Effects of climate change on agriculture

There are numerouseffects ofclimate changeon agriculture, many of which are making it harder for agricultural activities to provide globalfood security. Rising temperatures and changing weather patterns often result in lower crop yields due towater scarcitycaused bydrought,heat wavesandflooding.Theseeffects of climate changecan also increase the risk of several regions suffering simultaneouscrop failures. Currently this risk is regarded as rare but if these simultaneous crop failures did happen they would have significant consequences for the global food supply.Manypestsandplant diseasesare also expected to either become more prevalent or to spread to new regions. The world'slivestockare also expected to be affected by many of the same issues, from greaterheat stresstoanimal feedshortfalls and the spread ofparasitesandvector-borne diseases.
The increasedatmospheric CO2levelfrom human activities (mainly burning offossil fuels) causes aCO2fertilization effect. This effect offsets a small portion of the detrimental effects of climate change on agriculture. However, it comes at the expense of lower levels of essentialmicronutrientsin the crops.Furthermore, CO2fertilization has little effect onC4 cropslikemaize.On the coasts, some agricultural land is expected to be lost tosea level rise, whilemelting glacierscould result in lessirrigationwater being available.On the other hand, morearable landmay become available asfrozen landthaws. Other effects include erosion and changes insoil fertilityand the length of growing seasons. Also, bacteria likeSalmonellaandfungithat producemycotoxinsgrow faster as the climate warms. Their growth has negative effects onfood safety,food lossandprices.
There has been extensive research on the effects of climate change on individual crops, particularly on the fourstaple crops:corn(maize),rice,wheatandsoybeans. These crops are responsible for around two-thirds of all calories consumed by humans (both directly and indirectly as animal feed).The research investigates important uncertainties, for examplefuture population growth, which will increase global food demand for the foreseeable future.The future degree ofsoil erosionandgroundwater depletionare further uncertainties. On the other hand, a range of improvements to agricultural yields, collectively known as theGreen Revolution, has increased yields per unit of land area by between 250% and 300% since 1960. Some of that progress will likely continue.
The scientific consensus is that global food security will change relatively little in the near-term. 720 million to 811 million people were undernourished in 2021, with around 200,000 people being at acatastrophic levelof food insecurity.Climate change is expected to add an additional 8 to 80 million people who are at risk of hunger by 2050. The estimated range depends on the intensity of future warming and the effectiveness ofadaptation measures.Agricultural productivity growth will likely have improved food security for hundreds of millions of people by then.Predictions that reach further into the future (to 2100 and beyond) are rare. There is some concern about the effects on food security from moreextreme weatherevents in future.Nevertheless, at this stage there is no expectation of a widespread globalfaminedue to climate change within the 21st century.
Agriculture is sensitive to weather, and major events likeheatwavesordroughtsor heavy rains (also known as low and highprecipitationextremes) can cause substantial losses. For example,Australia's farmers are very likely to suffer losses during theEl Ninoweather conditions, while2003 European heat waveled to 13 billioneurosin uninsured agriculture losses.Climate change is known to increase the frequency and severity ofheatwaves, and to make precipitation less predictable and more prone to extremes, but sinceclimate change attributionis still a relatively new field, connecting specific weather events and the shortfalls they cause to climate change over natural variability is often difficult. Exceptions includeWest Africa, where the climate-induced intensification ofextreme weatherwas found to have already decreasedmilletyields by 10–20%, andsorghumyields 5–15%. Similarly, it was found that climate change had intensified drought conditions inSouthern Africain 2007, which elevatedfood pricesand caused "acute food insecurity" in the country ofLesotho. Agriculture in Southern Africa was also adversely affected by drought after climate change intensified the effects of2014–2016 El Niño event.
InEurope, between 1950 and 2019, heat extremes have become more frequent and also more likely to occur consecutively, while cold extremes have declined. At the same time,Northern Europeand much ofEastern Europewas found to experience extremeprecipitationmore often, while theMediterraneanbecame more affected bydrought.Similarly, the severity of heatwave and drought effects on European crop production was found to have tripled over a 50-year period – from losses of 2.2% during 1964–1990 to losses of 7.3% in 1991–2015.In the summer of 2018, heat waves probably linked to climate change greatly reduced average yield in many parts of the world, especially Europe. During the month of August, more crop failures resulted in a rise in globalfood prices.
On the other hand, floods, often linked to climate change, have also had notable adverse effects on agriculture in the recent years. In May 2019, floods shortenedcornplanting season in theMidwestern United States, lowering the projected yield from 15 billionbushelsto 14.2.During the2021 European floods, estimates pointed to severe damage to the agricultural sector of Belgium, one of the countries hardest hit by the floods, including long-term effects likesoil erosion.InChina, 2023 research found that extreme rainfall had cost the country about 8% of its rice output over the two preceding decades. This was considered comparable to losses caused by extreme heat over this period.
Changes in temperature and weather patterns will alter areas suitable for farming.The current prediction is that temperatures will increase and precipitation will decrease inaridandsemi-aridregions (Middle East,Africa,Australia,Southwest United States, andSouthern Europe).In addition, crop yields intropical regionswill be negatively affected by the projected moderate increase in temperature (1–2 °C) expected to occur during the first half of the century.During the second half of the century, further warming is projected to decreasecropyields in all regions includingCanadaand theNorthern United States.Manystaple cropsare extremely sensitive to heat and when temperatures rise over 36 °C (97 °F), soybean seedlings are killed and corn pollen loses its vitality.
