A Malthusian catastrophe (sometimes called a Malthusian check, Malthusian crisis, Malthusian dilemma, Malthusian disaster, Malthusian trap, Malthusian controls or Malthusian limit) is a return to subsistence-level conditions as a result of population growth outpacing agricultural production.
Why should I be aware of this?
The United Nations projects a population of eight billion people by 2025. The growing population is also becoming more prosperous. The average person is consuming more food, water, metal and power. Growing numbers of China's and India’s billions are stepping up to the middle class, adopting the high-protein diets, gasoline-fueled transport and electric gadgets that developed nations enjoy.
This has resulted in phenomenal increase in demand for resources and if supplies don't keep pace, prices are likely to climb further, economic growth in rich and poor nations alike could suffer, and some fear, there would be violent conflicts.
All about Malthusian catastrophe
The Malthusian catastrophe concept was introduced in 1798 by Thomas Malthus in An Essay on the Principle of Population, in which he pointed out that human populations tend to grow exponentially, while the capabilities of agricultural resources tend to grow arithmetically. Based on this pattern, overconsumption by the human population would outstrip agricultural ability. Malthus predicted that this state would trigger radical social changes, including population decline and a state of misery.
Population growth vs. food supply
Thomas Malthus'essay was based on the theory that population, if unchecked, increases at a geometric rate, whereas the food supply could only grow at an arithmetic rate. Mathematically, any increasing geometric sequence (e.g. 1, 3, 9, 27, 81) will eventually overtake all arithmetic sequences (e.g. 10, 20, 30, 40, 50). The resulting decrease in food per person will eventually lead to subsistence-level conditions. According to Malthus, the catastrophe can only be prevented by self-restraint or vice—which for him included contraception and abortion.
Malthus did not give a time frame for his catastrophe. Thus far, population growth has been essentially geometric as Malthus predicted. The Malthusian catastrophe, however, has not occurred, principally because food supply growth has also been roughly geometric, not arithmetic. Furthermore, the widespread use of contraception and abortion (Malthusian vices) has, as Malthus said they could, restrained population growth significantly. In fact currently food supply per person is several times higher than when Malthus wrote his essay.
- Some of the resources now in great demand have no substitutes. In the 18th century, England responded to dwindling timber supplies by shifting to abundant coal. But there can be no such replacement for arable land and fresh water. 
In the past, economic forces spurred solutions. Scarcity of resource led to higher prices, and higher prices eventually led to conservation and innovation. Whale oil was a popular source of lighting in the 19th century. Prices soared in the middle of the century, and people sought other ways to fuel lamps. In 1846, Abraham Gesner began developing kerosene, a cleaner-burning alternative. By the end of the century, whale oil cost less than it did in 1831. 
As a result of globalization, some constraints might disappear. Where some countries face scarcity, others have bountiful supplies of resources. New seed varieties and better irrigation techniques could open up arid regions to cultivation that today are only suitable as hardscrabble pasture. Technological breakthroughs, like cheaper desalination or efficient ways to transmit electricity from unpopulated areas rich with sunlight or wind, could brighten the outlook. 
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