Question: By how much is the maize production in Southern Africa predicted to decreade by 2030?
About the article "Global warming", section "Food security".

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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.
Cicadulina is a leafhopper genus in the tribe Macrostelini.
"Cicadulina" species are vectors of the maize streak virus, a disease which is a sporadic but severe in sub-Saharan Africa.
The cause is a geminivirus which is persistently transmitted by "Cicadulina" leafhoppers.
The disease is also transmitted to "Urochloa panicoides", a fodder grass originating in Southern Africa.
The maize orange leafhopper "Cicadulina bipunctata" has been reported to induce gall-like structures on maize in Japan 
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. 
[[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. 
Urbanisation from the nineteenth century onward, coupled with close control over agricultural production, led Black South Africans to rely more and more on comparatively expensive, industrially-processed foodstuffs like wheat flour, white rice, mealie-meal (maize) and sugar.
Before the arrival of crops from the Americas, "pap" was mostly made from sorghum, but maize is much more prevalent today.
Often these foods were imported or processed by white wholesalers, mills and factories.
The consequence was to drastically restrict the range of ingredients and cooking styles used by indigenous cooks.
On the other hand, some imported food plants (maize, tomatoes) have expanded the dietary range of indigenous cooks.
Of these maize is the most significant - it has been integrated to such an extent into the traditional diet that it is often assumed to be an indigenous plant.
Popular foods in modern South Africa are chicken, limes, garlic, ginger, chili, tomatoes, onions and many spices.