological advances and depletion, depletion is winning.
Past attempts to rectify falling oil production i.e. the rapid increase of drilling after the 1970 peak in oil production and subsequent oil crises in the US only exacerbated the problem by lowering the net energy delivered from US oil production (Halland Cleveland, 1981).
Increasing prices, thought by most econo-mists to negate depletion through increasing incentives for exploitation, cannot work as EROI approaches 1:1, and even now has made oil too expensive to support the high economic growth it once did.
It would be tempting, from a net energy perspective, to recommend that we replace fossil fuels with renewable energy technologies as the EROI for fossil fuel falls to a level where these technologies become competitive. While EROI analyses generate numerical assessments using quantitative data that include many production factors, they do not include other important data such as climate change, air quality, health benefits, and other environ-mental qualities that are considered “externalities” to these ana-lyses.
The energy intensive carbon capture and sequestration (CCS) required to reduce fossil fuel emissions to levels equivalent withthat of wind or PV electricity production would reduce the finalcoal EROI value considerably ((e.g. Akai et al. 1997 in Dale, 2010 and Lund and Biswas, 2008). EROI figures do not take into accountthe high life-cycle greenhouse gas emissions from thermal elec-tricity production, and coal-fired systems in particular (Raugeiet al., 2012). This could, with difficulty, be worked into future,more comprehensive EROI calculations.
Most alternative renew-able energy sources appear, at this time, to have considerably lower EROI values than any of the non-renewable fossil fuels. Wind and photovoltaic energy are touted as having substantial environmental benefits. These benefits, however, may have lower returns and larger initial carbon footprints than originally suggested (e.g. the externalities associated with the mining of neodymium and its subsequent use in wind turbine construction).
The energy costs pertaining to intermittency and factors such as the oil, natural gas and coal employed in the creation, transportand implementation of wind turbines and PV panels may not be adequately represented in some cost-benefit analyses. On the positive side, the fact that wind and PV produce high quality electricity needs to be considered as well.
Thus society seems to be caught in a dilemma unlike anything experienced in the last few centuries. During that time most problems (such as needs for more agricultural output, worker pay, transport, pensions, schools and social services) were solved by throwing more technology investments and energy at theproblem. In many senses this approach worked, for many of these problems were resolved or at least ameliorated, although at each step populations grew so that more potential issues had to beserved.
In a general sense all of this was possible only because there was an abundance of cheap (i.e. high EROI) high quality energy, mostly oil, gas or electricity. We believe that the future islikely to be very different, for while there remains considerable nergy in the ground it is unlikely to be exploitable cheaply, oreventually at all, because of its decreasing EROI. Alternatives such as photovoltaics and wind turbines are unlikely to be nearly as cheap energetically or economically as past oil and gas when backup costs are considered.
In addition there are increasing costs everywhere pertaining to potential climate changes and other pollutants. Any transition to solar energies would require massive investments of fossil fuels. Despite many claims to the contrary—from oil and gas advocates on the one hand and solar advocates onthe other—we see no easy solution to these issues when EROI is considered.
If any resolution to these problems is possible it is probable that it would have to come at least as much from an adjustment of society's aspirations for increased material affluenceand an increase in willingness to share as from technology. Unfortunately recent political events do not leave us with greatoptimism that such changes in societal values will be forthcoming.
