In the 1960s the Club of Rome and other notable commentators such as Paul Ehrlich predicted that the world's rapidly expanding population could not be fed in the near future and that mass starvation may occur. However, such dire predictions were scoffed at by many and subsequently proven wrong in the shorter term in the following decades by the Green Revolution with the introduction of high yielding crops. However, these high yields were only possible through the greater associated use of irrigation and fertilizers. Now it appears that this has come at a price, the very high price of environmental degradation that we are now paying:

• Water contamination and depletion [Water]
• Green house gas, air pollution and acid rain. [Air pollution]
• Disturbance of the nitrogen cycle [Nitrogen]
• Soil degradation [Soil]
• Deforestation [Trees]
• Loss of biodiversity [Biodiversity]
• Damage to the marine environment [Fish]

Introduction

The recent FAO report entitled Livestock's long shadow, noted
"Directly and indirectly, through grazing and through feedcrop production, the livestock sector occupies about 30 percent of the ice-free terrestrial surface on the planet. In many situations, livestock are a major source of land-based pollution, emitting nutrients and organic matter, pathogens and drug residues into rivers, lakes and coastal seas. Animals and their wastes emit gases, some of which contribute to climate change, as do land-use changes caused by demand for feedgrains and grazing land. Livestock shape entire landscapes and their demands on land for pasture and feedcrop production modify and reduce natural habitats" (Steinfeld 06).

There has been a progressive encroachment by agriculture into wild habitats causing severe fragmentation and overall loss which along with climate change has increased the species extinction rate to between a 100 and 1000 times that seen in the geological record. The recent Millennium Ecosystem Assessment noted that a third of amphibians, a fifth of mammals and eighth of bird species are now threatened by extinction in the near future (Steinfeld 06).

Vital statistics of the livestock industry overall (Steinfeld 06):

Resource consumption on a huge scale. High yielding crops are dependent of the use of large amounts of fertilizer, pesticides and water as shown in the following table (Adapted from D'Antonio 01):

Disturbance of the nitrogen cycle: it is being severely damaged by man made fertilizers and other human activities.
We have doubled the world's nitrogen supply since the invention by Haber and Bosch of artificial nitrogen fixation at the beginning of the 20th century. Recent estimates are as follows (Vitousek 97):

Soil degradation can arise from a number of processes:

• Soil erosion from tillage of crops
• Soil damage from excess water and nutrients, from pesticides and other chemicals and minerals.
• Soil compaction and erosion from hard hoofed animals and farm machinery.
• The spread of woody weeds in semi-arid and subtropical rangelands.

The global size of the problem is huge, year 2000 figures (Eswaran 01)

Soil loss from tillage of crops. Despite recent advances from the adoption of minimal or no tillage, there are still very substantial losses from erosion. Some crops are associated with greater losses because they supply less ground cover. For example soy and corn grown in rows provides less cover to prevent erosion than compared to small grained crops such as wheat which are not grown in rows. Because of the massive amounts of soy produced in the world today for intensive feed lot operations, this is a very significant problem. Soil erosion not only reduces the productivity of the land but also the run off sediment blocks drainage ditches, fills dams with silt, and pollutes streams and rivers. The problems are directly related to the amount of land under cultivation. That area has been increasing around the world in the last decades (see the above table), much of it related to the increasing use of crops to feed animals rather than being used to feed humans directly. This is very wasteful and in the longer term unsustainable.

Soil erosion increases water loss and wastage. This is probably the most significant effect of all since eroded soils are less absorbent of rain water, where more than 80% of water is lost to excessive run off. (Pimentel 04)

Soil compaction and erosion from large free-range animals Soil compaction and erosion caused by hard hoofed animals in fragile landscapes is causing substantial damage. Forage is often concentrated around water sources. Studies in the US rangelands have shown that while these riparian areas represent 1.9% of grazing land, they produce 21% of the forage and 81% of forage consumed by cattle. This concentrates the damage in this fragile zones greatly increasing erosion. Also, compaction of soil stops water penetration leading to increased run off and erosion as well as reducing aquifer replenishment. Lowering the water table then lowers stream water level, increasing the bank height and further increasing erosion from cattle, setting up a vicious cycle (Steinfeld 06).

