Edition 2, April 2008
Bruce Sundquist

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Reference citation format, e.g. (98C2), cites a document published in 1998 by a lead author whose last name begins with "C". The final integer (2 in this example) is a running index.

~ Table of Contents ~
[1] ~
Co-Opted Primary Productivity of Open Oceans
[2] ~ Co-Opted Primary Productivity of Remaining Aquatic Systems
[3] ~
Co-Opted NPP of Natural (Semi-Arid) Grazing Lands
[4] ~
Co-Opted NPP of Tropical Forests
[5] ~
Co-Opted NPP of Temperate Forests
[6] ~
Summary of Globally Co-opted NPP
[7] ~
Accessibility Correction
NOTE: The subject matter of Sections [8] through [12] is covered in greater detail in Reference (08S1) on this website.
[8] ~
Could Genetic Advancements Increase the Earth's Net Primary Production?
[9] ~
Could Expanding the Cropland Area Devoted to Genetically Modified Plants Produce a de facto Enhancement in the Earth's Net Primary Productivity?
[10] ~
Could Increased Consumption of Pesticides Produce a de facto Increase in Net Primary Productivity of the Earth's Croplands?
[11] ~
Could Increased Consumption of Chemical Fertilizers Produce a de facto Increase in Net Primary Productivity of the Earth's Croplands?
[12] ~
Could some Yet-to-be Discovered Procedure Produce a de facto Increase in Net Primary Productivity of the Earth's Croplands?
References ~
Table (1) ~
Summary Comparison of Co-opted Net Primary Productivities

Net Primary Production (NPP) analyses have a narrower scope than "footprint" analyses. They start with known rates of photosynthesis (the bottom of the food chain that is the source of all food and natural fiber consumed by Man). NPP analyses then compute what fraction of terrestrial NPP is consumed directly, co-opted or forgone because of human activity. The word "Net" means that the respiration of primary producers - mostly plants - is subtracted from the total amount of energy (mostly solar) that is fixed biologically to compute NPP. The most comprehensive, global-scale analysis of this type was done by Vitousek et al (86V1), although there have been some improvements to the original document by other authors as noted below. They compute that nearly 40% of the world's potential NPP is used directly, co-opted or foregone because of human activity, including 2% of aquatic primary production. Correcting for population growth since 1986 would give an updated global fraction of about 48%. A later (1995) study by the International Center for Living Aquatic Resources Management estimated that humans co-opt 8% of aquatic primary productivity -- 2% of open ocean primary productivity and 25-34% of other aquatic systems (98M1). NPP decreases over time as a result of such processes as desertification, and conversion of natural systems to croplands, pastures and areas of human habitation, commerce and infrastructure. Also, some NPP is so diffuse (e.g. tundra, alpine meadows and much open ocean) as to be effectively inaccessible to human co-option because of the extremely high costs involved in harvesting it.

The implication of all this is that the earth's human carrying capacity is limited to that that would result in the fraction of NPP co-opted becoming 100% (Vitousek et al's "intermediate" estimate). This assumes unlimited supplies of fossil fuels, water, waste-disposal sites, etc. so a carrying capacity computed on the basis of 100% NPP co-opted by humans would be optimistic. The implication of a 48% current rate of human co-option of NPP is that human populations could roughly double. This seems inconsistent with the more comprehensive "footprint" analyses that imply that humans already consume more than 100% of the productivities of the world's photosynthesis-based systems (02W1). This inconsistency can be explained by some gross inconsistencies between some of the parameters used in Vitousek et al's "intermediate" analysis and some well-established understandings of conditions in some of the Earth's key natural producers of food and fiber. There is also an important error. These inconsistencies and the error are corrected below. These eliminate most of the inconsistency between NPP co-option analyses and "footprint" analyses.

