Global Energy – How much Remains?
PETER NORTH calculates how long the world’s energy supplies can continue to support the existing pattern of 2% pa increase in
energy consumption. The figures suggest increasing energy consumption is unlikely to be sustainable for much longer. So,
what next for energy? One option to tackle an emerging scenario of resource shortages is to increase development of
renewable energy technologies. A concurrent approach is to conserve energy resources while we still have them. Either
way we need to get more energy conscious than we are under the existing economic system that encourages endless GDP,
population growth and associated environmental destruction.
Published in late summer 2005 issue of Pacific Ecologist - with cartoons and text highlights - available from PIRM. PO Box 12125, Wellington or pirmeditor@paradise.net.nz -
Part of a 72-page issue covering energy, food security, water crisis & pathways to sustainable societies.
A popular Saudi Arabian proverb runs: “My grandfather rode a camel, my father drove a car, I fly a jet plane, my son
will ride a camel.” According to this view from the oil capital of the world, the oil bonanza on which the world has
been having a long free lunch has to end sometime. If the proverb holds true, after the hydrocarbon era has run its
course, the future will look much like the past when much of the human race lived on the renewable energy of sunshine
and firewood, the rich got around on domestic animals and the poor walked.
Energy optimists disagree with this view of the future, claiming plenty of oil lies underground somewhere waiting to be
tapped. In any case, they point out, oil is but one energy source. In a world of boundless resources, when oil supplies
run down, we merely switch to other forms of energy. As these are used up too, prices will rise and the market will
deliver us further substitutes. And thus the present economy of endless growth that we have got to know and love can
stretch indefinitely into the future. Which of these two visions of the energy future is likely to be more accurate?
How much energy is left?
If we look at the total energy picture and consider all currently known energy sources, and perhaps speculate about a
few that are only thought about, we can ask: how much energy is left in the world? How long will it last? And once used,
can it be replaced by something else?
Energy resources fall into two broad categories: renewable and non-renewable. Ultimately the planet’s energy comes from
three sources: the sun, energy of radioactivity of Earth’s creation material, or momentum energy of objects in the solar
system. In the very long term, none of this energy is unlimited. But for the purposes of human use, incident solar
energy in its various forms such as biomass, hydro, photovoltaic cells, wave power and wind power can be considered
sources of renewable energy, as can geothermal energy from hot radioactive creation material and tidal energy from the
momentum of the Earth/Moon/Sun system. The major non-renewable energy sources are hydrocarbons – oil, natural gas and
coal – which can be regarded as stored solar energy from photosynthesis of millions of years past, and nuclear materials
such as uranium.
Currently most of the world’s energy comes from non-renewable sources. In 2001, the global energy split was as follows:
Table 1 Sources of Global Energy – 2001
Source
Percent
Oil
42
Natural Gas
23
Coal
23
Nuclear
6
Total Non-Renewable
92
Hydro
7
Other
1
Total Renewable
8
Source: US Energy Information Administration [1]
We should note here that these figures probably understate the amount of energy in the Third World coming from
traditional resources of dung and firewood.
A common unit of Energy Accounting
To complicate the picture a little, the world uses all sorts of disparate units to report its energy consumption and
production. Units tend to be traditional to particular industries. Oil is generally measured in barrels (equivalent to
42 US gallons). Natural gas is measured in cubic feet (at ambient temperature and one atmosphere).Coal is measured in
tones. Uranium is measured in tonnes of natural uranium. Energy in global quantities is mostly reported in “Quads” – a
rather odd unit defined as a quadrillion (1015) Btus (British Thermal Units).
For an exercise like this which seeks to contrast, compare and aggregate energy supply from its various sources, energy
measured in its different ways needs to be reduced to a common unit. Since the world outside the US has adopted the
metric system, I use the fundamental metric unit for energy – the Joule. For convenience the numbers are expressed in
scientific notation throughout (ten to the power of something) because many of the numbers are so large.
