we use a given resource like food, energy,
water, or minerals, we wonder how long that
resource will last. For renewable
resources like food or water, the resource will
last indefinitely as long as the amount that we
take does not exceed the amount that is
regenerated. For non-renewable resources
like fossil fuels or minerals extracted from the
earth, the longevity of the resource depends on
rate of discovery and depletion - keeping in mind
that resources become harder to find and remove
as they become more scarce.
For the first half of the 20th Century, most people did not think about limitations of our fossil fuel resources. That changed in the 1950s, when a geophysicist named Marion King Hubbard developed a curve that was applied to fossil fuel (particularly oil) supplies. His curve has become known as the "Hubbert Curve" and has become a controversial topic for energy experts.
The Hubbert Curve is really a basic math function. It has a bell-shape that starts at zero, rises to a peak, and then drops off to zero again (see diagram with red line below).
The rising part of the curve has three parts (phases) that resemble an "S" shape: (1) an upwardly bending "lag" phase, (2) a rapidly rising "log" phase, and (3) a plateau that levels off. Mathematicians call such an "S" shaped curve an exponential curve.
Exponential curves have widespread applicability. For example, they can be used to depict the growth pattern for an individual organism or a population. Medicinally, they can show how much oxygen is carried by the blood pigment hemoglobin as the amount of oxygen in your blood changes from low to high levels.
Unlike the exponential curve, the Hubbert curve has a parallel decreasing side that involves a rapid decline followed by tapering approach to zero (again, see diagram below).
This curve shows production in Norway. Note the good fit of the data points with Hubbert.
|This graph shows
production of oil in the United States. Note
the peak was reached in approximately 1970, though
the decline has taken longer than predicted by the
|This curve shows
daily production in non-OPEC nations. Notice
that each nation has a peak that was reached
sometime between 1970 and 2004.