[1] ~ Co-Opted Primary Productivity of Open Oceans ~
About 75% of aquatic NPP occurs in open oceans (95P1). But there, NPP per unit area is only a third to a tenth of that in upwellings, coastal shelves, coastal (estuary) and reef systems where the overwhelming bulk of wild fish harvests occur (95P1). This diffuseness translates into fishers' fuel, labor and capital costs being 3-10 times larger per ton of catch. This explains why humans co-opt 24-35% of primary production in fresh water, upwellings, shelves, coastal and reef systems, but only 2% in open ocean systems (95P1). In essence, the diffuseness of resources in open ocean systems makes fish capture there financially prohibitive for all but a few high-trophic-level species that are being rapidly depleted. Rising fuel costs for fishing boats can only serve to make these harvesting costs even more prohibitive. The NPP of open oceans should thus be taken to be largely inaccessible to human co-option by virtue of its diffuseness. Then the co-option problem addressed by Vitousek et al should be redefined as the percentage of accessible NPP that is co-opted by Man. This diffuseness problem is unlikely to diminish over time. As prices of products from the open ocean increase, so does the price of fossil fuel for the boats that do the harvesting. The land categories Deserts, Arctic-Alpine tundra, and Chaparral also have net primary productivities that are too diffuse to be accessible to human co-option. These issues are taken up later in this document.

[2] ~ Co-Opted Primary Productivity of Remaining Aquatic Systems ~
By neglecting open-ocean systems, the fraction of accessible aquatic NPP co-opted by humans varies from 24 to 35% depending on the system (95P1). This would imply that humans could, in theory, increase their aquatic harvests by a factor of 3-4. A huge body of evidence disputes this, and shows that wild aquatic systems are, even now, being exploited beyond their carrying capacity. Below is a listing of a small fraction of this evidence. A far larger analysis of the sustainability of global systems for producing food, natural fiber and fresh water is available in Ref. (08S1) that can be found on this website. One of the six chapters is devoted to marine fisheries issues.

The error made by estimators of aquatic NPP is fairly clear. Their NPP analysis had to make estimates of (1) the average trophic level of wild marine fish being caught and (2) the ratio of the total biomass of fish in each trophic level to the biomass in adjacent trophic levels. Small errors in either estimate (within the uncertainty of the estimates) could readily increase the computed fraction of aquatic primary productivity co-opted by humans from the clearly erroneous 24-35% to something on the order of 100%, a value consistent with a huge body of data and the overwhelming consensus of those familiar with fisheries issues (07S5).

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[3] ~ Co-Opted NPP of Natural (Semi-Arid) Grazing Lands ~
Vitousek et al estimated that humans co-opt, by grazing livestock, 0.8 of the available 41.3 Gt.(gigatonnes)/ year (dry organic matter) of NPP on natural (typically semi-arid) grazing lands. This would imply that livestock grazing on natural grasslands could be expanded by a factor of 41.3/0.8 = 52 times. This is grossly at odds with a huge body of data and expert opinion that indicate that such grasslands are heavily overgrazed virtually everywhere on Earth, and that there are few untapped reserves (07S3). (Also see Ref. (08S1).) Closer examination of the Vitousek et al analysis finds an error in that analysis that explains the discrepancy between calculation and observation.

On "derived" (typically semi-humid) pastures, grazing livestock are computed to consume, directly, only 7.6% of NPP, while 100% of NPP is co-opted. On natural grazing lands these percentages are erroneously taken as 100% and 1.9%. NPP per unit area on derived pastures is taken to be the same as that on natural grazing lands. Yet grazing capacities on semi-arid grazing lands (0.1 animal-unit/ha.) are typically 20% of those on semi-humid grazing lands (0.5 animal-unit/ha.) (07S3). This indicates that semi-arid grass productivity is about 20% of semi-humid grass productivity. This means that only 7.6%x0.2 = 1.5% of co-opted NPP on natural grazing lands is actually consumed by grazing livestock. The smaller fraction probably resulting from a larger fraction of woody shrubs on natural grazing lands. Thus the amount of co-opted NPP on natural pastures should have been computed as 0.8/0.015 = 53 Gt./ year out of the available 41.3 Gt./ year. This indicated that essentially 100% of NPP on natural grazing lands is co-opted by grazing livestock - just what Vitousek et al found for "derived" pastures, and just what the overwhelming bulk of the research indicates.

[4] ~ Co-Opted NPP of Tropical Forests ~
Vitousek et al computed a global human consumption of NPP as wood to be 2.2 Gt./year. They also computed that another 1.3 Gt./ year of wood was killed as part of timber- and firewood harvesting and left on the forest floor (e.g. branches, roots, twigs). This gives a NPP co-option of 3.5 Gt./ year as a result of timber- and firewood harvesting out of a total global forest NPP of 48.7 Gt./ year of dry organic matter. Shifting cultivation, land clearing and forest plantation productivity add another 10.1 Gt./ year for a total co-opted NPP of 13.6 Gt./ year. The assumptions used to compute the ratio of co-option to consumption appears to be quite reasonable for temperate forests where about a third (16.2 Gt./ year) of global forest NPP occurs (78W1). However it is clearly much too low for tropical forests. Also the implication here is that human co-option of global forest NPP could potentially increase by a factor of about 3.5 before hitting its limit. This is clearly much too high. Below are some facts and figures that the NPP analysis by Vitousek et al must be reconciled with.

