Question: By what percentage is the maize crop in Souther Africa going to decrease by 2030?
About the article "Global warming", section "Food security".

Candidate passages:
Under present trends, by 2030, maize production in Southern Africa could decrease by up to 30%, while rice, millet and maize in South Asia could decrease by up to 10%.
By 2080, yields in developing countries could decrease by 10% to 25% on average while India could see a drop of 30% to 40%.
By 2100, while the population of three billion is expected to double, rice and maize yields in the tropics are expected to decrease by 20–40% because of higher temperatures without accounting for the decrease in yields as a result of soil moisture and water supplies stressed by rising temperatures.
Future warming of around (by 2100, relative to 1990–2000) could result in increased crop yields in mid- and high-latitude areas, but in low-latitude areas, yields could decline, increasing the risk of malnutrition.
A similar regional pattern of net benefits and costs could occur for economic (market-sector) effects.
Warming above could result in crop yields falling in temperate regions, leading to a reduction in global food production.
  Set in 2030: * "2030: A Day in The Life of Tomorrow's Kids" (Amy Zuckerman and James Daly; Dutton Children's Books; 2009) * "2030 : The Real Story of What Happens to America", a 2011 novel by Albert Brooks  
[[File:Corn and soybean temperature response (ARS USDA).png|thumb|350px|left|alt=refer to caption and image description|For each plant variety, there is an optimal temperature for vegetative growth, with growth dropping off as temperatures increase or decrease.
Similarly, there is a range of temperatures at which a plant will produce seed.
Outside of this range, the plant will not reproduce.
As the graphs show, corn will fail to reproduce at temperatures above 95 °F and soybean above 102 °F.
]]Despite technological advances, such as improved varieties, genetically modified organisms, and irrigation systems, weather is still a key factor in agricultural productivity, as well as soil properties and natural communities.
The effect of climate on agriculture is related to variabilities in local climates rather than in global climate patterns.
The Earth's average surface temperature has increased by 1.5°F (0.83°C) since 1880.
Consequently, agronomists consider any assessment has to be individually consider each local area.
On the other hand, agricultural trade has grown in recent years, and now provides significant amounts of food, on a national level to major importing countries, as well as comfortable income to exporting ones.
The international aspect of trade and security in terms of food implies the need to also consider the effects of climate change on a global scale.
A study published in "Science" suggests that, due to climate change, "southern Africa could lose more than 30% of its main crop, maize, by 2030.
In South Asia losses of many regional staples, such as rice, millet and maize could top 10%".
The Intergovernmental Panel on Climate Change (IPCC) has produced several reports that have assessed the scientific literature on climate change.
The IPCC Third Assessment Report, published in 2001, concluded that the poorest countries would be hardest hit, with reductions in crop yields in most tropical and sub-tropical regions due to decreased water availability, and new or changed insect pest incidence.
In Africa and Latin America many rainfed crops are near their maximum temperature tolerance, so that yields are likely to fall sharply for even small climate changes; falls in agricultural productivity of up to 30% over the 21st century are projected.
Marine life and the fishing industry will also be severely affected in some places.
Climate change induced by increasing greenhouse gases is likely to affect crops differently from region to region.
For example, average crop yield is expected to drop down to 50% in Pakistan according to the UKMO scenario whereas corn production in Europe is expected to grow up to 25% in optimum hydrologic conditions.
More favourable effects on yield tend to depend to a large extent on realization of the potentially beneficial effects of carbon dioxide on crop growth and increase of efficiency in water use.
Decrease in potential yields is likely to be caused by shortening of the growing period, decrease in water availability and poor vernalization.
In the long run, the climatic change could affect agriculture in several ways :  "productivity", in terms of quantity and quality of crops  "agricultural practices", through changes of water use (irrigation) and agricultural inputs such as herbicides, insecticides and fertilizers  "environmental effects", in particular in relation of frequency and intensity of soil drainage (leading to nitrogen leaching), soil erosion, reduction of crop diversity  "rural space", through the loss and gain of cultivated lands, land speculation, land renunciation, and hydraulic amenities.
"adaptation", organisms may become more or less competitive, as well as humans may develop urgency to develop more competitive organisms, such as flood resistant or salt resistant varieties of rice.
They are large uncertainties to uncover, particularly because there is lack of information on many specific local regions, and include the uncertainties on magnitude of climate change, the effects of technological changes on productivity, global food demands, and the numerous possibilities of adaptation.
Most agronomists believe that agricultural production will be mostly affected by the severity and pace of climate change, not so much by gradual trends in climate.
If change is gradual, there may be enough time for biota adjustment.
Rapid climate change, however, could harm agriculture in many countries, especially those that are already suffering from rather poor soil and climate conditions, because there is less time for optimum natural selection and adaption.
But much remains unknown about exactly how climate change may affect farming and food security, in part because the role of farmer behaviour is poorly captured by crop-climate models.
For instance, Evan Fraser, a geographer at the University of Guelph in Ontario Canada, has conducted a number of studies that show that the socio-economic context of farming may play a huge role in determining whether a drought has a major, or an insignificant impact on crop production.