The importance of biological crusts. Many landscapes used for cattle ranching are semi-arid lands. These usually have biological crusts formed by living organisms such as cyanobacteria, algae, lichens and mosses which protect the surface.  Hard hoofed animals readily damage them opening up such landscapes to wind and water erosion (Soilcrust 06). Compaction also damages ant nests which are an import mechanism for carrying organic matter into the subsoil and also for the penetration of water (White 97). Such processes have led to desertification in most continents especially in Australia and Africa. Local water courses are particularly hard hit by trampling, leading to murky water choked with sediment, algae and manure.

Soil compaction also occurs from agricultural machinery. This has been a significant problem in the past but due to better farming methods this has been  reduced, but in many parts of the world remains a substantial problem. The heavier the machinery, the greater the problem, not necessarily overcome with dual or balloon tyres. As agriculture has become more industrialized to meet the demands of intensive animal feedlots, machinery has tended to become much bigger for economies of scale, promoting this problem. There are many factors that can moderate this effect but good crop rotation, adding more organic matter to the soil and minimal tillage are effective measures (Compaction 06).

The spread of woody weeds is promoted by cattle grazing. Cattle are selective in what they eat, often eating down the more palatable native plants and leaving the unpalatable small woody trees along with other exotic species. Overgrazing along with competition for water and sunlight reduces ground cover grasses leading to wind and water erosion of the exposed earth.  Also cattle often distribute the seeds of these plants which become attached to their hides and the surface damage of their hooves promotes planting of the seeds. Fires which will reduce woody weeds are suppressed in an attempt to maintain pasture in the shorter term but in the longer term such moves are counterproductive. The spread of woody weeds has caused major degradation of enormous tracts of land in many countries (Steinfeld 06). The only effective measure is to reduce livestock numbers by reducing demand for animal products.

Prolonged grazing can lead to a further reduction in the existing tree cover. A survey done in Australia has shown that continuous grazing kills new tree growth with the older trees not being replaced as they die. In some areas tree numbers have dropped alarmingly. A simple answer to this is to introduce rotational grazing with individual areas intensively grazed for short periods with long periods of rest in between. (Fischer 09)

Pollution of soils by heavy metals - the roxarsone story. There has been some concern that heavy metals such as cadmium are being added to the environment through fertilizers. As small amount is added through the use of rock phosphate based fertilizers, but this is probably less important than other processes. Roxarsone is an organic arsenical compound added to chicken feed to prevent coccidial gut infections and hence acts as a general growth promoter. This compound is not absorbed by the chickens and hence there is no significant arsenic contamination of chicken products. However, the compound is passed unchanged in the litter which are then spread onto land for disposal.

What has become apparent in recent times is that there is considerable bioconversion of this compound to inorganic arsenates and arsenites. As roxarsone is water soluble, its potential to spread in ground water is large. Roxarsone is widely used around the world. More than 900 tonnes of it is released into the environment every year in the US. Chicken litter often contains 48mg/kg of arsenic. Land that has been used for such litter disposal has been shown to have substantially higher levels of arsenic. This is a cause of great concern (Cortinas 06).

Many other metals are used in intensive production units. Copper, zinc, selenium, cadmium, cobalt, iron and manganese are various used and much of this ends up as environmental contaminants (Steinfeld 06).

Salinization is a huge problem, particularly in lands where irrigation is used. Up to a third of the world's land is either affected or vulnerable.  There are a number of different mechanisms causing salinization of land: evaporation of irrigation water, rising water tables either directly from irrigation or by the removal of trees for cropping/pasture.  In rain fed crop lands, build up of salt is usually not a problem since the rain water flushes the salt away. Where water is applied to crops via irrigation, the dissolved salts in the irrigation water are progressively concentrated by the evaporation and transpiration of the applied water. This results in a paradox. Where water is applied by low volume methods such as drip irrigation, no water is available for flushing, the salt builds up. Where large volumes are used, build up of salt is reduced because of flushing (Pimentel 04).