Table 2 Common Conversion Factors
Converted From
Converted To
Factor
Example
Energy
Btu
Joule
1,045
1 Btu = 1,045 Joules
Quad
Btu
1015
I Quad = 1015 Btus
Quad
Joule
1.045 x 1018
1 Quad = 1.045 x 1018 Joules
Oil
Gigabarrel (Gb)
Barrel
109
1 Gigabarrel = 109 Barrels
Barrel
US Gallon
42
1 Barrel = 42 USG
Coal
Gigatonne (GJ)
Tonne
109
1 Gigatonne = 109 Tonnes
Power
Joule
Watt
1 Watt = 1 Joule per second
Kilowatt-hours
Joule
3,600
1 kW-hour = 3.6 million Joules
Making an Estimate
For the purposes of making a first approximation of the total non-renewable energy endowment, let’s suppose, when one
non-renewable energy resource is in decline another can be substituted. If this is assumed, we can convert the known
reserves of energy resources into a single common energy unit and thereby approximate the total amount of useable energy
on the planet. Depending on what we assume about future demand, we can then make a first order estimate on how likely
ALL non-renewable resources are likely to last
To do this, we need to know two things: the energy content of non-renewable energy resources and the physical quantities
of the remaining resources. Neither of these can be estimated with complete accuracy. But the first is certainly easier
than the second!
Energy Content of Different Resources
The following table, drawn from various sources as noted, summarizes typical energy contents for various resources.
These figures are used in later calculations of total energy available, and the time to go to energy exhaustion. The
energy content of broad categories of resources varies, to some degree, with the quality of the deposit. For the
purposes of a first approximation, these differences will be ignored for oil and gas, but included for coal, since the
difference in energy content for different grades of coal is significant.
Table 3 Energy Content of Various Fuels
Fuel
Energy Content
Conversion Reference
Oil
5.8 x 109 Joule per barrel
Ref 3
Gas
1.07 x 106 Joule per cubic foot
Ref 5
Coal – High Grade
25 GJ per tonne
Ref 7
Coal – Low Grade
15 GJ per tonne
Ref 7
Uranium
5 x 1014 Joule per tonne of natural uranium
Ref 6
Quantities of Remaining Resources
Estimating Earth’s store of energy resources has become a fraught subject in recent times, with a wide range of
predictions from politicians, economists and geologists and the like. A key factor in assessing what might or might not
be available as a future energy source is how much various low-grade energy assets, such as shale oil, future technology
will render commercially viable. Similarly, the cut-off grade of non-renewable resources such as uranium may improve in
future years.
Then there is the question whether any “new” non-renewable energy resources are likely to come along to help out the
energy supply. Over 60-years-ago, uranium became the last major non-renewable energy resource to be exploited. But in
recent times, a case has been made for using methane hydrates found on the ocean floor as an energy resource. Technology
to extract methane from methane hydrate on the sea floor appears very difficult in theory, does not presently exist in
practice and would carry the risk of releasing massive quantities of methane, a potent greenhouse gas to the atmosphere.
In this article, no contribution to future energy has been allowed from methane hydrates. (see book review section,
Methane Hydrates, the Clathrate Gun Hypothesis)
The number of estimates of future energy supplies that can be made is the same as the number of assumptions that can be
made on the subject. Since room is restricted, this article considers two cases only. The first is based on an average
of published data from reputable sources for known existing resources (Case 1). The second includes using lower grade
resources, such as shale oil (Case 2). How long energy supplies hold out for these two cases is then calculated based on
expectations of what might happen with consumption.
Oil
Estimates of the original global endowment of recoverable reserves of conventional oil (including yet to be discovered
oilfields but excluding tar sands and shale oil) range between 2,000 Gigabarrels by people like Campbell and Deffeyes to
2,700 Gigabarrels by the US Department of Energy. Of this original endowment, so far we have used about 1,000
Gigabarrels. The World Oil Journal, estimates about 1,000 Gigabarrels (1012 barrels) of oil remains to be used. According to the Oil and Gas Journal [2] it is 1,200 Gigabarrels. According to the US Department of Energy it is 1,700 Gigabarrels. In this article, Case 1 will
use 1,000 Gb as the oil remaining. Case 2 will use 1,700Gb.
Natural Gas
The current estimate for global reserves of natural gas is around 5.5 x 1015 cubic feet. [3] This is the figure used for Case 1. While estimates of reserves include a figure for undiscovered resources,
historically these have tended to err on the low side. Trainer8 cites figures of 10,000 x 1015 cubic feet. If we were to take a figure half way between these two, to include an allowance of 50% for gas fields yet
to be discovered, the global reserves for natural gas would go to 8.25 x 1015 cubic feet. This is the figure used for Case 2.