Clearly the ratio of co-option to direct consumption for wood harvests in tropical forests assumed by Vitousek et al (1.6) is too small. Also the ratio of co-option to NPP is too small, and ought to be closer to 1.0. A co-option/direct-consumption ratio of about 15.2 (justified by the data above) would give a co-option of 100% of tropical forest NPP (also readily justified by the data above). Harvests beyond sustained yield in most tropical nations would suggest that co-option should be taken as well in excess of 100% of NPP. Also much wood harvesting in tropical nations is illegal (up to 80% of total harvests (98A1) (98A2)) and/or non-commercial, and hence is not counted in harvest tallies. On the other hand, in some areas of the Amazon and the Congo, significant areas of untapped forests remain, suggesting a co-option of effectively 0% in these areas. The net effect of these four factors seems unlikely to reduce overall co-option below 100% of NPP.

[5] ~ Co-Opted NPP of Temperate Forests ~
Subtracting the above tropical forest data from Vitousek et al's analysis of forests globally would suggest that human co-option of temperate forests is about 1.17 Gt./ year of dry organic matter out 16.2 Gt./ year of NPP. This would suggest that wood co-opted from the world's temperate forests could be increased by a factor of 13.8. This, too, is grossly at odds with experience and estimates of sustainable harvests. Hagler's 1995 estimate of the sustainable long-term harvest of fuelwood and industrial fibers from the world's available forests was 3.7 billion m3 (96N1). Around 1990 over 3.4 billion m3 of wood were extracted from the world's forests and woodlots annually (91P1). Growth in wood consumption is well in excess of 1%/ year, so the surplus wood-producing capacity of the world's forests has, at best, vanished. Surpluses in some nations, are counterbalanced by harvests beyond sustained yield elsewhere. So human co-option of temperate forest NPP should, like tropical forest NPP, be taken as about 100%.

[6] ~ Summary of Globally Co-opted NPP ~
It is of interest to re-tabulate the Vitousek et al intermediate analysis of globally co-opted NPP (86V1). This is done in Table (1) below.

Table (1) brings the NPP analyses into consistency with the broader "footprint" analyses. Both basically lead to the conclusion that, under present resource management practices, no significant options exist for human numbers to grow without corresponding reductions in living standards or changes in resource management.

Table (1) ~ Summary Comparison of Co-opted Net Primary Productivities (NPPs) Computed here and those Computed in the Analysis by Vitousek et al (86V1) ~

Type of Surface Cover


106 km2



et al

As Corrected






Semi-Arid Lands (#4)















Cultivated Land





Human Areas





Other Terrestrial (#2)






#5) 92

#3) 23.1








TOTALS (percent)

#6) 47




#1 Gt. dry organic matter per year
#2 chaparral, bogs, swamps, peatlands and marshes
#3 92.4 (total) minus the 75% in open oceans that is too diffuse to be accessible.
#4 Naturally open woodlands, natural grasslands, and savanna
#5 Lakes and streams (2) + 25% of marine (90)
#6 Percent of the Earth's total surface area (510)

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It has been estimated that, today, 83% of the world's ice-free lands are impacted, directly or indirectly, by humans (02S1). The area of ice-free land in the world is about 131 million km2. 83% of 131 is 109 million km2. Of this 109 mllion km2, about 4.75 million km2 were urban lands in 2000 (Table FG.5 of Ref.(00W1)). So this suggests an area impacted by humans in terms of croplands, grazing lands and forests of about 104 million km2. But other analyses give only 85-90 million km2 as being reasonably biologically productive. (See Part (2-D-e) of Chapter 2 of Ref. (07S1).) So this is saying that human impacts, directly or indirectly, extend over all the world's reasonably biologically productive land. The percentage of the Earth's NPP co-opted by Man that is computed above seems compatible with the above analysis by Sanderson et al (02S1).

