**2.1 Expected time to depletion**

The size of fossil fuel reserves and their times to depletion are fundamental issues with conflicting answers given by experts. According to one estimate, the fossil fuel reserve

Modern Transitions in Saving Energy and the Environment 195

One popular perception about oil and gas (and coal) is that they will be suddenly depleted

Fig. 1. Popular perception about Oil and Gas, and Alternative Energy. Fallacies are that there will be (a) a mostly complete depletion of oil and gas (b) Alternative energy

energy will never come close to the energy production formerly by fossil fuel.

Fig. 2. A more realistic expectation of the decline where Oil and gas, rather than being completely depleted, will continue to decline, with rising prices, for a long time. Alternative

energy will rise to levels much lower than former levels of oil and gas.

In reality, the effect of diminishing supply and rising prices will soon cause consumption to decrease. Contrary to most existing speculations, the issue of depletion is complicated by the fact that, today it is commercially viable to extract at best about two-thirds of fuel in a reserve. There are large residual reserves of oil under the ground, which are not commercially feasible to extract today, but will become very attractive several decades later. The reality is that rather than being completely depleted, fossil fuel will go into a long decline for many decades, during which prices will continue to rise. During this time, both fossil fuel and renewable energy will exist side by side (Figure 2). However, renewable

production will be comparable to former levels of oil and gas.

**2.3 Continuous decline, rather than total depletion** 

(Figure 1).

depletion times for oil, coal and gas are approximately 35, 107 and 37 years, respectively (Shafiee, 2009). Accordingly, coal is expected to be available up to 2112, and will be the only fossil fuel remaining after 2042.

The consumption of fossil fuel in the next few decades is complicated by uncertainties about known and future reserves, and our consumption rates. Speculation over the next few decades is further complicated by the large numbers of variables and unknowns, some of which are identified below:


In spite of these uncertainties and unknowns about the future of fossil fuel, there is consensus as to the importance of conserving fuel today.