Coal
Based on figures from the World Energy Council (that are broadly supported by a number of other authorities on the
subject) reserves of coal for Case 1 are estimated at 1,080 billions of tonnes. [4] For convenience of calculation, coal is divided into two grade categories: bituminous coals and anthracite with a
higher energy content and lignite and sub-bituminous coals with a lower energy content. Much higher reserve figures for
coal are also cited by some writers. Trainer8 quotes figures of around double that of the World Energy Council. This
estimate is taken as Case 2.
Table 4 Coal - Recoverable Reserves (billions of tonnes)
Type of Coal
Case 1
Case 2 (Same proportions of coal grades as Case 1)
Recoverable Anthracite and Bituminous
571
1055
Recoverable Lignite and Sub Bituminous
512
945
Total
1,083
2,000
Tar Sands
The world has extensive near-surface deposits of tar-sand mixtures which can be used to produce oil. The total amount of
tar sands is estimated around 300 Gb oil equivalent. Syncrude in Alberta, Canada is one company already in production on
a tar-sands-to-oil project. However exploiting the resource does have some downside from an energy viewpoint. The
process liberates tar from sand using steam, which requires considerable energy, estimated to be one third of the energy
obtained from the oil the process produces. In addition tar must be hydrogenated to produce oil. Syncrude uses “stranded
natural gas” for this purpose (ie natural gas distant from a pipeline). Exploiting tar sand deposits that don’t happen
to have a stranded natural gas deposit handy will be a lot more questionable. Case 1 allows for 25% of the energy in tar
sands being recovered. Case 2 allows 50%.
Shale Oil
The world also has extensive deposits of shale oil – estimated at 400Gb oil equivalent. The phrase “shale oil” is to a
degree a misnomer suggesting this stuff might be more useful than it’s ever likely to be. Shale oil isn’t oil at all.
It’s kerogen, which in the normal course of events only becomes oil and gas after residing for a hundred million years
or so in the hot underground rocks of Earth’s pressure cooker. No process has yet proved successful in turning shale oil
into crude oil, though many companies have tried. Case 1 considers shale oil will never be an energy source. Case 2
allows for 25% of the intrinsic energy of shale oil being someday recoverable.
Uranium
The energy content of the world’s reserves of uranium is an order of magnitude less predictable than energy from fossil
fuels. Unlike hydrocarbon deposits, where the oil, gas and coal is extracted with little associated waste matter, the
grade of uranium ores varies from high grade ores downward. The “cut-off” grade where mining uranium becomes uneconomic
in terms of money depends on the current ore price. The “cut-off” grade in terms of energy depends on the energy needed
to extract uranium from low grade ores, compared to the energy produced from the nuclear power plant.
Another complicating factor is that natural uranium exists as two isotopes. Most of the energy from nuclear power
stations of current design comes from U-235 which only occurs in uranium ore at a concentration of seven parts per
thousand. For most nuclear power station designs, the reactor fuel is “enriched” to around 3-4% U-235. After enrichment,
the balance of the non U-235 rich, “depleted” uranium is a radioactive nuisance (though depleted uranium does make
excellent bullets.)
Furthermore, it is possible to convert some U-238 into fissionable fuel in “fast breeder” reactors. However fast
breeding has proved disappointing technology. Currently the world’s entire stock of fast breeder reactors located in the
US, UK, France, Japan and Russia, have been de-commissioned. Not widely realised is that once we have used up the U-235
existing in the world’s supplies of uranium-generating conventional nuclear power, the options for technology like fast
breeders will no longer be available since fast breeders need U-235 or plutonium as start-up fuel. If we are to adopt
breeder reactions as a solution to a likely future energy crisis, we need to be doing something now. We aren’t. So it
probably isn’t going to happen.
Yet further possibilities are using thorium (which like U-235 is fissionable [5] ) and extracting uranium from seawater where it exists in such dilute quantities that the process is most unlikely to
be net energy positive (ie we are unlikely to get more energy out of the uranium we succeed in extracting than we put
into processing the sea water). Such possibilities outside the present range of power plants of current design are long
shots. While the uranium deposits of the world are being mined for energy production, it would be unwise to assume the
source of the world’s nuclear power will be fuelled by anything but U-235 energy from uranium ores of a reasonable grade
and fissioned in conventional nuclear power plants.