Higher winter temperatures and more frost-free days in some regions can currently be disruptive, as they can causephenological mismatchbetween flowering time of plants and the activity ofpollinators, threatening their reproductive success.In the longer term, however, they would result in longergrowing seasons.For example, a 2014 study found that maize yields in theHeilongjiangregion of China increased by between 7 and 17% per decade as a result of rising temperatures.On the other hand, a year 2017meta-analysiscomparing data from four different methods of estimating effect of warming (two types of climate model,statistical regressionsandfield experimentswhere land around certain crops was warmed by a certain amount to compare them with the controls) concluded that on a global scale, warming alone has consistently negative effects on the yields of four most important crops, suggesting that any increases would be down toprecipitationchanges and theCO2 fertilization effect.
Bothdroughtsandfloodscontribute to decreases incrop yields. On average, climate change increases the overall amount ofwater contained in the atmosphereby 7% per every 1 °C (1.8 °F), thus increasingprecipitation.However, this increase in precipitation is not distributed evenly in space (atmospheric circulationpatterns already cause different areas to receive different amounts of rainfall) or time: heavy rainfall, with the potential to cause floods, becomes more frequent. This means that under the probable mid-rangeclimate change scenario,SSP2-4.5, precipitation events globally will become larger by 11.5%, yet the time between them will increase by an average of 5.1%. Under the highest-emission scenarioSSP5-8.5, there will be an 18.5% increase in size of events and 9.6% increase in the duration between them. At the same time, water losses by plants through evotranspiration will increase almost everywhere due to higher temperatures.While the CO2fertilization effect also reduces such losses by plants, it depends on the area's climate which effect will dominate. As such, the2020–2023 Horn of Africa droughthas been primarily attributed to the great increase in evotranspiration exacerbating the effect of persistent low rainfall, which would have been more manageable in the cooler preindustrial climate.
In total, this means thatdroughtshave been occurring more frequently on average because of climate change. Africa, southern Europe, the Middle East, most of the Americas, Australia, South and Southeast Asia are the parts of the globe where droughts are expected to become more frequent and intense in spite of the global increase in precipitation.Droughts disturbterrestrial precipitation, evaporation and soil moisture,and these effects can be aggravated bypopulation growthandurban expansionspurring on increased demand for water.The ultimate outcome iswater scarcity, which results in crop failures and the loss of pasture grazing land for livestock,exacerbating pre-existingpovertyindeveloping countriesand leading tomalnutritionand potentiallyfamine.
Irrigationof crops is able to reduce or even remove the effects on yields of lower rainfall and higher temperatures – through localized cooling.  However, using water resources for irrigation has downsides and is expensive.Further, some sources of irrigation water may become less reliable. This includes irrigation driven bywater runofffromglaciersduring the summer, as there has already been an observedretreat of glaciers since 1850, and it is expected to continue, depleting the glacial ice and reducing or outright eliminating runoff.In Asia, global warming of 1.5 °C (2.7 °F) will reduce the ice mass of Asia's high mountains by about 29–43%,:Approximately 2.4 billion people live in thedrainage basinof the Himalayan rivers:InIndiaalone, the riverGangesprovides water for drinking and farming for more than 500 million people.In theIndus Riverwatershed, these mountain water resources contribute to up to 60% of irrigation outside of the monsoon season, and an additional 11% of total crop production.SinceEffects of climate change on the water cycleare projected to substantially increase precipitation in all but the westernmost parts of the watershed, the loss of the glaciers is expected to be offset: however, agriculture in the region will become more reliable on monsoon than ever, andhydropowergeneration would become less predictable and reliable.
Elevated atmospheric carbon dioxide affects plants in a variety of ways. ElevatedCO2increases crop yields and growth through an increase in photosynthetic rate, and it also decreases water loss as a result ofstomatalclosing.
Changes in atmosphericcarbon dioxidemay reduce thenutritionalquality of some crops, with for instance wheat having less protein and less of some minerals.The nutritional quality ofC3 plants(e.g. wheat, oats, rice) is especially at risk: lower levels of protein as well as minerals (for example zinc and iron) are expected.Food crops could see a reduction ofprotein,ironandzinccontent in common food crops of 3 to 17%.This is the projected result of food grown under the expected atmospheric carbon-dioxide levels of 2050. Using data from theUN Food and Agriculture Organizationas well as other public sources, the authors analysed 225 different staple foods, such aswheat,rice,maize,vegetables, roots andfruits.
The effect of increased levels of atmospheric carbon dioxide on the nutritional quality of plants is not limited only to the above-mentioned crop categories and nutrients. A 2014meta-analysishas shown that crops and wild plants exposed to elevatedcarbon dioxidelevels at various latitudes have lower density of several minerals such as magnesium, iron, zinc, and potassium.
Studies usingFree-Air Concentration Enrichmenthave also shown that increases in CO2lead to decreased concentrations ofmicronutrientsin crop and non-crop plants with negative consequences for human nutrition,including decreased B vitamins in rice.This may have knock-on effects on other parts ofecosystemsas herbivores will need to eat more food to gain the same amount of protein.
Empirical evidence shows that increasing levels of CO2result in lower concentrations of many minerals in plant tissues. Doubling CO2levels results in an 8% decline, on average, in the concentration of minerals.Declines in magnesium, calcium, potassium, iron, zinc and other minerals in crops can worsen the quality of human nutrition. Researchers report that the CO2levels expected in the second half of the 21st century will likely reduce the levels of zinc, iron, and protein in wheat, rice, peas, and soybeans. Some two billion people live in countries where citizens receive more than 60 per cent of their zinc or iron from these types of crops. Deficiencies of these nutrients already cause an estimated loss of 63 million life-years annually.
