Projections
In 2001, the IPCC stressed that the poorest countries would be hardest hit with sharp reductions in crop yields in many tropical and subtropical regions due to difficulty in bringing in water and new insect pests.
While local benefits from global warming could be felt in some regions (such as Siberia), more recent evidence says that global crop yields will be negatively affected.[14].
In 2007, Schneider et al.[15] projected that an increase of 1 to 3 °C would produce a decrease in the production of some cereals at low latitudes and an increase in production at high latitudes, and in general global production would increase up to a rise of approximately 3 °C, and would probably decrease if it exceeds the level of 3 and 4 °C. Many of the world agriculture studies done by Schneider et al. They do not include critical factors such as extreme changes or the spread of pests and diseases. Studies have also not considered the development of specific techniques or technologies that help adaptation. In 2007, increased incentives for farmers to grow non-food biofuel products[16] along with other factors (such as rising transportation costs, climate change, increased consumer demand in China and India, and population growth) caused food shortages in Asia, the Middle East, Africa, and Mexico, as well as rising food prices around the world. As of December 2007, 37 countries are facing food crises and 20 have imposed some form of price controls on food.
Another important point to consider is that undesirable grasses also carry out the same cycle as crops and therefore would also benefit from carbon fertilization. Since most weeds are C3 plants (They are called that because in C3 type the first organic compound made in photosynthesis has 3 carbon atoms and in C4 type it has 4), they are competing against C4 crops such as tomatoes. However, some results make it possible to think that herbicides can gain in effectiveness with increasing temperature.
Global warming could cause an increase in precipitation in some areas, leading to an increase in atmospheric humidity and the length of wet seasons. Combined this with high temperatures, it could favor the development of fungal diseases. The state of Barinas (Venezuela) is suffering from this effect, especially in the cultivation of cassava. The increase in temperature and humidity is also favoring the increase in insect pests.
Africa's geography makes it particularly vulnerable to climate change and 70% of the population relies on rainfed agriculture for their subsistence. An official Tanzanian report on climate change suggests that areas that typically have 2 rainfall a year will likely have more and those that only have one rainfall season could have much less rainfall. The expected net result is that 33% less corn (the country's staple food) will grow.[17] Along with other factors, regional climate change, specifically decreased rainfall, is believed to have contributed to the Darfur Conflict.[18] The combination of decades of drought, desertification and overpopulation are the causes of the conflict, as the nomadic Baggara people's search for water forces them to move their livestock further south, to lands occupied primarily by farmers.[19].
With high probability, the IPCC concluded that climate variability and change would seriously compromise agricultural production and access to food.[20] Some studies argue that southern Africa could lose more than 30% of its main crop, maize, by 2030.
Climate change may be one of the causes of conflict in Darfur (Sudan). The combination of decades of drought, desertification and overpopulation are some of the causes of the conflict because the Baggara Arabs (nomadic Arabs) took their livestock further south in search of water, to land occupied mainly for the agriculture of the towns.[21].
A study published in the journal Science suggests that, due to climate change, South Africa could lose more than 30% of its main crop, maize, by 2030. In South Asia, losses of regional staples such as rice, millet and maize could reach 10%.[22][23].
The IPCC (2007:14) projected that it is very likely that in the dry areas of Latin America the production of some crops and livestock will decrease, with unfavorable consequences for obtaining food. In temperate zones, soybean crops would grow. Productivity is expected to fall by more than 30% during the century. The fish industry will also be greatly affected in many places.[24][25][26].
In the United States, increased temperature and precipitation may not have significant effects on the most important crops.[27] According to the IPCC (2007:14-15) it is expected that in the first decades of this century, moderate climate change will increase the production of crops that only receive precipitation by 5-20%. but with high variability between regions. The greatest challenge will be for crops that are close to the appropriate temperature range or those that depend on highly used water resources.
With medium probabilities, the IPCC projected that by mid-century, in East and Southeast Asia, crops would increase by 20%, while in Central and South Asia, they would decline by 30%. At a general level, the risk of hunger was projected to be very high in several developed countries. In South Asia, losses of commodities such as rice, millet and corn could reach 10%.[28].
The IPCC (2007:14) projected that there will be a high probability that climate change will reduce crop production in Southern Europe. In central and eastern Europe, forest productivity is expected to decline. In northern Europe, the initial effect of climate change will be to increase crop production.
Spain is a major world producer of cereals, vegetables, fruits and oil. In the last three decades, dryland cereals grown in Spain have advanced growth stages that develop in spring as a consequence of the effects of global change, which in the Peninsula have manifested themselves with an increase in average temperature and a slight decrease, but greater intensity, in rainfall. The most significant advance in their phenological stages has been recorded in wheat and oats, whose phases of appearance of the flag leaf and flowering have been advanced by an average of three and one day per year respectively. Phenological variations can have a great impact on the final crop production.[29] For its part, the phenology and flowering of the olive tree is also being seriously affected by global change.[30][31] Something that can have serious repercussions given that the flowering of the olive tree and crop production are closely related.[32][33] The advance in the activity of sap-sucking insects has also been reported by different farmers, such as aphids, red spider, St. Joseph's louse, etc. derived from the advance in the calendar of spring temperatures to the month of February. This has been reported especially in the Mediterranean area.
In Oceania, without future adaptation to climate change, the impacts on agriculture would be considerable.[34] By 2030, agriculture and forestry production would decline in southern and eastern Australia and some parts of eastern New Zealand. The initial benefits are projected to be larger rivers to the south and west.[34].
Brown reported for The Guardian newspaper in 2005 how climate change had affected agriculture in Iceland. The high temperatures made it possible to grow barley, something that had not been possible for 20 years. This warming occurred due to the change in ocean currents in the Caribbean, also affecting fishing.[35].
Anisimov et al. (2007:655) studied the climate of this region.[36] With a medium probability, they concluded that the benefits of a less severe climate would depend on local conditions. One of these benefits would be to increase opportunities for agriculture and forestry.
In a study, Mimura et al. (2007:689) concluded with a high probability that subsistence agriculture and commercial agriculture on small islands would be severely affected by climate change.[37]