Taking these factors into account, the most commonly reported estimate of global deposits of uranium from ore at present
grades that are economical to extract, contain around 3 million tonnes of natural uranium (ie containing nature’s mix of
U-235 and U-238 isotopes), [6] with perhaps about the same energy content later available if lower grade ores or thorium reactors prove net energy
efficient. Three million tonnes of natural uranium equivalent is assumed for Case 1 and 6 million tonnes for Case 2.
Any allowance for fusion power is excluded. After 50 years of unsuccessful attempts to harness nuclear power through
fusing light elements such as hydrogen, helium and lithium, the technology looks unlikely to arrive in time to save us.
Total Non-Renewable Energy
Total global supplies of non-renewable primary energy calculated for both cases are summarised in the tables below:
Table 5 Total Energy Resources – Case 1
Source
Quantity (Text & Table 4)
Units
(Table 2)
Energy per Unit (Table 3
Total Energy (J)
Oil
1,000
Gb
5.8 x 109 Joule per barrel
5.8 x 1021
Gas
5.5
1015 Cubic Feet
1.07 x 106 Joule per cubic foot
5.9 x 1021
Coal – High Grade
571
Billion Tonnes
25 GJ per tonne
1.43 x 1022
Coal – Low Grade
514
Billion Tonnes
15 GJ per tonne
7.7 x 1021
Oil Tar
25% x 300
Gb
5.8 x 109 Joule per barrel
0.4 x 1021
Shale Oil
0
Gb
5.8 x 109 Joule per barrel
0
Uranium
3 x 106
Tonnes
5 x 1014 Joule per tonne of natural uranium
1.5 x 1021
Total
3.56 x 1022
Table 6 Total Energy Resources – Case 2
Source
Quantity (Text & Table 4)
Units
(Table 2)
Energy per Unit (Table 3
Total Energy (J)
Oil
1,700
Gb
5.8 x 109 Joule per barrel
9.9 x 1021
Gas
10
1015 Cubic Feet
1.07 x 106 Joule per cubic foot
1.07 x 1022
Coal – High Grade
1055
Billion Tonnes
25 GJ per tonne
2.64 x 1022
Coal – Low Grade
945
Billion Tonnes
15 GJ per tonne
1.42 x 1022
Oil Tar
50% x 300
Gb
5.8 x 109 Joule per barrel
0.9 x 1021
Shale Oil
25% x 400
Gb
5.8 x 109 Joule per barrel
0.6 x 1021
Uranium
6 x 106
Tonnes
5 x 1014 Joule per tonne of natural uranium
3.0 x 1021
Total
6.57 x 1022
The Quality of Energy
A final note to the calculation should be added. In this simplified analysis, we have assumed one source of energy can
be substituted for another. This is a reasonable first level approximation, but not totally accurate.
Oil, the resource most likely to be in short supply first, is the energy industry’s most versatile product. Of the three
phases of matter, liquids are the most convenient to transport and distribute. One of oil’s priceless advantages is that
it is a liquid under normal ambient conditions. Next best of the hydrocarbons is natural gas, chemically part of the
same series as oil. Broadly speaking, gas will do the same job as oil, but not as easily. Coal, being a solid, is not
quite as adaptable as the other hydrocarbons and has lower energy content per unit weight. Coal is most usable in power
stations and least usable in airplanes. Uranium energy is less adaptable again. Nuclear power plants for ships and
submarines can be built, but don’t expect a nuclear-powered car any time soon.
In addition, the way energy is measured is occasionally a source of confusion. Most measures are expressed as “primary”
energy, as the energy released as heat, that can be recovered from the fuel. But under the laws of thermodynamics, only
a fraction of this heat can be converted into useful work. Though high-efficiency fuel cells are theoretically
practicable, after at least 50 years research, none are yet in large-scale commercial production. Presently most energy
sources, if converted to electricity, go through a heat engine of some sort which is likely to be about 35% efficient.
At best it takes about 3 kW of primary energy to produce one kW of electricity. Since some fuels produce more usable
energy per unit of intrinsic energy than others, energy content isn’t strictly interchangeable between one fuel and the
next. And since, in our market-driven consumption-based economy, we are cherry-picking the highest quality fuels first -
in particular oil - the first approximate analysis outlined in this article is likely to err on the optimistic side.
How Long might supplies hold out?