[7] - Accessibility Correction
Land categories Deserts, Arctic-Alpine and Chaparral have productivities that are too diffuse to be accessible to human consumption. Thus the NPP of these land categories (59 million km2, with a total of about 10 Gt./ year of NPP) should be treated like open ocean was treated here, and should be assumed to have a total accessible NPP of zero. The fraction of the Earth's accessible NPP co-opted by humans then becomes 96.2%. (The remaining 3.8% is in bogs, swamps, peatlands and marshes, and these serve vital rolls in terms of water supplies and flood control (08S1) so they should not be considered to be potentially useful for purposes that would degrade their current purposes. In essence they have already been co-opted by humans.)

[8] - Could Genetic Advancements Increase the Earth's Net Primary Production?
Plant breeders have never been able to fundamentally alter the basic process of photosynthesis itself, i.e. to produce more plant mass without added water, fertilizer, etc. (97B2). Instead, the "Green Revolution" contributed to food production by increasing the "Harvest Index," the fraction of plant photosynthate devoted to seed development (i.e. grain - roughly 80% of the food people eat). This Index for originally domesticated wheats was around 20%. The "Green Revolution" increased the Harvest Index for wheat, rice and corn to over 50%. Scientists see a physiological upper limit to this Index of around 60% (97B2) (93E1) or less (99M1). This suggests that further major improvements to global food supplies via genetic improvements are unlikely. This belief is supported by the fact that after 20 years of research, bio-technologists have not produced a single high-yield variety of wheat, rice or corn (97B2). Maximum rice yields have been the same for 30 years. Still, official projections from the World Bank, FAO, and IFPRI assume agricultural researchers can repeat the Green Revolution (99M1). This would require a Harvest Index of over 100% -- far beyond the theoretical limit.

Genetic improvements also have negative side effects that are likely to decrease the likelihood of future genetic improvements. The number of varieties of food grains in common use is shrinking, increasing vulnerability to pests. Also, farmers are now planting huge monocultures instead of strip-cropping and crop rotation. This gives pests an ever-increasing advantage. Since 1900, 75% of the genetic diversity of domestic agricultural crops has been lost (98H1). Without constant infusions of new genes, geneticists cannot continue to improve crops. Cultivars need to be reinvigorated about every decade in order to protect them against pests that keep adapting to the changing genetic make-up of crops. The most effective way to do this is to interbreed domestic varieties with wild ones (98H1).

The "genetically modified" crops one hears about currently are almost entirely developments to increase pest resistance. These "modifications" were developed to counteract the genetic adaptations of pests to better resist the "pest-resistant" plant species developed a decade or so earlier. So all that present-day "genetically modified" plants do is to keep one step ahead of "genetically modified" pests. Losses to pests have not decreased for some decades, suggesting that expecting significant improvements in productivity from "genetically modified" plants is likely to produce nothing but disappointment. The name of the game is now "March in Place," and there is no reason to believe this will ever change. (See [A-10])

[9] - Could Expanding the Cropland Area devoted to Genetically Modified Plants Produce a de facto Enhancement in the Earth's Net Primary Productivity?
Some undeveloped potential for genetic improvements to increase the Earth's Net Primary Production lies in the fact that not all grain crops grown in developing nations are genetically improved. Across all developing countries, modern rice varieties were being grown on 74% of the planted area in 1991, modern wheat on 74% in 1994, and modern maize on 60% in 1992 (98M2). Today's numbers would be expected to be significantly higher. However, most high-yield seed varieties of wheat, corn and rice developed by Borlaug et al during the "Green Revolution" are inapplicable for large areas of the developing world because of adverse soil conditions such as build-up of salts, iron- or aluminum excesses, or high acidity (82B1). The spread of the Green Revolution is limited to high base-status soil areas of tropical Asia and Tropical America. High base-status soils (18% of tropical soils) are already intensively exploited (75S1). It would seem therefore, that high-yielding, fertilizer-responsive crop varieties are planted on nearly all suitable lands.

Also note that the basic concept behind the "Green Revolution" is to make plants better able to utilize chemical fertilizers and organic fertilizers. In Africa, very little chemical fertilizer or organic fertilizer is used, so the Green Revolution is barely applicable to Africa. The reason why chemical fertilizers are so little used in Africa is because they cost 60 times more than they cost in the European Union (in units of hours of labor per tonne of chemical fertilizer). This is due mainly to the fact that Africa has a very poor transportation infrastructure. This, in turn, is due to Africa's high population growth rates, placing huge financial demands on the infrastructure growth needed to accommodate that population growth. In a region where the median earning is less that $2/ person/ day, this makes financial capital extremely scarce, thus Africa's bad road system (in terms of both miles of roads and quality of roads.) The reason why so little organic fertilizer is used on Africa's croplands is that the manure from livestock must be used as fuel for cooking food, since petroleum is such an expensive luxury. The result of all this is that Africa's farmers are "mining" the nutrients from their cropland soils. This is certain to diminish the net primary productivity of Africa's croplands over time. So if any small increases do occur in the extent of utilization of genetically improved crops, these increases are more than likely to be counteracted by the increasing poverty of Africa's soils - soils that were of very low quality even long before Man set foot in Africa. (See Chapter 1 of Ref. (08S1).)