Alongside a decrease in minerals, evidence shows that plants contain 6% more carbon, 15% less nitrogen, 9% less phosphorus, and 9% less sulfur at double CO2conditions. The increase in carbon is mostly attributed tocarbohydrateswithout a structural role in plants – the human-digestable, calorie-providing starch and simple sugars. The decrease in nitrogen translates directly into a decrease in the protein content. As a result, higher CO2not only reduce a plant's micronutrients, but also the quality of its macronutrient combination.
Anthropogenicmethane emissionshave a significant contribution to warming due to the highglobal warming potentialof methane. At the same time, methane also acts as a precursor tosurface ozone, which is a significantair pollutant. Its effects include loweringphysiological functionsand therefore the yield and quality of crops.Following methane levels, tropospheric ozone levels "increased substantially since the late 19th century",and according to a 2016 estimate, the four major crops (see later section) experienced yield losses of 5±1.5% relative to a no-climate change scenario due to ozone increases alone, which is nearly half of the negative effects caused by the other effects of climate change (10.9±3.2%), and cancels out most of the CO2fertilization effect (6.5±1.0%).
The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events.Erosionandsoil degradationis more likely to occur.Soil fertilitywould also be affected by global warming. Increased erosion in agricultural landscapes from anthropogenic factors can occur with losses of up to 22% of soil carbon in 50 years.
Climate change will also cause soils to warm. In turn, this could cause thesoil microbepopulation size to dramatically increase 40–150%. Warmer conditions would favour growth of certain bacteria species, shifting the bacterial community composition. Elevated carbon dioxide would increase the growth rates of plants and soil microbes, slowing the soil carbon cycle and favouringoligotrophs, which are slower-growing and more resource efficient thancopiotrophs.
Arise in the sea levelwould result in an agriculturalland loss, in particular in areas such asSouth East Asia.Erosion,submergence of shorelines,salinityof thewater tabledue to the increased sea levels, could mainly affect agriculture throughinundationoflow-lying lands. Low-lying areas such asBangladesh,IndiaandVietnamwill experience major loss of rice crop if sea levels rise as expected by the end of the century. Vietnam for example relies heavily on its southern tip, where theMekong Deltalies, for rice planting. A one-metre rise in sea level will cover several square kilometres ofrice paddiesin Vietnam.
Besides simply flooding agricultural land, sea level rise can also causesaltwater intrusioninto freshwaterwells, particularly if they are already below sea level. Once the concentration of saltwater exceeds 2–3%, the well becomes unusable. Notably, areas along an estimated 15% of the US coastline already have the majority of localgroundwaterbelow the sea level.
Climate change may increase the amount ofarable landby reducing the amount of frozen land. A 2005 study reports that temperature in Siberia has increased three-degree Celsius in average since 1960 (much more than the rest of the world).However, reports about the effect of global warming on Russian agricultureindicate conflicting probable effects: while they expect a northward extension of farmable lands,they also warn of possible productivity losses and increased risk of drought.
TheArcticregion is expected to benefit from increased opportunities for agriculture andforestry.
Climate change will alterpest,plant diseaseandweeddistributions, with potential to reduce crop yields, including ofstaple cropslikewheat,soybeans, and corn (maize).Warmer temperatures can increase themetabolic rateand number of breeding cycles ofinsectpopulations.Historically,cold temperatures at nightand in thewintermonths would kill offinsects,bacteriaandfungi. The warmer, wetter winters are promoting fungal plant diseases like wheat rusts (stripeandbrown/leaf) andsoybean rustto travel northward.The increasing incidence of flooding and heavy rains also promotes the growth of various other plant pests and diseases.
Climate change is expected to have a negative effect on many insects, greatly reducing theirspecies distributionand thus increasing theirrisk of going extinct.Around 9% of agricultural production is dependent in some way oninsect pollination,and somepollinatorspecies are also adversely affected, with wildbumblebeesknown to be particularly vulnerable to recent warming.
At the same time, insects are the most diverse animal taxa, and some species will benefit from the changes, including notable agricultural pests anddisease vectors.Insects that previously had only two breeding cycles per year could gain an additional cycle if warm growing seasons extend, causing a population boom. Temperate places and higherlatitudesare more likely to experience a dramatic change in insect populations:for instance, theMountain Pine Beetleepidemic inBritish Columbia,Canadahad killed millions of pine trees, partially because the winters were not cold enough to slow or kill the growing beetle larvae.Likewise,potato tuber mothandColorado potato beetleare predicted to spread into areas currently too cold for them.
Further,effects of climate change on the water cycleoften mean that both wet seasons and drought seasons will become more intense. Some insect species will breed more rapidly because they are better able to take advantage of such changes in conditions.This includes certain insect pests, such asaphidsandwhiteflies:similarly,locustswarms could also cause more damage as the result. A notable example was the2019–2022 locust infestationfocused onEast Africa, considered the worst of its kind in many decades.
Thefall armyworm,Spodoptera frugiperda, is a highly invasive plant pest, which can cause have massive damage to crops, especially maize. In the recent years, it has spread to countries insub-Saharan Africa, and this spread is linked to climate change. It is expected that these highly invasive crop pests will spread to other parts of the planet since they have a high capacity to adapt to different environments.