Irrigation water can cause the water table to rise considerably. If the underlying ground has high levels of salt, this is dissolved in the rising water table and brought to the surface, eventually making the ground non-productive. Large areas of Australia, being once a inland sea, suffer from this problem. Finally, the water table can rise because of the removal of trees which keep the water table lower by extracting water which is then lost by transpiration. The rising water table brings with it large amounts of salt (White 97). Run off from these operations takes large amounts of liberated salt leading to rises in salinity of many rivers. In Australia, the Murray River is becoming more and more salty so that cities such as Adelaide closer to its mouth and which draw substantial amounts of drinking water from it, are likely to run into problems in the not too distant future.

Waterlogging from irrigation reduces productivity: water in the wrong place. Up to 60% or the water intended for the plants doesn't reach them. If drainage is not good, this water accumulates in the upper soil levels and once it has risen to root level, productivity drops. As example 8.5 million hectares of land in India are affected by this, with a reduced yield around 2 million tonnes per annum (Pimentel 04).

Deforestation.
 
Deforestation has a number of major adverse consequences. The best known is its contribution to increasing green house gases. Loss of habitat and consequent extinction of a significant proportion of the world's fauna is also a major threat. Removal of trees has several other very substantial adverse effects. It increases water run off by as much as 15% and depending on the situation, this may substantially reduce the replenishment of aquifers. In other situations it can have the reverse effect by causing a rise in the subsurface water table leading to salinization.

Deforestation leads to long term reduction in rainfall. It has recently proposed that with the cutting down of trees, the amount of transpired water vapour is proportionally reduced. Transpired water vapour condenses above forests, forming water droplets which occupy a much smaller volume than the water vapour. This then reduces air pressure so that adjacent air is drawn in. In regions that have major forests, this sucking in effect can be very substantial, drawing in moist air from the oceans to areas considerable distances inland were trees are growing. When such forests are converted to pastures or crop land, this effect is cancelled so that the rainfall is subsequently reduced. (Makarieva 09) Such a mechanism has been proposed for some of the rainfall reduction in south eastern and south western Australia, however many other regions of the world are also likely to have been adversely affected by this mechanism for example, south western USA, many parts of Africa and China. Deforestation can also reduce rainfall by other mechanisms such as the loss of air turbulance from trees and changes in albedo associated with the move to cropping/pastures.
 
Huge tracts of land have been cleared in many areas of the world for cropping and grazing. In South America, particularly in Brazil and Argentina, this has been particularly aggressive, with vast areas of land cleared either to grow soya beans to feed intensive animal production or to extend grazing land to supply the hamburger trade. Brazil lost 25,200 sq kilometres of rain forest in 2002, an area roughly 150 kilometres long by 170 kilometres wide. The area devoted to growing soy beans in Latin America more than doubled in the decade to 2004, rising to a massive 39 million hectares. This makes it the largest area for a single crop, dwarfing the 28 million hectares devoted to maize. However, the area of forest lost to the extension of grazing land in Brazil is even greater than that from crop land expansion (Steinfeld 06).  Our animal-based foods are a very poor exchange for the enormous ecological damage associated with feedcrop production and ranching in these regions.

Loss of biodiversity.

Humans have caused a massive expansion in a very limited number of species including ourselves. Less than 20 staple plant species supply the vast majority of plant-based foods and only 14 animal species supply 90% of animal-based foods. When put together, this represents a very substantial proportion of the world's biota leaving much less room for the estimated 14 million species that occupy the world.

Loss or severe degrading of the following habitats has been proceeding rapidly, much of it related to livestock production and aquaculture:

• Forests, which have the greatest overall biodiversity, are currently be cut down to extend pasture for ruminants. As example a further 24 million hectares of forest in the Amazon basin is projected to be  converted to grazing land between 2000 and 2010. Much of this expansion is occurring piecemeal fashion leading to extensive fragmentation of habitat, markedly accentuating the problem. It also makes the remnants drier in creasing their vulnerability to fire which is used in the clearing process.
  
  Many other examples of severe pressure on ecosystems can be found in South America: the tropical Andes mountain area, the Brazilian Cerrado region, the eastern Atlantic forests of Brazil, large areas of the neotropical Pampas in Argentina. These areas have enormous diversity which is threatened by this process to largely supply the hamburger and fast food broiler trade: a very poor bargain for the world.
   