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[10] - Could Increased use of Pesticides Produce a De facto increase in the Net Primary Productivity of the Earth's Croplands?
Despite major increases in pesticide-use in recent decades (both in tonnage and in toxicity per ton), losses to pests have increased. Some data on this follows.

Ever-increasing rate of introduction of exotic pest species, mono-cropping, the lack of strip cropping and crop rotation, ever-decreasing plant biodiversity, and other ill-advised agricultural practices all tend to counter the effects of increased pesticide use and explain the trends listed above. The overall focus in plant genetics research now appears to be that of developing new plant species with improved pest-resistances to replace previously developed species that are losing their resistance to pests that are evolving through natural selection. So far the pests are winning, and it is not clear that this will ever change, especially with all the help they are getting from ill-advised agricultural practices. Pests have the ability to evolve their pesticide-resistance about as rapidly as new pesticides can be developed. The trend toward monoculture does not just promote crop losses to pests. It also causes yields to decrease with time regardless of how much fertilizer is applied. A steady annual presence of a particular root system favors a few organisms - bacteria, fungi, nematodes - that are potagenic to plant roots. Changing to a different crop alters the circumstances, and all but the most unspecialized pathogens are unable to thrive in the absence of their usual host (90A1).

Additional evidence also suggests that pests may win this deadly race with humankind in the end. Humans apparently have limits to their ability to tolerate pesticide residues on foods, in water supplies, and airborne. In a study, researchers followed the health of 143,000 people since 1982, trying to pick out the factors that lead to diseases. They found that people regularly exposed to pesticides had a 70% higher incidence of Parkinson's disease. Gardeners who used such chemicals were as much at risk as farm workers. The findings support the idea that exposure to pesticides is a risk factor for Parkinson's Disease, a brain disease that afflicts about 150,000 Britons, with nearly 10,000 new cases per year. Scientists have suspected a link between pesticides and Parkinson's since 1983 when Californian drug addicts were diagnosed with the disease after taking impure drugs. Since then, epidemiological studies have hinted at links, but few studies have been large enough to extract meaningful figures. The latest research is big enough to get around that problem, but it raises new questions, especially which pesticides might be causing this effect. Many pesticides are designed to be toxic to animals' nervous systems, so a link with Parkinson's is not surprising ("US: Study Reveals Pesticides Link to Parkinson's," The Times (6/25/06)).

The answer to the question put forth in the title of this section is clearly NO. Expanded pesticide use cannot possibly increase the de facto Net Primary Productivity of the world's croplands.

[11] - Could the Increased Consumption of Chemical Fertilizers Produce a de facto increase in Net Primary Productivity of the World's Croplands?
Globally, per-capita consumption of inorganic (chemical) fertilizer increased five-fold during 1950-88, but dropped 23% during 1988-98 (98P2) due to elimination of subsidies in several large nations. This would suggest that the marginal productivity of chemical fertilizers had fallen to the point where it was not worth the unsubsidized price. One-third of the global increase in cereal production during the 1970s and 1980s has been attributed to increased fertilizer consumption (03B1). In the mid-19th century, Justus von Liebig formulated his "Law of the Minimum" that states that plant growth is limited by the availability of whatever nutrient is scarcest. In other words, the marginal productivity of any plant requirement (water, sunlight, nutrients) decreases with increasing dose. The marginal productivity of chemical fertilizer is now a fraction of what it was some decades ago. Some data on declining marginal productivities is given below.