Given the present culture of global economic management, it’s almost impossible to make sensible predictions on how long
supplies of non-renewable energy will last even if we can get confident about how much energy we have. Two reputable
institutions forecasting aspects of mankind’s future for the next century or so are MIT, which published “Limits to
Growth, The 30-year update” in 2004, [7] and the “Intergovernmental Panel for Climate Change” (IPCC) which publishes annual updates on its projections for
future climate. “Limits for Growth” considered ten “scenarios” for the future. IPCC considered 40 (which it termed
“storylines”). [8] Both these bodies produced such a wide range of answers depending on the assumptions they barely qualify as predictions
– just possibilities for the future. Both found the most important factor in determining the prospects for aspects of
the natural world, in particular climate and resources, was not so much what nature provided but how mankind manages its
future in the coming decades.
Currently, society is incredibly wasteful of energy. Using “growth” as the principal measure of progress in the consumer
economy is the single most important factor driving mankind into fast exhaustion of its energy resources. Reporting
economic performance as increases in GDP - a unit that measures waste as “progress” – merely proves an adage well known
to management consultants - poor reporting standards yield poor decision-making. Comments of most economists on the oil
price spike in 2004 were typical. In expressing concern about the tightening oil market, most economists worried not how
the global growth rate (of 5% or so) might reduce the oil supply, but how the oil shortage might reduce the growth rate!
The most obvious conservation measures could stretch energy supplies considerably. Existing technology such as
energy-saving light globes and hybrid cars, save money and greatly improve energy efficiency with no loss of amenity.
But passion for growth reigns supreme among policy makers and two percent annual growth of energy consumption continues,
to the delight of coal-mining companies, bulk-shipping companies and primary- producing countries - to mention a few of
the short-term beneficiaries of mankind’s profligacy. It would be unwise to expect a rational strategy for dealing with
energy shortages will emerge any time soon.
Since a culture of energy conservation is proving so difficult to implement, a first measure approximation of long-term
energy supply and demand is to examine the consequences if present patterns of energy use remain as they are. World
total energy consumption in 2001 was 404 Quads (=4.22 x 1020 Joules). Assuming non-renewables continue to supply 92% of total energy, and the rate of consumption continues to rise
at 2% pa, simple arithmetic shows the non-renewable energy endowment calculated for Case 1 would last until 2054, and
for Case 2 until 2076.
Neither of these two calculations, it must be emphasised, is a prediction. What the calculation shows is that the growth
model of increasing energy consumption at 2% per year – is impossible under the stated assumptions about energy
resources. Only if an abundant new energy source is found can the world keep raising its energy consumption at an
exponential rate over a long period. Plenty of depletion curves for natural resources have been observed historically.
Depletion of a stressed resource follows a curve, the general shape of which, if not the precise detail, is well
established. As its consumption rises, the supply of a resource reaches a peak then declines over a number or years, or
even centuries. After peak production, one way and another, societies whether animal or human, are forced to adjust to
diminishing resources - which is almost always an arduous experience.
Renewable Energy
By definition, non-renewable resources are not sustainable in the long-term. Unless sufficient renewable resources are
found in time to make up for the shortfall in non-renewable energy, energy consumption will commence a decline and
thereby alter the way we live. So a key question about the energy future is, what are the prospects for renewable
energy? One of the assumptions of the foregoing section was that non-renewable energy resources would continue to play a
minor role (currently shown in Table 1 as 8%) in energy production. Can this assumption be relaxed? Can the contribution
of renewable energy to total energy supplies be increased?
This subject is too big to tackle here. However two general points can be made about renewable energy, the first being
that it takes energy to bring it on-stream. So it would be smart, while we still have it, to invest the remaining
hydrocarbon energy in renewable energy projects instead of burning it up on budget holidays in Bali and driving cars
around in aimless circles. Secondly, renewable energy projects on a large scale are likely to need a long lead time to
develop. So it would be smart to start getting serious about renewable energy sooner rather than later.