• Wetlands variously drained, filled in or converted to aquaculture. Freshwater ecosystems are by far the most threatened. In the US for example 37% of freshwater fish species, 67% or mussels, 51% of crayfish and 40% of amphibians are either threatened or become extinct.
   

• Traditional farm areas which have undergone intensification causes a sharp reduction in biodiversity by a number of mechanisms. Remnant vegetation areas such as hedge rows and field edges have been removed to increase the planting area. In large monocultures of herbicide resistant crops, herbicides eliminate not only weeds but also anything else which in turn eliminates many insect and bird species. Many pastures are planted with single grass species and weeds controlled with herbicides to increase livestock yields, markedly reducing the plant community diversity.
   

• Traditional farmland which has been abandoned or set aside under the general push for intensification. These lands quite often revert to scrub cover of very low biodiversity rather than regenerating into diverse forest regions. There is a conversion of the previous diverse pasture biota to a much more limited one associated with woody weed invasion.
   

• Rangelands, particularly the dry and semi-arid marginal lands are extensively damaged by livestock causing significant species loss, through erosion, desertification and woody weed invasion.

Other mechanisms of loss of biodiversity.

• Competition with wildlife through either predation or competition over food and water, particularly in Africa. In areas of Europe and North America, large predators have been re-introduced leading to conflict with ranch owners.

• Reliance on a very small number of breeds suitable for industrial scale production has led to the loss of a large number of earlier breeds. In Europe, 55% of mammalian breeds and 69% of avian breeds have either become extinct or are endangered. This represents a concerning loss of genetic stock. For example in the US, 90% of milk comes from one breed, Holstein-Friesian and 90% of eggs from White Leghorns (Steinfeld 06). This contraction of the gene pool may have major adverse effects if future living conditions change markedly such as with climate change.

• Pollution particularly of the marine environment has led to marked changes in the pre-existing flora and fauna often associated with algal blooms and toxic dinoflagellates from eutrophication. Also see the section on dead zones. Toxins from algal blooms can affect a very wide range of organisms from shell fish to sea birds to cetaceans. Coral reefs are particularly vulnerable to eutrophication. Eutrophication related zooplankton increase has been the main driver of the massive expansion of jelly fish populations in many areas of the world, causing numerous problems.
  Acid rain has greatly affected biodiversity in freshwater habitats. Pollution from veterinary medicines such as growth promoters, hormones, antibiotics and other medicines. Veterinary use of the anti-inflammatory drug diclofenac almost wiped out Indian subcontinent vultures.

Damage to the marine environment. Current fishing practices are:

• At the limit of their capacity
• Damaging the sea bed and injuring birdlife and large marine animals.
• With the use of marine aquaculture, further depleting wild fish stocks, polluting the seas and damaging coastal habitats.
• Promoting vast blooms of jellyfish which in turn further decrease fish stocks.

Many fisheries are in steep decline or have been wiped out. Globally, the number of fishery collapses (defined as catches less than 10% or the historic maximum) have  been accelerating with 29% of fisheries in large marine ecosystems in this category in 2003. If individual fish taxa are considered, around 65% of species are in this category (Worm 06).

 
Graph A showing the progressive decline in fish stocks. The top curve represents the yearly rate of numbers of collapsed taxa and the bottom shows the cumulative loss. The insert B shows the worldwide distribution of the number of species, indicating a falling diversity is most regions. (From Worm 06)

The overall catch has declined more slowly because as fishing fleets having depleted one species they move onto another thus tending to maintain the overall catch.  As example, following the collapse of the Canadian cod fishery, the number of crustaceans caught increased substantially. Most fisheries are below their historic maximum catches, for example Canada at 40%, US at 55% and the EU at 60% (Hilborn 03) forcing the large European fleets to move further afield. Worldwide, despite large increases in fishing effort, cumulative yields across all species has declined by 13% since the peak in 1994 (Worm 06). Further evidence has been illustrated recently on the Good website (www.good.is) with the following transparency.