Chemical fertilizer consumption per unit area of cropland in 1997 in developed countries was about 40% more than in developing countries. But the heavy usage of chemical fertilizers in the developed world comes, in no small part, from heavy European subsidies for chemical fertilizer consumption (98D1). Also, much of the consumption of chemical fertilizer is closely tied to use on genetically improved crops. These were developed especially to make them amenable to higher doses of fertilizer. In the developing world such crops are limited to high base-status soil areas of tropical Asia and tropical America (18% of the tropics, and already intensively exploited). So, even under optimal conditions, chemical fertilizer consumption per unit area of cropland in developing nations must be inherently less than in the developed world. Thus it should not be inferred that lower fertilizer consumption in developing nations means there is lots of potential for increasing fertilizer consumption in developing nations. As prices of chemical feed stocks for chemical fertilizers (mainly natural gas) increase as part of the global trend toward higher energy prices, today's low marginal productivity of chemical fertilizers translates to reduced consumption of chemical fertilizers.

To make matters worse, some previously unanticipated side effects of chemical fertilizers are now being recognized. These show that simply adding more and more fertilizer to cropland under conditions of low marginal productivity and increasing feed stock prices is increasingly unlikely to be economically justifiable, and could easily prove to be counterproductive. Excess chemical fertilizer runoffs are causing eutrophication in waterways, and dead zones in otherwise highly productive estuaries (prime fish habitats). Even worse, long-term applications of inorganic fertilizers have been found to degrade fertile temperate soils. Researchers found that soils age the equivalent of 5000 years after 30 years of normal chemical fertilizer application. Soils lose much of their ability to hold calcium, magnesium, and potassium because of increased acidity. Acidity occurs when excess nitrogen becomes nitric acid. As a result, rich temperate soils are becoming more like sandy, far less productive tropical soils (99U1). Since Western Europe uses more chemical fertilizer per unit area of cropland than almost any other nation (due to heavy subsidies), one might expect that these degrading effects would be most evident there (03A1) (00O1). The reason why this is apparently not the case is that Western Europe uses livestock manure and crop residues to provide almost half of all external nutrient inputs (03B1) and to restore the organic matter lost to the above-mentioned side-effects of chemical fertilizer. The EU's cropland soil nitrogen balance seems to be well under control even as yields increase (00O1). Unfortunately the option of using livestock manure to maintain soil organic content is being foreclosed virtually everywhere else. Most developing nations must use animal dung and crop residues as fuel for cooking, since they are unable to afford imported oil. Elsewhere, livestock is being increasingly raised in feedlots and "Concentrated Animal Feeding Operations" (CAFOs). So transportation costs of using manure to maintain cropland soil organic matter content, fertility, erosion resistance, calcium-, magnesium- and potassium levels are usually prohibitive. Feedlot- and CAFO manure must therefore be dumped in huge lagoons that tend to "accidentally" breach from time to time, releasing massive amounts of manure into streams, water supplies, etc. Thus increasing chemical fertilizer consumption in nations like the US is highly likely to become counter-productive if it is not already the case.

Sub-Saharan Africa provides an insightful case study for understanding the economics of chemical fertilizer. African soils are, by nature, poor in terms of both organic matter and nutrients. In the 1990s, China used 240 kg/ ha/ year, and India about 110, but Sub-Saharan Africa used about 8 (02F1). Chemical fertilizer prices in Sub-Saharan Africa are 6 times greater than in Asia, Europe and North America, i.e. 60 times greater in units of hours of labor required to purchase a tonne of fertilizer. Inadequate transportation infrastructure is the cause of much of the problem. Much of Sub-Saharan Africa has less than 10% of the road density of India or China (02F1). These infrastructure problems result from shortages of financial capital due largely to the need for capital to fund the infrastructure growth that high population growth rates (2.5%/ year in Africa) require. The problem in Ethiopia is similar, but with a different twist. Foreign lenders persuaded Ethiopian farmers to plant genetically improved crops but ignored the problem of inadequate transportation infrastructure. So in good years, prices of farm produce collapse, and in bad years supplies of farm produce collapse, so farmers lose money every year. The net result was that lots of Ethiopian cropland sits idle while thousands or millions of Ethiopians starve.

According to Norman E. Borlaug, Africa's grain productivity could be doubled or tripled in three years (02K1). Africa's present food deficit, plus its expected population-doubling over the next 3-4 decades, demands at least a tripling. One third of the 590 million people in Sub-Saharan Africa are chronically undernourished. Foreign food donations cover only 20% of food deficits (02K1). Sub-Saharan Africa's ever-growing external debt and extreme shortage of financial capital for solving infrastructure problems suggest that Borlaug's comments (and even the FAO's projections (03B1) out to 2030 of a 61% increase) on Sub-Saharan Africa's future grain production are likely to remain wishful thinking until more fundamental problems are addressed. The main problem is population growth that requires huge amounts of capital just to fund the infrastructure growth that population growth requires. If chemical fertilizer prices in the US were to rise by a factor of 60 to be comparable to the situation in Africa, it seems highly likely that US consumption of chemical fertilizers with their low, or negative, marginal productivities would drop dramatically in order to rebalance marginal costs against marginal productivities.