A changing climate may favour the more biologically diverseweedsover themonocropson many farms.Characteristics of weeds such as theirgenetic diversity,cross-breedingability, and fast-growth rates put them at an advantage in changing climates as these characteristics allow them toadaptreadily in comparison to most farm's uniform crops, and give them a biological advantage.
Weeds also undergo the same acceleration of cycles ascultivated crops, and would also benefit fromCO2fertilization. Since most weeds areC3 plants, they are likely to compete even more than now againstC4 cropssuch as corn.The increased CO2levels are also expected to increase the tolerance of weeds toherbicides, reducing their efficiency.However, this may be counteracted by increased temperatures elevating their effectiveness.
Currently, pathogens result in losses of 10–16% of the global harvest and this level is likely to rise as plants are at an ever-increasing risk of exposure to pests andpathogens.Research has shown that climate change may alter the developmental stages ofplant pathogensthat can affect crops. This includes several pathogens associated with potato blackleg disease (e.g.Dickeya), as they grow and reproduce faster at higher temperatures.The warming is also expected to elevatefood safetyissues and food spoilage caused bymycotoxin-producing fungi, and bacteria such asSalmonella.
Climate change would cause an increase in rainfall in some areas, which would lead to an increase of atmospheric humidity and the duration of thewet seasons. Combined with higher temperatures, these conditions could favour the development offungaldiseases, such aslate blight,or bacterial infections such asRalstonia solanacearum, which may also be able to spread more easily throughflash flooding.
Climate change has the capability of altering pathogen and host interactions, specifically the rates of pathogen infection and the resistance of the host plant.Also affected by plant disease are the economic costs associated with growing different plants that might yield less profit as well as treating and managing already diseased crops.For instance,soybean rustis a vicious plant pathogen that can kill off entire fields in a matter of days, devastating farmers and costing billions in agricultural losses.Change in weather patterns and temperature due to climate change leads to dispersal ofplant pathogensas hosts migrate to areas with more favourable conditions. This increases crop losses due to diseases.For instance,aphidsact as vectors for many potatovirusesand will be able to spread further due to increased temperatures.
According to theIPCC Sixth Assessment Reportfrom 2022, there ishigh confidencethat in and of itself, climate change to date has left primarily negative effects on bothcrop yieldsand quality of produce, although there has been some regional variation:more negative effects have been observed for some crops in low-latitudes (maize and wheat), while positive effects of climate change have been observed in some crops in high-latitudes (maize, wheat, andsugar beets).I.e. during the period 1981 to 2008, global warming has had negative effects on wheat yield in especially tropical regions, with decreases in average global yields by 5.5%.A study in 2019 tracked ~20,000 political units globally for 10 crops (maize,rice,wheat,soybean,barley,cassava,oil palm,rapeseed,sorghumandsugarcane), providing more detail on the spatial resolution and a larger number of crops than previously studied.It found that crop yields across Europe, sub-Saharan Africa, and Australia had in general decreased because of climate change (compared to the baseline value of 2004–2008 average data), though exceptions are present. The effect of global climate change on yields of different crops from climate trends ranged from −13.4% (oil palm) to 3.5% (soybean). The study also showed that effects are generally positive in Latin America. Effects in Asia and Northern and Central America are mixed.
While theGreen Revolutionhad ensured the growth of overall crop production per land area of 250% to 300% since the 1960,with around 44% attributed to newer crop varieties alone,it is believed this growth would have been even greater without the counteracting role of climate change on major crop yields over the same period. Between 1961 and 2021, global agricultural productivity could have been 21% greater than it actually was, if it did not have to contend with climate change. Such shortfalls would have affectedfood securityofvulnerable populationsthe most:a study in 2019 showed that climate change has already increased the risk of food insecurity in many food insecure countries.Even indeveloped countriessuch asAustralia, extreme weather associated with climate change has been found to cause a wide range of cascading spillovers throughsupply chaindisruption, in addition to its primary effect on fruit, vegetable, and livestock sectors and the rural communities reliant on them.
Between 1961 and 1985,cerealproduction more than doubled indeveloping nations, largely due to the development of irrigation, fertilizer, and seed varieties.Even in the absence of further scientific/technological developments, many of the existing advancements have not been evenly distributed, and their spread from thedeveloped worldto thedeveloping worldis expected to drive some improvements on its own. Further,agricultural expansionhas slowed down in the recent years, but this trend is widely expected to reverse in the future in order to maintain the global food supply under all but the most optimisticclimate change scenariosconsistent with theParis Agreement.
In 2007, theIPCC Fourth Assessment Reporthad suggested that global production potential would increase up to around 3 °C (5.4 °F) of globally averaged warming, as productivity increases for cereals in high latitudes would outweigh decreases in the low latitudes and global aggregate yields of rain-fed agriculture would increase by 5–20% in the first half of the 21st century. Warming exceeding this level would very likely see global declines in yields.Since then, subsequent reports had been more negative on the global production potential.
TheUS National Research Councilassessed the literature on the effects of climate change on crop yields in 2011,and provided central estimates for key crops.A meta-analysis in 2014 revealed consensus that yield is expected to decrease in the second half of the century, and with greater effect in tropical than temperate regions.