Some commentators argue that this doesn't necessarily indicate that these fisheries will collapse but instead a new equilibrium will be gained with lower or different catches. This can be seen in the highly exploited Mediterranean (Hilborn 03). However, many disagree with such assessments.  For an excellent review of the negative aspects of world wide fisheries, download "Fish Dish: Exposing the unacceptable face of seafood" from the World Wildlife Fund site (WWF 06). If for example the exhortations to eat more fish as part of a healthy diet were put into effect, serious short falls in supply would occur and the temptation to over exploit would increase. Current estimates would indicate that if major conservation programs are not put in place to conserve major marine fish stocks, close to 100% of all fisheries will collapse by the mid 21st century (Worm 06).

Some fishing policies to conserve numbers has had unexpected consequences. Setting size limits in an attempt to maintain populations selectively removes the larger more mature fish. Breeding success has been noted to rise exponentially with size with the largest older fish having a much higher breeding success rate, often orders of magnitude greater. This has been one of the reasons for steep declines in some fish numbers. A solution taken up by some fishery regulators is to establish substantial no-fishing zones, where older and much larger mature breeding stock is left undisturbed allowing their hatchlings radiating out from these zones. (Birkehead 05)(Worm 06).

Many fishing practices are very destructive. Problems relate to the discarding of undersize fish and other unmarketable species which rarely survive the trauma of being caught. Removal of large numbers of a particular type of fish may also cause a permanent alteration in the ecology so that predators previously eaten by the fish now eat the young of that fish. This is thought to be one of the major reasons why cod fisheries have not recovered with an explosion in crab numbers. Added to this is when many new fishing zones are exploited, no consideration is given as to how long these fish take to develop to breeding maturity.

Many fish types take surprisingly long times of decades to reach this stage and are readily threatened by even moderate fishing such as the orange roughy or the Patagonian tooth fish. Finally high demand and high prices have led to the use of cyanide fishing practiced illegally in many parts of SE Asia which lays waste to the whole environment. Often times these people are forced into this situation through desperation because of declining fish stocks associated with poorly regulated industrial fishing.

Exploitation of remote fisheries continues apace with little benefit to the local inhabitants. As example, the fisheries off Kiribati in the Pacific are now being very heavily fished by boats from China, Taiwan, and Europe extracting billions of dollars of fish, but giving a paltry few million to the local community. As an added "bonus", the fleets have bought sexual exploitation and HIV to the local community (Bohane 06). Since the dramatic decline of North Sea fisheries, European government subsidized fleets have spread much further afield, wreaking havoc on coastal fisheries of distant countries. These fleets off the west coast of Africa have significantly reduced the catch of the local fishermen, who have in turn boosted their protein intake from bush meat, leading to the subsequent further alarming decline of many endangered land animals through the bushmeat trade (Brashares 04). Industrial fishing off the coast of Chile has severely affected the local fisheries so that many have now turned to environmentally more damaging aquaculture.

The damage done by bottom trawling has only recently been appreciated. Because no one in the past looked very carefully, the damage done to sea bed habitats was ignored. Recent studies have shown long term damage in places to these fragile habitats and a minority of may recover (Hilborn 03). However, most sustain substantial damage with a reduction of species richness which in turn reduces productivity(Worm 06). Bottom trawling lead to a permanent change in the marine fauna, with scavenger species favoured. This leads to further pressure on other species because of predation on juveniles. Many jurisdictions have imposed controls on this type of fishery but in less well regulated parts of the world, it remains a significant problem.

Injury to wild life has been extensive. This has been widely publicized and public pressure has been placed pressure on some fisheries, many problems remain. The killing of dolphins and large seabirds has been highlighted and while some changes have occurred, much is still to be done. Here are some examples of the massive toll on wildlife (WWF 06):

Even though there have many advances in aquaculture, the problems of industrial scale farming also apply to aquaculture. It should be noted at the outset, the majority of farmed fish in the world, located predominantly in China, are fresh water vegetarian species and are much more environmentally acceptable. Most of the the table fish favoured in the west are carnivorous. Feeding fish to fish has always seemed wasteful of natural resources, with around 3kg of feed for every kg of farmed salmon. However, with some species fishmeal is being augmented with vegetable protein lowering the pressure on the supply of fish for fishmeal, but this has the negative effect of reducing omega 3 levels. Many of the improvements in food conversion ratios has been because of the increasing proportion of fish oil in feed, but this can alter the flavour of the fish considerably.

