"Population growth and energy demand are exhausting the world's fossil energy supplies, some on the time scale of a single human lifespan."...  ...Paul B. Weisz.

Commentary of the Day - July 26, 2004:  Environmental Education.

The July 2004 edition of Physics Today (the "trade" magazine for the physics community) included two articles that deserve a much wider audience than they are likely to receive in such a specialized journal.  The first by Paul B. Weisz, emeritus professor of chemical and bioengineering at the University of Pennsylvania, addresses the constraints on the world's long-term energy supplies.  The second by Albert A. Bartlett, emeritus professor of physics at the University of Colorado at Boulder, looks at the pressure that an exponentially growing world population puts on limited supplies of energy.

Discussions of world energy usage usually are couched in terms of "quads".  One quad (Q) is equal to 10¹⁵ BTU (British Thermal Units).  To get things into perspective, the current US energy consumption is about 100 Q/year, and that is approximately one quarter of the world's total energy consumption.  The central problem is that energy resources are limited while the demand for energy, driven mostly by an increasing population (both in the US and world wide), is increasing exponentially.  Here in the US energy demand is growing at about 1.5% per year, while world wide the demand is estimated to be growing at somewhere between 1% and 2% per year owing both to population growth and industrial development.

The growth in world population in the last two centuries -- which coincides with the introduction of fossil fuels -- has been truly startling, as can be seen in Fig. 1.
 

Fig. 1: World population growth.  (From Physics Today, July, 2004, p. 48)

As Weisz outlines in his article, fossil and conventional nuclear fuel resources really are quite limited.  Petroleum production in the US peaked in 1970, and has been on the decline ever since.  The estimates for world-wide petroleum reserves vary, but given the most optimistic scenario (twice the current proven reserves) these will be exhausted in less than 100 years if population growth continues at about 1% per year.  A natural gas shortage has developed in the US in recent years (demand has been growing at about 2.8% per year).  Proven world-wide natural gas reserves (5,500 Q) will be exhausted in under 40 years if demand continues to grow at 2.8% per year.  Estimated world-wide natural gas reserves amount to about 10,400 Q.  With some conservation (2% growth in demand instead of 2.8%), these reserves will last about 65 years.

In addition to conventional petroleum and natural gas resources, a fair amount of fossil fuel reserves exist in the more dilute form of oil shale.  However, recovering usable fuel from these reserves will be expensive; and, will release far more CO₂ into the atmosphere than is the case with current fossil fuels.

The United States has relatively large proven reserves of coal (about 5,700 Q).  If usage were to continue at the current rate (no growth in demand), these reserves would last for more than 250 years.  However, if usage grows at the same rate as population growth (1.1%), the reserve would be exhausted in about 125 years.  If usage patterns change -- for example, if coal is converted into liquid fuel to replace petroleum -- then the US coal reserve would last for about 80 years with a 1.1% demand growth rate.  The US reserves of conventional nuclear fuels (fissionable material) are fairly large, and at present only about 8% of our total energy demand is met by nuclear sources.  However, if we were to increase our use of conventional nuclear sources to the same level as our coal usage, US reserves would be exhausted in under 60 years.

As Bartlett points out in his article, we already have passed the peak in world daily production of petroleum per capita!  Even though more oil is being pumped, the demand from population growth is outstripping the growth in supply (see Fig. 2).

Fig. 2: World daily oil production per person.  (From Physics Today, July 2004, p. 54)

Alternative energy sources, including so-called "renewable" energy sources, are less polluting and contribute less to the global warming problem.  However, they do not solve the demand problem created by exponential population growth.  The major problem is that alternative sources such as solar, wind, and biomass are dilute energy sources that ultimately depend on the rate at which solar energy impinges on the surface of the earth.  At present, the most efficient way to harvest solar energy is to use solar cells.  These cells are roughly 20% efficient in converting solar energy to electrical energy, and they require a fairly large investment of energy to produce them.  Typical solar cells have a lifetime of 20-25 years.  They recover the energy required to make them in three to seven years.

As Weisz points out, the area required to replace conventional energy sources with solar is substantial.  For example, the US would need to cover approximately 2.7% of its land area with solar cells to produce enough energy to meet current demands.  For more densely populated developed countries, the figures are not so promising.  For example Japan would need to cover 15% of its land mass with solar cells to produce enough energy to replace its other sources.  However, some countries such as Australia and Russia would need to cover less than 0.5% of their land areas to produce their current energy demands.

Although a return to nuclear energy production often has been touted as a solution both to pending energy shortage problems and to the global warming problem, existing proven "conventional" nuclear resources would last for only a few decades if fully exploited.  Breeder reactor technology might extend these resources for a few hundred years, and controlled nuclear fusion technology might provide relatively clean energy for much longer.  Controlled nuclear fusion technology has been pursued for decades, but usable results so far have been beyond our grasp.

Unfortunately, few are willing to confront the 800-pound gorilla of energy policy; namely, the extent to which population growth affects energy demand.  For example, in recent years a substantial effort has been made to use energy more efficiently; and, indeed industry has made great strides in this area.  However, even relatively substantial improvements in efficiency are wiped out quickly by population increases.  A 20% improvement in efficiency is overtaken by population growth in just two decades.

While the technology to produce unlimited supplies of clean energy may be outside our grasp, we already know how to control population growth provided we have the political will to do so.  Economists often argue against population control, because they feel that population growth is needed for economic expansion.  However, economic growth also can be achieved by improving standards of living.

Let's start to include discussions of the effects of population growth in our environmental classes.