Environmental Engineering Reference
In-Depth Information
1
A Survey of Long-Term Energy Resources
1.1
Introduction
All energy resources on earth have come from the sun, including the fossil fuel
deposits that power our civilization at present. Plants grew by photosynthesis starting
in the carboniferous era, about 300 million years ago, and the decay of some of these,
instead of oxidizing back into the atmosphere, occurred underground in oxygen-free
zones. These anaerobic decays did not release the carbon, but reduced some of the
oxygen, leading to the present deposits of oil, gas, and coal. These deposits are now
being depleted on a 100-year timescale, and will not be replaced. Once these
accumulated deposits are depleted, no quick replenishment is possible. The energy
usage will have to reduce to what will be available in the absence of the huge deposits.
The words sustainable and renewable apply to this vision of the future.
There is clear evidence that the amount of available oil is limited, and is distributed
only to depths of a fewmiles. The geology of oil very clearly indicates limited supplies.
It is agreed that the continental U.S. oil supplies have mostly been depleted. Deffeyes
(Deffeyes, K. (2001) Hubberts Peak (Princeton Univ. Press, Princeton) authori-
tatively and clearly explains that liquid oil was formed over geologic time in favored
locations and only in a window of depths between 7500 and 15 000 feet, roughly
1.5
-
3 miles. (At depths more than 3 miles the temperature is too high to form liquid
oil from biological residues, and natural gas forms). The limited depth and the
extremely long time needed to form oil from decaying organic matter (it only occurs
in particular anaerobic, oxygen-free locations, otherwise the carbon is released as
gaseous carbon dioxide), support the nearly obvious conclusion that the worlds
accessible oil is going to run out, certainly on a timescale of 100 years.
Furthermore, scientists increasingly agree that accelerated oxidation of the coal
and oil that remain, as implied by the present energy use trajectory of advanced and
emerging economies, is fouling the atmosphere. Increased combustion contributes
to changes in the composition of the rather slim atmosphere of the earth in a way that
will alter the energy balance and raise the temperature on the earths surface.
Dramatic loss of glaciers is widely noted, in Switzerland, in the Andes Mountains,
and in the polar icecaps, which relates to sea-level rises.