The industry and those that advise it feel that fishmeal fisheries are sustainable but many others express doubts. Around 53% of fishmeal world wide is fed to farm animals, 29% to pigs and 24% to poultry (Steinfeld 06). Such a use is a great concern in relation to sustainability. While the proportion used by poultry has fallen in the past two decades, there is still increasing demand from the expanding pig industry. While fish meal only forms a very small proportion of pig feed, it is a highly valued protein input particularly in the early weaned stage of development.

Statistics show that world fishmeal supplies have remained relatively constant for the past 15 years where as farmed fish outputs have increased three fold in the same period. Part of the explanation for this may be that most of the fish stocks used for fishmeal such as sardines, anchovies and capelin, are close to full exploitation, requiring increasing diversion from animal feed uses. However, there is evidence of illegal fishing to bypass the quotas set by many countries to maintain supply in the face of heavy demand. Significant local problems have arisen in association with these fisheries. Reduction in small fish numbers in Chilean waters in part associated with heavy fishing to supply fish farms has led to a substantial reduction in sea bird numbers. Other major environmental problems are shown in the following table:

For an extensive and balanced review of aquaculture of carnivorous fish see the Seaweb report (Seaweb 03). 

 
Shrimp farming has been associated with the broad scale destruction of mangrove habitats particularly in south east Asia. This leads to several more problems: the increased vulnerability of these coasts to typhoons and tsunami, the extensive loss of fish breeding habitat and extensive pollution.

Overfishing has led to vast jellyfish blooms and declines in fish stocks. In recent years, huge jellyfish blooms have appeared in many parts of the world such as The Gulf of Mexico, The Mediterranean, The North Sea, The Sea of Japan and many parts of S-E Asia. Many fish species feed on junvenile jellyfish and the loss of these predators has allowed jelly fish numbers to increase markedly. In turn, the jellyfish then compete with juvenile fish for plankton and other food sources further reducing fish numbers. For example, sardines target juvenile jellyfish and the massive harvesting of sardines in part for aquaculture has led to a rapid decline in their numbers with a simultaneous increase in jellyfish. Eutrophication has also been a factor in the increase of jellyfish. Jellyfish blooms damage fishing nets, harm fish farms, imperil tourism because swimming becomes unpleasant or dangerous as well as reducing food supply for many communities.Only very small amounts of jellyfish are harvested for human consumption. (Richardson 09)

[Top]

(Birkehead 05) Charles Birkeland, Paul K. Dayton. The importance in fishery management of leaving the big ones. Trends in Ecology and Evolution 2005;20: 356-358.

(Bohane 06) Ben Bohane. Tiniest nations caught in the net. Sydney Morning Herald 2006 9th October.

(Bousquet 06) P. Bousquet, P Ciais et al. Contribution of anthropogenic and natural sources to atmospheric methane variability. Nature 2006; 443:439-443

(Brashares 04) Justin S. Brashares, Peter Arcese, Moses K. Sam, Peter B. Coppolillo, A. R. E. Sinclair, Andrew Balmford. Bushmeat Hunting, Wildlife Declines, and Fish Supply in West Africa. Science 2004;306:1180-1183

(Compaction 06) University of Nebraska. Management to minimize and reduce soil compaction. Web site at www.ianrpubs.unl.edu

(Cortinas 06) Irail Cortinas, Jim A Field, Mike Kopplin, John R. Garbarino, A.Jay Gandolfi, Reyes Sierra-Alvarez. Anaerobic Biotransformation of Roxarsone and Related N-Substituted Phenylarsonic Acids. Environ. Sci. Technol. 2006, 40, 2951-2957

(D'Antonio 01) Carla D’Antonio, Andrew Dobson, Robert Howarth, David Schindler, William H. Schlesinger, Daniel Simberloff, Deborah Swackhamer. Forecasting Agriculturally Driven Global Environmental Change. Science 2001;292:281-282