In some cases, it seems that even minor droughts have big impacts on food security (such as what happened in Ethiopia in the early 1980s where a minor drought triggered a massive famine), versus cases where even relatively large weather related problems were adapted to without much hardship.
Evan Fraser combines socio-economic models along with climatic models to identify “vulnerability hotspots” One such study has identified US maize (corn) production as particularly vulnerable to climate change because it is expected to be exposed to worse droughts, but it does not have the socio-economic conditions that suggest farmers will adapt to these changing conditions. 
The word "maize" derives from the Spanish form of the indigenous Taíno word for the plant, "maiz".
It is known by other names around the world.
"Corn" outside North America, Australia, and New Zealand means any cereal crop, its meaning understood to vary geographically to refer to the local staple.
In the United States, Canada, Australia, and New Zealand, "corn" primarily means maize; this usage started as a shortening of "Indian corn".
"Indian corn" primarily means maize (the staple grain of indigenous Americans), but can refer more specifically to multicolored "flint corn" used for decoration.
In places outside North America, Australia, and New Zealand, "corn" often refers to maize in culinary contexts.
The narrower meaning is usually indicated by some additional word, as in "sweet corn", "corn on the cob", "popcorn", "corn flakes", "baby corn".
In Southern Africa, maize is commonly called "mielie" (Afrikaans) or "mealie" (English).
"Maize" is preferred in formal, scientific, and international usage because it refers specifically to this one grain, unlike "corn", which has a complex variety of meanings that vary by context and geographic region.
"Maize" is used by agricultural bodies and research institutes such as the FAO and CSIRO.
National agricultural and industry associations often include the word "maize" in their name even in English-speaking countries where the local, informal word is something other than "maize"; for example, the Maize Association of Australia, the Indian Maize Development Association, the Kenya Maize Consortium and Maize Breeders Network, the National Maize Association of Nigeria, the Zimbabwe Seed Maize Association.
However, in commodities trading, "corn" consistently refers to maize and not other grains. 
"Feed maize" is being used increasingly for heating; specialized corn stoves (similar to wood stoves) are available and use either feed maize or wood pellets to generate heat.
Maize cobs are also used as a biomass fuel source.
Maize is relatively cheap and home-heating furnaces have been developed which use maize kernels as a fuel.
They feature a large hopper that feeds the uniformly sized maize kernels (or wood pellets or cherry pits) into the fire.
Maize is increasingly used as a feedstock for the production of ethanol fuel.
Ethanol is mixed with gasoline to decrease the amount of pollutants emitted when used to fuel motor vehicles.
High fuel prices in mid-2007 led to higher demand for ethanol, which in turn lead to higher prices paid to farmers for maize.
This led to the 2007 harvest being one of the most profitable maize crops in modern history for farmers.
Because of the relationship between fuel and maize, prices paid for the crop now tend to track the price of oil.
The price of food is affected to a certain degree by the use of maize for biofuel production.
The cost of transportation, production, and marketing are a large portion (80%) of the price of food in the United States.
Higher energy costs affect these costs, especially transportation.
The increase in food prices the consumer has been seeing is mainly due to the higher energy cost.
The effect of biofuel production on other food crop prices is indirect.
Use of maize for biofuel production increases the demand, and therefore price of maize.
This, in turn, results in farm acreage being diverted from other food crops to maize production.
This reduces the supply of the other food crops and increases their prices.
Maize is widely used in Germany as a feedstock for biogas plants.
Here the maize is harvested, shredded then placed in silage clamps from which it is fed into the biogas plants.
This process makes use of the whole plant rather than simply using the kernels as in the production of fuel ethanol.
A biomass gasification power plant in Strem near Güssing, Burgenland, Austria, began in 2005.
Research is being done to make diesel out of the biogas by the Fischer Tropsch method.
Increasingly, ethanol is being used at low concentrations (10% or less) as an additive in gasoline (gasohol) for motor fuels to increase the octane rating, lower pollutants, and reduce petroleum use (what is nowadays also known as "biofuels" and has been generating an intense debate regarding the human beings' necessity of new sources of energy, on the one hand, and the need to maintain, in regions such as Latin America, the food habits and culture which has been the essence of civilizations such as the one originated in Mesoamerica; the entry, January 2008, of maize among the commercial agreements of NAFTA has increased this debate, considering the bad labor conditions of workers in the fields, and mainly the fact that NAFTA "opened the doors to the import of maize from the United States, where the farmers who grow it receive multimillion dollar subsidies and other government supports.
(...) According to OXFAM UK, after NAFTA went into effect, the price of maize in Mexico fell 70% between 1994 and 2001.
The number of farm jobs dropped as well: from 8.1 million in 1993 to 6.8 million in 2002.
Many of those who found themselves without work were small-scale maize growers.").
However, introduction in the northern latitudes of the U.S. of tropical maize for biofuels, and not for human or animal consumption, may potentially alleviate this.
As a result of the U.S. federal government announcing its production target of of biofuels by 2017, ethanol production will grow to by 2010, up from 4.5 billion in 2006, boosting ethanol's share of maize demand in the U.S. from 22.6 percent to 36.1 percent.