The human ecology of climate change - Climate Change: Biological and Human Aspects - page 389

caveat about reserves allowance is an important one. For whereas there is plenty of
economically recoverable coal worldwide, over two centuries' worth at current rates
of production, there is less oil and gas. BP Economics Unit (2011) estimated that
there were enough commercially available proven reserves of gas to last nearly six
decades at 2010 levels of production, and only enough oil for very roughly around
four and a half decades. It needs to be remembered that the pressures for global
consumption of these resources to increase are plainly evident, as discussed earlier
in this chapter.
Of course, should prices change (as they will), today's economically recoverable
reserves may not be so tomorrow. Indeed, with increasing scarcity prices will rise, so
enabling reserves that are currently either harder to reach, or more expensive to refine
(such as sulphur-rich deposits), to be economically recovered. Then again, future
innovation and new technology may enable reserves that were previously uneco-
nomical to recover to become economical. Furthermore, as prices rise so non-fossil
technologies, formerly considered too expensive, will become economically viable.
Finally, proven reserves are a subset of total reserves, which includes deposits yet to be
discovered as well as exotic sources (possibly such as marine methane hydrates) that
are not usually considered. In short, estimates as to ultimate economically recoverable
reserves vary.
To see how these reserve caveats work, consider the analogous question of how long
US food stocks may last. One might say that adding up all the food in people's homes,
shops and warehouses, and dividing it by the rate of consumption, might give a figure
of, say, x months. However, in addition to this there will be crops growing in the fields
not yet harvested. There will also be the food wasted due to, say, combine harvesters
missing some of the crop, mishandling or poor storage. Then there are species of
food plant outside of the economic system, from apple trees in people's gardens to
raspberries growing in the wild. There are also exotic food species, that is to say
perfectly edible plants and animals that do not normally feature in most Americans'
cuisine. Finally, there will be species not normally edible that will require some sort
of processing before they can be used. In short, what can be considered the total US
food stock depends on what exactly is being considered. So, such an estimate, when
expressed in terms of a reserve/production ( r / p ) ratio, is therefore not as exact a figure
as one might think. Food in the USA will not run out on the last day of the x th month.
Quantifying oil reserves is fraught with analogous difficulties and so estimates have
to be viewed with extreme caution.
An example of how reserve assessments can be misleading comes from the Kern
River oil field. It was originally discovered in California in 1899. Calculations in
1942 suggested that 54 million barrels of economically extractable oil remained.
However, in subsequent years some 736 million barrels were recovered and a new
estimate later in the century suggested that 970 million barrels remained. What had
happened was not that the oil field had changed but that knowledge and technical
ability had increased (Maugeri, 2004). Having said this, it does not mean that oil is
an inexhaustible resource but this example does demonstrate that estimates have their
limitations.
From this it can be seen that r / p ratios are at best only a broad indication of
future potential. However, with regard to fossil fuels, they do suggest a magnitude of
resources for continued, if not increasing, exploitation throughout the 21st century