There is a large number of agriculturalcrops, but not all of them are equally important. Most climate change assessments focus on "four major crops" –maize(corn),rice,wheatandsoybeans– which are consumed directly and indirectly, asanimal feed(the main purpose of soybeans). The threecerealsare collectively responsible for half of the total humancalorieintake,and together with soybeans, they account for two thirds.Different methods have been used to project future yields of these crops, and by 2019, the consensus was that warming would lead to aggregate declines of the four. Maize andsoybeanwould decrease with any warming, whereas rice and wheat production might peak at 3 °C (5.4 °F) of warming.
In 2021, a paper which used an ensemble of 21climate modelsestimated that under the most intenseclimate change scenarioused at the time,RCP8.5, global yields of these four crops would decline by between 3–12% around 2050 and by 11–25% by the year 2100. The losses were concentrated in what are currently the major agricultural producers and exporters. For instance, even by 2050, some agricultural areas ofAustralia,Brazil,South Africa,Southeast China,Southern Europeand theUnited Stateswould suffer production losses of mostly maize and soybeans exceeding 25%.A similar finding - that some major "breadbaskets" would begin to see unequivocal effects of climate change, both positive and negative, before the year 2040 - had been established in another study from the same year.Since it represents the worst-case scenario of continually increasing emissions with no efforts to reduce them, RCP8.5 is often considered unrealistic,and a less intense RCP4.5 scenario (which still leads to nearly 3 °C (5.4 °F) by century's end, far in excess of theParis Agreementgoals) is now usually considered a better match for the current trajectory.
Out of the four crops, maize is considered the most vulnerable to warming, with one meta-analysis concluding that every 1 °C (1.8 °F) of global warming reduces maize yields by 7.4%.
It is also aC4 carbon fixationplant, meaning that it experiences little benefit from the increased CO2levels.When the results from modelling experiments comparing the combined output of latestearth system modelsand dedicated agricultural crop models were published in 2021, the most notable new finding was the substantial reduction in projected global yields of maize. While the previous generation suggested that under the low-warming scenario, maize productivity would increase by around 5% by the end of the century, the latest had shown a reduction of 6% under the equivalent scenario,SSP1-2.6. Under the high-emission SSP5-8.5, there was a global decline of 24% by 2100, as opposed to the earlier suggestion of a 1% increase.
Studies indicate that on their own, temperature changes reduce global rice yields by 3.2% for every 1 °C (1.8 °F) of global warming.Projections become more complicated once the changes in precipitation, CO2fertilization effect and other factors need to be taken into account: for instance, climate effects on rice growth inEast Asiahad been a net positive so far,although 2023 research suggested that by the end of the century,Chinacould lose up to 8% of its rice yield due to increases in extreme rainfall events alone.As of 2021, global projections of rice yields from the most advanced climate and agricultural models were less consistent than they were for wheat and maize, and less able to identify a clear statistically significant trend.
Climate change effects onrainfedwheatwill vary depending on the region and local climatic conditions. Studies inIransurrounding changes in temperature and rainfall are representative for several different parts of the world since there exists a wide range of climatic conditions. They range from temperate to hot-arid to cold semi-arid. Scenarios based on increasing temperature by up to 2.5 °C (4.5 °F) and rainfall decreases by up to 25% show wheat grain yield losses can be significant. The losses can be as much as 45% intemperate areasand over 50% in hot-arid areas. But in cold semi-arid areas yields can be increased somewhat (about 15%). Adaptation strategies with the most promise center around dates for seed planting. Late planting in November to January can have significant positive effects on yields due to the seasonality of rainfall.However, those experiments did not consider the effects of CO2increases.
Globally, temperature changes alone are expected to reduce annual wheat yield by 6% for every 1 °C (1.8 °F) of global warming.However, other factors such as precipitation and the CO2fertilization effect benefit wheat yields far more. In November 2021, the results from modelling experiments comparing the combined output of latestearth system modelsand dedicated agricultural crop models were published. While it projected a consistent decrease in future global yields of maize, particularly under greater warming, it found the opposite for wheat yields. When the previous generation of models suggested a 9% increase in global wheat yields by 2100 under the high-emission scenario, the updated results indicate that under its highest-warming SSP5-8.5 scenario, they would increase by 18%.
Studies have shown that when CO2levels rise,soybeanleaves are less nutritious; therefore plant-eating beetles have to eat more to get their requirednutrients.In addition, soybeans are less capable of defending themselves against thepredatory insectsunder high CO2. The CO2diminishes the plant'sjasmonic acidproduction, an insect-killing poison that is excreted when the plant senses it is being attacked. Without this protection, beetles are able to eat the soybean leaves freely, resulting in a lower crop yield.This is not a problem unique to soybeans, and many plant species' defence mechanisms are impaired in a high CO2environment.
Studies indicate that on their own, temperature changes reduce global soybean yields by 3.1% for every 1 °C (1.8 °F) of global warming.These projections become more complicated once the changes in precipitation, CO2fertilization effect and other factors need to be taken into account: as of 2021, global projections of soybean yields from the most advanced climate and agricultural models were less able to establish a strong trend when compared to the projections for maize and wheat.
Climate change induced by increasinggreenhouse gasesis likely to differ across crops and countries.
Milletandsorghumare not as widely consumed as the four major crops, but they are crucialstaplesin manyAfricancountries. A paper published in the year 2022 found that under the highest-warmingSSP5-8.5scenario, changes in temperature andsoil moisturewould reduce the aggregate yields of millet, sorghum, maize and soybeans by between 9% and 32%, depending on the model. Notably, this was a less pessimistic result than in the earlier models, which the authors attributed to simulating soil moisture directly, rather than attempting to indirectly account for it by trackingprecipitationchanges caused byeffects of climate change on the water cycle.