The few books that have been written specifically on renewable energy options are generally not optimistic. Ted Trainer, [9] who has worked for a number of years quantifying various renewable energy options, concludes that no future society
running on renewable energy can supply energy on the scale it has been consumed during the hydrocarbon era. However, Ted
points out that living on an energy-frugal budget and living a full life are not incompatible. Heinberg’s follow up book
“Power Down” also examines the prospect for an energy-depleted world. The bleakest view of the energy and resource
deficient future is summed up by gloomy prophets such as Jay Hanson in the self-explanatory term, “die off.” [10]
The foregoing is the view of the pessimists. But what of the optimists? The major argument advanced by most economists,
is that market forces will inspire inventors to introduce clever new energy-producing technologies when energy prices
rise sufficiently to prompt them to do so. These unknown technologies, which of course cannot be revealed at this stage
(since they haven’t been invented yet), will enable the growth economy to endure indefinitely. On this assumption
economics bases its energy plans for the near and distant future.
How realistic are these expectations? Considering that no new major energy-producing technologies have been developed
for a long time, the economic argument sounds suspiciously like the cargo cult economics after the Second World War when
some Melanesians thought if they stared at the empty sky long enough, food-bearing planes would arrive as they had in
the past. Despite a sustained program of sky-gazing, the planes failed to materialize. Pessimists my well ask if the
market-inspired future energy model would fare any better?
In Conclusion
Given its vital importance, interest in the planet’s longer-term energy future has been muted. Most energy discussions
so far have been about the oil price, and the likely timing of peak-oil production. (Like the peak of the stock market,
no one will recognize the oil peak until it’s already history).
No known technology is yet capable of transforming the global economy from one which relies on 92% of non- renewable
resources into being 100% self-sufficient with renewable energy. But eventually, the choice is to develop some renewable
energy resources or suffer the consequences of increasing energy shortages. Since the lead times on new technology and
construction of infrastructure are likely to be considerable, the sooner we get serious about developing and building a
sustainable economy the more likely it is to happen. Every day we fritter away denying the problem exists is a day the
window of opportunity to implement sustainable alternatives closes a little further.
The 2004 oil price spike may have been a wake-up call to some. But with the global economy ripping along at 5% growth,
and with China and India trying to turn themselves into energy-consuming economies, it seems unlikely this call will be
heeded. We still live in the era of the unplanned market economy in which central planning is anathema, resources are
considered infinite and the future is left to unfold according to its own pattern. Do we need to throw-out the growth
economic paradigm before it’s too late and develop new economic theories to deal with the emerging scenario of resource
shortages, environmental destruction and over-population?
*************
FOOTNOTES:
1. Energy Depletion\ConocoPhillips — Global Energy.htm
2. See US Department of Energy compilation of statistics from various sources at http://www.eia.doe.gov/pub/international/iea2002/table81.xls
3. See US Department of Energy http://www.eia.doe.gov/emeu/international/reserves.html. and http://www.eia.doe.gov/pub/international/iea2002/table81.xls
4. World Energy Council, Table 8.2, “World Estimated Recoverable Coal”
5. For a summary of the possibilities of thorium reactors, see World Nuclear Association’s “Nuclear Electricity” on http://www.world-nuclear.org/education/ne/ne3.htm
6. See “Uranium Ore Deposits” http://www.antenna.nl/wise/uranium/uod.html and Energy Conversions: Typical Heat Values of Various Fuels http://patzek.berkeley.edu/E11/energyconversionfactors.htm
7. Meadows D, Randers J, Meadows D “Limits to Growth – The 30-Year Update”, Chelsea Green Publishing Company, White
River Junction, Vermont, 2004.
8. IPCC Climate Change Report: http://www.grida.no/climate/ipcc_tar/wg1/index.htm
9. Ted Trainer “Renewable Energy; What are the Limits?” http://www.arts.unsw.edu.au/tsw/D74.RENEWABLE-ENERGY.html
10. Jay Hanson, who some years ago abandoned hope that the energy problem can be solved, is known by some as the Paul
Revere of hydrocarbon depletion. See Jay Hanson’s website at http://groups.yahoo.com/group/dieoff/message/10. For reading only by those of robust mental disposition.
*************
Peter North, is an engineer, with qualifications in economics and accountancy. He has worked in the mining industry and
later in the manufacturing industry. In recent years he has combined teaching finance and accounting with writing books,
articles and papers combining technological, economic, environmental and political themes. Eight of Peter’s books have
been published, with an additional book, “Culture Shock! Cambodia” to be published in 2005. This article is copyright of
the author and Pacific Ecologist. Reproduction of articles in Pacific Ecologist, may be allowed on request to the author
and Pacific Ecologist, provided credit is given to Pacific Ecologist as publisher’s of the original article.