1 The present-day perspective
Notwithstanding the rapid increase in energy consumption depicted by Figure 1, the average per capita consumption of commercial energy sources has not increased much, if at all, since 1975 (Figure 2a), even in Europe and North America.
However, the bulk of this annual consumption depletes energy sources that are non-renewable.
How can the static per capita figures for global energy consumption in Figure 2a be reconciled with the dramatic increase shown in Figure 1?
The global population increase (Figure 1) drives a corresponding increase in energy consumption despite a per capita consumption that is approximately constant.
In 2002, fossil fuels provided >75% of global primary energy consumption — a further spur for long-term planning, since these finite resources are being rapidly depleted. As Figure 2b shows, renewable energy sources contributed only 18.4% towards global consumption in 2002, and of that the greatest proportion was from traditional burning of biomass. As reserves of fossil fuels inevitably dwindle, other sources of energy must be exploited more than at present, to ensure that current levels of consumption can be sustained (or increased).
The inequalities in consumption shown in Figure 2a are further complicated by unequal distribution of fossil fuel resources (especially oil) across the globe (Figure 3). As reserves dwindle, these inequalities are likely to foster increasing political tensions. It is notable that, for many of the major conflicts of the late 20th and early 21st centuries (e.g. Iran-Iraq war, both Gulf Wars), fossil fuel supply was a critical (if understated) factor. The same inequalities of consumption and reserves may also force the development of alternative energy sources at different rates in different regions.
How long will global fossil fuel reserves last at current consumption rates? Proven reserves suggest ~190 years of coal, ~70 years of gas, and ~40 years of oil, but these figures do not take account of discoveries of new reserves, or technological advances in extraction or production. However, the rate of new petroleum discoveries is declining relentlessly, while rates of energy consumption have risen steadily from 1900 onwards, suggesting that current consumption rates are not sustainable in the long term. The underlying truth is that fossil fuels are ultimately finite resources, and at anything approaching current global consumption rates they will be depleted as rapidly as they have risen to dominance. Were non-conventional sources of petroleum, such as the huge oil sand deposits of western Canada, to become economic, that truth would still apply in the long run. As Figure 4 shows, production of conventional oil and gas is predicted to peak between 2005 and 2030, and the graphs are a stark illustration of the short lifetime of oil and gas use relative to human history.
It is clear from this brief summary of the global energy situation in the early years of the 21st century that a shift in energy strategy is inevitable on geological, economic and political grounds. And, of course, there is also a profound environmental dimension to such decision making. The extent to which each contributing consideration will govern such a shift is hard to judge. So how can we make such long-term decisions from our short-term perspective? The next section examines this dilemma, and evaluates some initial attempts at forecasting the future of energy supply.