Climate change induced drought stress in Africa will likely lead to a reduction in the nutritional quality of the common bean.This would primarily impact populations in poorer countries less able to compensate by eating more food, more varied diets, or possibly taking supplements.
As well as affecting potatoes directly, climate change will also affect the distributions and populations of many potato diseases and pests. For instance,late blightis predicted to become a greater threat in some areas (e.g. inFinland) and become a lesser threat in others (e.g. in theUnited KingdomAltogether, one 2003 estimate suggests that future (2040–2069) worldwide potato yield would be 18–32% lower than it was at the time, driven by declines in hotter areas like Sub-Saharan Africa,unless farmers and potato cultivars can adapt to the new environment.
Scientific understanding of how climate change would affect globalfood securityhas evolved over time. The latestIPCC Sixth Assessment Reportin 2022 suggested that by 2050, the number of people at risk of hunger will increase under all scenarios by between 8 and 80 million people, with nearly all of them inSub-Saharan Africa,South AsiaandCentral America. However, this comparison was done relative to a world where no climate change had occurred, and so it does not rule out the possibility of an overall reduction in hunger risk when compared to present-day conditions.
The earlierSpecial Report on Climate Change and Landsuggested that under a relatively high emission scenario (RCP6.0), cereals may become 1–29% more expensive in 2050 depending on the socioeconomic pathway.Compared to a scenario where climate change is absent, this would put between 1–181 million people with low income at risk of hunger.
It is difficult to project the effect of climate change on utilization (protecting food against spoilage, being healthy enough to absorb nutrients, etc.). In 2016, a modelling study suggested that by mid-century, the most intense climate change scenario would reduce per capita global food availability by 3.2%, with a 0.7% decrease inred meatconsumption and a 4% decrease infruitandvegetableconsumption. According to its numbers, 529,000 people would die between 2010 and 2050 as the result, primarily inSouth AsiaandEast Asia: two-thirds of those deaths would be caused by the lack ofmicronutrientsfrom reducedfruitandvegetablesupply, rather than outright starvation. Acting to slow climate change would reduce these projections by up to 71%.Food pricesare also expected to become more volatile.
As of 2017, around 821 million people had suffered from hunger. This was equivalent to about 11% of the world population: regionally, this included 23.2% ofsub-Saharan Africa, 16.5% of theCaribbeanand 14.8% ofSouth Asia.In 2021, 720 million to 811 million people were considered undernourished in 2021 (of whom 200,000, 32.3 million and 112.3 million people were at a "catastrophic", "emergency" and "crisis" levels of food insecurity, respectively).
In 2020, research suggested that the baseline projected level of socioeconomic development (Shared Socioeconomic Pathway 2) would reduce this number to 122 million globally by 2050, even as the population grows to reach 9.2 billion. The effect of climate change would at most increase this 2050 figure by around 80 million, and the negative effect could be reduced to 20 million through enabling easier food trade with measures such as eliminatingtariffs.
In 2021, ameta-analysisof 57 studies on food security was more pessimistic, suggesting that the year 2050 population at risk of hunger would be around 500 million under SSP2. Some variations ofShared Socioeconomic Pathwayswith high climate change and a lack of equitableglobal developmentinstead resulted in an outright increase of global hunger by up to 30% from its 2010 levels.
For the earlierIPCC Fourth Assessment Reportin 2007, the analysis of four mainSRESpathways had shown withmedium confidence(about 50% certainty)) that trends ofsocialandeconomic developmentin three of them (A1, B1, B2) would see the number of undernourished people decline to 100–130 million people by the year 2080, while trends in A2 projected 770 million undernourished – similar to the contemporary (early 21st century) figures of ~700 million people. Once the effect of climate change implied by those scenarios was taken into account, A1, B1 and B2 scenarios would see 100–380 million undernourished by 2080 (still a major decline inhungerfrom 2006 levels), and A2 would see 740–1,300 million, although there was onlylow(20% certainty) tomediumcertainty in these figures.Sub-Saharan Africawould likely overtakeAsiaas the world's most food-insecure region, primarily due to differing socioeconomic trends.
Some scientists consider the aforementioned projections of crop yields and food security of limited use, because in their view, they primarily model climate change as a change in mean climate state, and are not as well-equipped to consider climatic extremes. For instance, a paper published in 2021 had also attempted to calculate the number of people facing hunger in 2050 – but now on the assumption that a climate event with a 1% (i.e. once in 100 years) likelihood of occurring in thenewclimate (meaning it would have been effectively impossible in the present climate) were to impact that year. It estimated that such an event would increase the baseline number by 11–33% even in the low-emission scenario, and by 20–36% in the high-emission one. If such an event were to affect more vulnerable regions likeSouth Asia, then they would have required triple their 2021 level of known food reserves to absorb the blow.
Notably, other papers show that simulating recent historical extreme events in climate models, such as the2003 European heatwave, typically results in lower effects than what had been observed in the real world, indicating that the effects of future extreme events are also likely to be underestimated.
The difference between climatic mean and extremes may be particularly important for determining areas where agriculture may stop being viable. In 2021, a research team aimed to extendclimate modelprojections of mean changes in temperature andthe water cycleto the year 2500. They suggested that under the second-strongest warming scenario RCP6.0, land area capable of supporting four major temperate crops (maize, potato, soybean and wheat) would become about 11% smaller by 2100 and 18.3% smaller by 2500, while for major tropical crops (cassava, rice,sweet potato,sorghum,taro, andyam), it would decline by only 2.3% around 2100, yet by around 15% by 2500. Under the low-emission scenario RCP2.6, changes are much smaller, with around 3% decline in suitable land area for temperate crops by 2500 and an equivalent gain for tropical crops by then.