(Eswaran 01) Eswaran, H., R. Lal  P.F. Reich.  Land degradation: an overview. In: Bridges, E.M., I.D. Hannam, L.R. Oldeman, F.W.T. Pening de Vries, S.J. Scherr, and S. Sompatpanit (eds.). Responses to Land Degradation. Proc. 2nd. International Conference on Land Degradation and Desertification, Khon Kaen, Thailand. 2001 Oxford Press (Available on the USDA/NRCS Soils web site www.soils.usda.gov )

(Fischer 09) Joern Fischer, Jenny Stott, Andre Zerger, Garth Warren, Kate Sherren, and Robert I. Forrester. Reversing a tree regeneration crisis in an endangered ecoregion. PNAS 2009; doi/10.1073/pnas.0900110106

(Hanson 06) Jim Hanson. The threat to the planet. Actions required to avert dangerous climate change. Presentation to SOLAR 2006, Denver Colorado.

(Hiborn 03) Ray Hilborn, Trevor A. Branch, Billy Ernst, Arni Magnusson, Carolina V. Minte-Vera, Mark D. Scheuerell, Juan L. Valero. State of the World's Fisheries. Annu. Rev. Environ. Resour. 2003; 28:359–99

(Jacobson 06) Michael Jacobson. Six arguments for a greener diet. Center for Science in the Public Interest 2006, page 81.

(Makareva 09) Anastassia M. Makarieva , Victor G. Gorshkov , Bai-Lian Li. Precipitation on land versus distance from the ocean: Evidence for a forest pump of atmospheric moisture. Ecological Complexity 2009, DOI: 10.1016/j.ecocom.2008.11.004

(McMichael 07) Anthony J McMichael, John W Powles, Colin D Butler, Ricardo Uauy. Food, livestock production, energy, climate change, and health. Lancet 2007; DOI:10.1016/S0140-6736(07)61256-2

(Pimentel 04) David Pimentel, Bonnie Berger, David Filiberto, Michelle Newton, Benjamin Wolfe, Elizabeth Karabinakis, Steven Clark, Elaine Poon, ELizabeth Abbett, Sudha Nandagopal. Water Resources: Agricultural and Environmental Issues. Bioscience 2004; 54: 909-918

(Seaweb 03) MIchael Webber. What price farmed fish: a review of the environment and social costs of farming carnivorous fish. This can be downloaded from www.seaweb.org in the section on Aquaculture feeds and resources.

(Soilcrust 06) US Geological Survey web site on soil crusts. www.soilcrust.org/crust101.htm

(Steinfeld 06) Henning Steinfeld, Pierre Gerber, Tom Wassenaar, Vincent Castel, Mauricio Rosales, Cess de Haan. Livestock's long shadow: environmental issues and options. LEAD/FAO publication 2006. Downloadable from http://www.fao.org/docrep/010/a0701e/a0701e00.HTM

(Richardson 09) Anthony J. Richardson, Andrew Bakun, Graeme C. Hays, Mark J. Gibbons. The jellyfish joyride: causes, consequences and management responses to a more gelatinous future. Trends in Ecology and Evolution 2009;24: 312-322

(Vitousek 97) Peter M. Vitousek,  John Aber, Robert W. Howarth, Gene E. Likens, Pamela A. Matson, David W. Schindler, William H. Schlesinger, G. David Tilman. Human Alteration of the Global Nitrogen Cycle: Causes and Consequences. Issues in Ecology 1997;No1:1-16.

(White 97) Mary E. White. LIsten-Our Land is Crying. 1997 Kangaroo Press.

(Worm 06) Boris Worm, Edward B. Barbier, Nicola Beaumont, J. Emmett Duffy, Carl Folke,  Benjamin S. Halpern, Jeremy B. C. Jackson,  Heike K. Lotze, Fiorenza Micheli,  Stephen R. Palumbi,  Enric Sala,8 Kimberley A. Selkoe, John J. Stachowicz,  Reg Watson. Impacts of Biodiversity Loss on Ocean Ecosystem Services. Science 2006; 314:787-790.

(WWF 06) World Wildlife Fund. Fish dish: Exposing the unacceptable face of seafood. 2006. www.panda.org. in the publications listed in the marine section.