[12] - Could some Yet-to-be Discovered Procedure Increase the de facto Net Primary Productivity of the Earth's Croplands?

Plants need water, nutrients, genes and light for survival -little else. The water issue is within the irrigation issue. The nutrients issue is within the fertilizer issue. The genes issue is within the "green revolution" issue. All these issues have been analyzed. Only light remains as a potential, not-yet-addressed source of food/ fiber-productivity improvements. But this is not a variable subject to much manipulation. Replacing the sun by electric light bulbs, as in hydroponics, is capable of producing only the most expensive foods (some fruits and vegetables, but not grains - 80% of human food supplies). The notion of adding significantly to the total amount of light falling on 16 million km2 of croplands seems unrealistic. Any argument that contends that a yet-to-be-developed technology could sustainably increase food supplies should begin by defining the plant-need that the new technology is likely to serve. Since there are no un-addressed plant needs, it seems unlikely that other technologies await development.

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P. A. Sanchez, S. W. Buol, "Soils of the Tropics and the World Food Crisis", Science 188 (1975) pp. 598-603.
76B1 J. S. Bethel, G. F. Schreuder, "Forest Resources: An Overview", Science, 191 (1976) pp. 747-752.
78W1 G. M. Woodwell et al, "The Biota and the World Carbon Budget", Science, 199 (1978) pp. 141-146.
80R1 Bill Rooney, "Doing Charleston with AFA", in American Forests (February 1980) p. 14.
81C1 Council on Environmental Quality, Department of State, The Global 2000 Report to the President, Gerald O. Barney, editor, 2 (1981).
82B1 Nyle C. Brady, "Chemistry and World Food Supplies", Science, 218 (1982) pp. 847-853.
82W1 Maryla Webb, Judith Jacobsen, US Carrying Capacity: An Introduction, Carrying Capacity, Inc. (June 1982).

86P3 Donald L. Plucknett, Nigel J. H. Smith, "Sustaining Agricultural Yield", BioScience, 36 (1986) pp. 40-45.
86V1 Peter M. Vitousek, Paul R. Ehrlich, Ann H. Ehrlich, Pamela A. Matson, "Human Appropriation of the Products of Photosynthesis", BioScience, 36(6) (1986) pp. 368-373.
89B5 Lester R. Brown, "Feeding Six Billion", Worldwatch (Sept-October 1989), pp. 32-40.

90A1 Philip H. Abelson, "Opportunities in Agricultural Research", Science, 248 (1990) p. 941.
90R1 Robert Repetto, "Deforestation in the Tropics", Scientific American, 262 (April 1990) pp. 36-42.
90R2 John C. Ryan, "Timber's Last Stand", World Watch (July-August 1990) pp. 27-34.
91B1 Lester R. Brown, "Fertilizer Engine Losing Steam", Worldwatch, 4 (1991) pp. 32-33.
91P1 Sandra Postel, John C. Ryan, "Reforming Forestry", in Linda Starke, editor, State of the World 1991, W.W. Norton and Co., New York (1991) pp. 74-92.
93E1 L. T. Evans, Crop Evolution, Adaptation and Yield, Cambridge University Press (1993).
94B1 Lester R. Brown, Hal Kane, Full House: Reassessing The Earth's Population Carrying Capacity, W.W. Norton and Co., New York (1994) 262 pp.
94C1 Nancy Chege, "Africa's Non-Timber Forest Economy", World Watch (4) (1994) pp.19-23, 7
94P1 Sandra Postel, "Carrying Capacity: Earth's Bottom Line", in Linda Starke, editor, State of the World 1994, W.W. Norton and Co., New York (1994) pp. 3-21.
95P1 D. Pauly, V. Christensen, "Primary Production Required to Sustain Global Fisheries", Nature 374 (March 16 1995) pp. 255-257.

96B1 Lester R. Brown, "The Acceleration of History", in Linda Starke, editor, State of the World 1996, W.W. Norton and Co., New York (1996) pp. 3-20.
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