Yet, another paper from 2021 suggested that by 2100, under the high-emission SSP5-8.5, 31% and 34% of the current crop and livestock production would leave what the authors have defined as a "safe climatic space": that is, those areas (most ofSouth Asiaand theMiddle East, as well as parts ofsub-Saharan AfricaandCentral America) would experience very rapid shift inHoldridge life zones(HLZ) and associated weather, while also being low in social resilience. Notably, a similar fraction of global crop and livestock production would also experience a large change in HLZ, but in more developed areas which would have better chances of adapting. In contrast, under the low-emissions SSP1-2.6, 5% and 8% of crop and livestock production would leave what is defined as the safe climatic space.
Also in 2021, it was suggested that the high-emission scenario would result in a 4.5-fold increase in the probability of breadbasket failures (defined as a yield loss of 10% or more) by 2030, which could then increase 25 times by 2050.This corresponds to reaching 1.5 °C (2.7 °F) and 2 °C (3.6 °F) thresholds under that scenario: earlier research suggested that for maize, this would increase risks formultiple simultaneous breadbasket failures(yield loss of 10% or more) from 6% under the late-20th century climate to 40% and 54%, respectively.
Some countries are particularly dependent on imports from certain exporters, meaning that a crop failure in those countries would hit them disproportionately. I.e. a ban on export of staple crops fromRussia,Thailandand theUnited Statesalone would place around 200 million people (90% from Sub-Saharan Africa) at risk of starvation.
Additionally, there is the issue of representing synchronization - where extreme climate events happen to strike multiple important producer regions around the same time. It was estimated that if hypothetically, every region with a synchronized growing season were to experience crop failure at the same time, it would cause losses of four major crops between 17% and 34%.More realistically, analysis of historic data suggested that there have already been synchronized climate events associated with up to 20% yield losses.
According to a 2016 estimate, if global maize, rice and wheat exports declined by 10%, 55 million people in 58 poor countries lose at least 5% of their food supply.Further, two specificRossby wavepattern are known to induce simultaneous heat extremes in eitherEastern Asia,Eastern Europeand Central North America, or inWestern Asia,Western Europeand Western Central North America, respectively. These heat extremes have already been shown to cause 3–4% declines in crop yield across the affected regions:yet, concerningly, climate models overestimate the effects of such historic events in North America and underestimate them elsewhere, simulating effectively no net yield loss.
Asextreme weather eventsbecome more common and more intense, floods and droughts can destroy crops and eliminate food supply, while disrupting agricultural activities and rendering workers jobless.With more costs to the farmer, some will no longer find it financially feasible to farm: i.e. some farmers may choose to permanently leave drought-affected areas.Agricultureemploys the majority of the population in most low-income countries and increased costs can result in worker layoffs or pay cuts.Other farmers will respond by raising theirfood prices; a cost that is directly passed on to the consumer and affects the affordability of food. Some farms do not sell their produce but instead feed a family or community; without that food, people will not have enough to eat. This results in decreased production, increased food prices, and potential starvation in parts of the world.The agriculture industry inIndiamakes up 52% of their employment and theCanadian Prairiessupply 51% of Canadian agriculture; any changes in the production of food crops from these areas could have profound effects on theeconomy.
Notably, one estimate suggests that a warming of 3 °C (5.4 °F) relative to late 20th century (i.e. closer to 4 °C (7.2 °F) when compared to preindustrial temperatures – a level associated with the SSP5-8.5 scenario) would causelabour capacityinSub-Saharan AfricaandSoutheast Asiato decline by 30 to 50%, as the number of days when outdoor workers experienceheat stressincreases: up to 250 days the worst-affected parts of these two continents and ofCentralandSouth America. This could then increase crop prices by around 5%.
Similarly,North China Plainis also expected to be highly affected, in part due to the region's extensiveirrigationnetworks resulting in unusually moist air. In scenarios without aggressiveaction to stop climate change, some heatwaves could become extreme enough to cause mass mortality in outdoor labourers, although they will remain relatively uncommon (up to around once per decade starting from 2l00 under the most extreme scenario).
Further, the role of climate change in undernutrition and micronutrient deficiencies can be calculated as the loss of "years of full health".One estimate presented in 2016 suggests that under the scenario of strong warming and low adaptation due to high global conflict and rivalry, such losses may take up 0.4% of the globalGDPand 4% of the GDP in India and theSouth Asianregion by the year 2100.
There are fewer projections looking beyond 2050. In general, even as climate change would cause increasingly severe effects on food production, most scientists do not anticipate it to result in mass human mortality within this century.This is in part because the studies also anticipate at least some continuation of the ongoing agricultural improvements, yet also because ofagricultural expansion. For instance, a 2013 paper estimated that if the high warming ofRCP 8.5scenario was not alleviated by CO2fertilization effect, it would reduce aggregate yields by 17% by the year 2050: yet, it anticipated that this would be mostly offset through an 11% increase incroplandarea.
Similarly, one of the assumptions ofShared Socioeconomic Pathwaysis a significant increase in land allocated to agriculture (and a corresponding decrease inforestand "other natural land" area) in every pathway besides the SSP1 (officially subtitled "Sustainability" or "Taking the Green Road"), where the inverse occurs – and which has both the lowest level of future warming and the lowest projectedpopulation growth.
