If a third runway is added to Hong Kong International Airport, it would not be fully operational until the 2020s. The Airport Authority argues that it is necessary, based on projections of rising demand for air travel.
But an important consideration is missing in most of the debates: the probability that so-called 'peak oil' (the peak and subsequent decline in worldwide oil production) will occur during the next two decades.
'Peak oil' analysis is based on a comparison between major discoveries of oilfields in the past, production from those fields, and the decline in major discoveries in recent decades. Many existing fields have already gone into decline, and a number of countries have seen a drop in domestic oil production for this reason.
The timing of the global peak of oil production is hard to predict. But a number of analysts have concluded that it is imminent. For example, a report prepared for the US government in 2005 by Robert Hirsch and others estimated that peak oil would occur 'within 20 years' (that is, by 2025 or earlier), and that this would cause 'protracted economic hardship', including a 'severe liquid fuels problem' for the transport sector.
Some plants of the genus Jatropha can be grown on marginal land and processed into jet fuel, and research continues on algae as a fuel source, but there is a serious problem scaling up production to supply the 60 billion to 70 billion gallons of jet fuel consumed annually by the world's airlines. Biofuels will evidently not be able to replace oil as the main fuel source for aviation.
There is uncertainty in predictions about 'peak oil', and the impacts will be complicated, because big increases in oil prices lead to recessions, temporarily reducing demand for oil. But one certainty is that the price of oil will be higher in the future because its depletion is irreversible.