The world is faced with a triple crisis: climate change, peak oil and global resource depletion. These are interrelated and interactive problems which makes the subject extremely complex. The certainties are that there will be great changes to contend with in the future in order to produce and deliver food to maintain the present world population, let alone a balanced diet for everyone. At the present time there are roughly one billion people that are underfed and/or on imbalanced diets lacking essential micro nutrients that are provided by animal protein.
 
The primary resource depletion is that of fossil fuel energy since the world has been using more fossil energy than is being discovered and it appears that the reserves of oil that can be cheaply mined are now at peak production (half these resources have been combusted). As oil reserves are depleted it is predictable that, just as with any other commodity, prices will rise with increasing scarcity. World population expansion has been promoted by the availability of inexpensive oil, which has supported increased world food production by providing inexpensive inputs including fertilizers, insecticides, herbicides, traction power( lowering the need for labour and reducing the numbers of people in farming) and in places irrigation water. Inexpensive oil allowed food to be produced cheaply but this will change greatly as oil prices rise creating the potential for major disruptions in food availability.
 
Peak oil represents a massive change and will affect other resource availabilities. Agriculture has received inexpensive fertilizers on which high crop yields have been predicated including

• nitrogen fertilizers as urea manufactured using natural gas as the major energy source, 
• phosphates,   the world is now dependent on extracting phosphate fertilizers from low grade rock phosphate at high energy costs and phosphorus availability is in decline 
• Potassium, which is mined in a number of countries  

The dependency of the industrialized countries on oil to drive agricultural production and the fact that most of these same countries cannot meet their own domestic requirements from local resources has seen a headlong development of alternative fuels including bioethanol produced from sugar cane and maize mainly in Brazil and the USA, respectively; and development of bio diesel from plant oils. The implications for world food stocks and prices are enormous, potentially creating major cereal food /feed grain shortages as land is diverted to fuel production. The expectations are that world cereal grain availability for livestock will be highly restricted and the case is made for the forage-fed ruminant as a major source of animal protein for the future. Herbivores in general are likely to be used more extensively with time, particularly the rabbit with its dual capabilities of high reproduction rates and the capacity to utilize efficiently forage resources produced locally.
 
Biofuels production diverts land from food production to transportation energy and often the land is accessed from clearing of forests with often dramatic effects on biodiversity, erosion and the carbon balance of the land area.
 
Water is the other major resource required for agriculture, which has also been depleted. Fossil ground water (water created as the world cooled many millions of years ago) has been exploited using cheap fuel, but most fossil resources are now too deep to be economically mined for irrigation reducing some of the major areas of crop production (eg:  The U.S. Ogallala aquifer and the aquifer under the North China Plain). Many of the world’s aquifers that were normally replenished by rainfall have also been drawn down with periodic loss of irrigation potential   The advent of Peak Oil with ultimate high cost of fuel will clearly cause a return of vast areas of highly productive irrigated crop land back to rainfed cropping, pasture  or desert  in the future with major loss of food productivity.
 
Soil erosion and fertilizer run off from cropping systems are also major concerns as the present day cereal crops only tap the nutrients in the top few inches of soil and even the prairies of USA which have been only cropped for about 100 years have depleted the top soil reserves with potential to decrease crop yields significantly. 
 
Global warming is now accepted as real and cannot be ignored in any discussion on future agriculture. Increasing sea levels will undoubtedly remove considerable areas of fertile delta and weather patterns will certainly change, leading to at times more intense drought and or flooding rains. Warming also carries with it the risk of decreased crop production as recent research has demonstrated that rice yields decrease by 10 per cent for every ^oC rise in night time temperatures.
 
Each aspect of this triple global crisis has the potential to lower world crop production by direct or various flow on effects. We must now enter a stage in the world where grain-based animal production will become increasingly expensive as the competition for resources for food, feed and fuel, develops. The animal production industries based on herbivores will need extensive development exploiting a wide range of waste byproducts of agriculture or from land not dedicated to food or biofuels production.
 
Oil depletion, pressure to produce biofuels, soil fertility decline (including salinity and sodicity) the high cost of chemical fertilizers and the loss of arable land to erosion, non agricultural purposes (such as roads and houses), coupled with likely overall decreases in crop production from global warming, all appear to be interacting such that it will be difficult for many nations to feed themselves in the future. The developing countries seen by some as backward in agriculture may be those most capable of supporting themselves through the maintenance of small-scale farmer practices that integrate food and fuel production.