ForEastandSoutheast Asia, an estimate in 2007 stated thatcrop yieldscould increase up to 20% by the mid-21st century.InCentraland South Asia, projections suggested that yields might decrease by up to 30%, over the same time period. Taken together, the risk of hunger was projected to remain very high in several developing countries.
Different Asian Countries have various effects from climate change.China, for example, benefits from a 1.5 °C (2.7 °F) temperature increase scenario accompanying with carbon fertilization and leading to a 3% gain of US$18 billion per year; however,Indiawill face two thirds of the continent's aggregate losses on agriculture because its high corp net revenue suffers from the high spring temperature.In theIndo-Gangetic plainof India, heat stress and water availability are predicted to have significant negative effects on yield of wheat.Direct effects of increased mean and maximum temperatures is predicted to reduce wheat yields by up to 10%. The effect of reduced availability of water for irrigation is more significant, running at yield losses up to 35%.
Due to climate change,livestockproduction will be decreased inBangladeshby diseases, scarcity of forage, heat stress and breeding strategies.
Without further adaptation to climate change, projected effects would likely be substantial. By 2030, production from agriculture andforestrywas projected to decline over much of southern and eastern Australia, and over parts of eastern New Zealand.In New Zealand, initial benefits were projected close to major rivers and in western and southern areas.
ForSouthern Europe, it was predicted in 2007 that climate change would reduce crop productivity.InCentralandEastern Europe, forest productivity was expected to decline. InNorthern Europe, the initial effect of climate change was projected to increase crop yields. The 2019European Environment Agencyreport "Climate change adaptation in the agricultural sector in Europe" again confirmed this. According to this 2019 report, projections indicate that yields of non-irrigated crops like wheat, corn and sugar beet would decrease in southern Europe by up to 50% by 2050 (under a high-end emission scenario). This could result in a substantial decrease in farm income by that date. Also farmland values are projected to decrease in parts of southern Europe by more than 80% by 2100, which could result in land abandonment. The trade patterns are also said to be affected, in turn affecting agricultural income. Also, increased food demand worldwide could exert pressure on food prices in the coming decades.InUkraine, where temperatures are increasing throughout the year and precipitation is predicted to increase,winter wheatyields (wheat sown in winter) could increase by 20–40% in the north and northwestern regions by 2050, as compared to 2010.
The major agricultural products ofLatin Americaincludelivestockand grains; such as maize, wheat, soybeans, and rice.Increased temperatures and altered hydrological cycles are predicted to translate to shorter growing seasons, overall reduced biomass production, and lower grain yields.Brazil,MexicoandArgentinaalone contribute 70-90% of the total agricultural production in Latin America.In these and other dry regions, maize production is expected to decrease.A study summarising a number of impact studies of climate change on agriculture in Latin America indicated that wheat is expected to decrease in Brazil, Argentina andUruguay.Livestock, which is the main agricultural product for parts of Argentina, Uruguay, southern Brazil,Venezuela, andColombiais likely to be reduced.Variability in the degree of production decrease among different regions of Latin America is likely.For example, one 2003 study that estimated future maize production in Latin America predicted that by 2055 maize in eastern Brazil will have moderate changes while Venezuela is expected to have drastic decreases.
Increased rainfall variability has been one of the most devastating consequences of climate change in Central America and Mexico. From 2009 to 2019, the region saw years of heavy rainfall in between years of below average rainfall.The spring rains of May and June have been particularly erratic, posing issues for farmers plant their maize crops at the onset of the spring rains. Most subsistence farmers in the region have no irrigation and thus depend on the rains for their crops to grow. In Mexico, only 21% of farms are irrigated, leaving the remaining 79% dependent on rainfall.
Suggested potential adaptation strategies to mitigate the effects of global warming on agriculture in Latin America include using plant breeding technologies and installing irrigation infrastructure.
Droughts are becoming more frequent and intense in arid andsemiaridwestern North America as temperatures have been rising, advancing the timing and magnitude of spring snow melt floods and reducing river flow volume in summer.Direct effects of climate change include increased heat and water stress, altered cropphenology, and disrupted symbiotic interactions. These effects may be exacerbated by climate changes in river flow, and the combined effects are likely to reduce the abundance of native trees in favour of non-nativeherbaceousand drought-tolerant competitors, reduce the habitat quality for many native animals, and slow litter decomposition andnutrientcycling. Climate change effects on human water demand and irrigation may intensify these effects.
InCanada, notable increases are predicted for spring-sown wheat.
Climate change adaptation measures may reduce the risk of negative effects on agriculture from climate change. Adaptation can occur through changes in management practices, agricultural innovation, institutional changes, andclimate-smart agriculture.To create asustainable food system, these measures are considered as essential as changes needed to reduce global warming in general.
Agricultural innovation is essential to addressing the potential issues of climate change. This includes better management of soil, water-saving technology, matching crops to environments, introducing different crop varieties, crop rotations, appropriatefertilizationuse, and supporting community-based adaptation strategies.On a government and global level, research and investments intoagricultural productivityandinfrastructuremust be done to get a better picture of the issues involved and the best methods to address them.Government policiesand programs must provide environmentally sensitive governmentsubsidies, educational campaigns, and economic incentives as well as funds,insurance, and safety nets for vulnerable populations.In addition, providingearly warning systems, and accurateweather forecaststo poor or remote areas will allow for better preparation.