Climate change and agriculture

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Climate change and agriculture are interrelated processes, both of which take place on a global scale.[1] Global warming is projected to have significant impacts on conditions affecting agriculture, including temperature, precipitation and glacial run-off. These conditions determine the carrying capacity of the biosphere to produce enough food for the human population and domesticated animals. Rising carbon dioxide levels would also have effects, both detrimental and beneficial, on crop yields. The overall effect of climate change on agriculture will depend on the balance of these effects. Assessment of the effects of global climate changes on agriculture might help to properly anticipate and adapt farming to maximize agricultural production.

At the same time, agriculture has been shown to produce significant effects on climate change, primarily through the production and release of greenhouse gases such as carbon dioxide, methane, and nitrous oxide, but also by altering the earth's land cover, which can change its ability to absorb or reflect heat and light, thus contributing to radiative forcing. Land use change such as deforestation and desertification, together with use of fossil fuels, are the major anthropogenic sources of carbon dioxide; agriculture itself is the major contributor to increasing methane and nitrous oxide concentrations in earth's atmosphere.[2]

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[edit] Impact of climate change on agriculture

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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. 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 suggest 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%".[3][4]

The 2001 IPCC Third Assessment Report 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.

[edit] Shortage in grain production

Crops such as these sunflowers can be affected by severe drought conditions in Australia.
Crops such as these sunflowers can be affected by severe drought conditions in Australia.[5]

Between 1996 and 2003, grain production has stabilized slightly over 1800 millions of tons. In 2000, 2001, 2002 and 2003, grain stocks have been dropping, resulting in a global grain harvest that was short of consumption by 93 millions of tons in 2003.

The earth's average temperature has been rising since the late 1970s, with nine of the 10 warmest years on record occurring since 1995[6]. In 2002, India and the United States suffered sharp harvest reductions because of record temperatures and drought. In 2003 Europe suffered very low rainfall throughout spring and summer, and a record level of heat damaged most crops from the United Kingdom and France in the Western Europe through Ukraine in the East. Bread prices have been rising in several countries in the region. (see w:fr:canicule 2003).

[edit] Poverty impacts

Researchers at the Overseas Development Institute (ODI) have investigated the potential impacts climate change could have on agriculture, and how this would affect attempts at alleviating poverty in the developing world. They argued that the effects from moderate climate change are likely to be mixed for developing countries. However, the vulnerability of the poor in developing countries to short term impacts from climate change, notably the increased frequency and severity of adverse weather events is likely to have a negative impact. This, they say, should be taken into account when defining agricultural policy.[7]

[edit] Crop development models

Models for climate behavior are frequently inconclusive. In order to further study effects of global warming on agriculture, other types of models, such as crop development models, yield prediction, quantities of water or fertilizer consumed, can be used. Such models condense the knowledge accumulated of the climate, soil, and effects observed of the results of various agricultural practices. They thus could make it possible to test strategies of adaptation to modifications of the environment.

Because these models are necessarily simplifying natural conditions (often based on the assumption that weeds, disease and insect pests are controlled), it is not clear whether the results they give will have an in-field reality. However, some results are partly validated with an increasing number of experimental results.

Other models, such as insect and disease development models based on climate projections are also used (for example simulation of aphid reproduction or septoria (cereal fungal disease) development).

Scenarios are used in order to estimate climate changes effects on crop development and yield. Each scenario is defined as a set of meteorological variables, based on generally accepted projections. For example, many models are running simulations based on doubled carbon dioxide projections, temperatures raise ranging from 1°C up to 5°C, and with rainfall levels an increase or decrease of 20%. Other parameters may include humidity, wind, and solar activity. Scenarios of crop models are testing farm-level adaptation, such as sowing date shift, climate adapted species (vernalisation need, heat and cold resistance), irrigation and fertilizer adaptation, resistance to disease. Most developed models are about wheat, maize, rice and soybean.

[edit] Temperature potential effect on growing period

Duration of crop growth cycles are above all, related to temperature. An increase in temperature will speed up development. In the case of an annual crop, the duration between sowing and harvesting will shorten (for example, the duration in order to harvest corn could shorten between one and four weeks). The shortening of such a cycle could have an adverse effect on productivity because senescence would occur sooner.

[edit] Potential effect of atmospheric carbon dioxide on yield

Carbon dioxide is essential to plant growth. Rising CO2 concentration in the atmosphere can have both positive and negative consequences.

Increased CO2 is expected to have positive physiological effects by increasing the rate of photosynthesis. Currently, the amount of carbon dioxide in the atmosphere is 380 parts per million. In comparison, the amount of oxygen is 210,000 ppm. This means that often plants may be starved of carbon dioxide, being outnumbered by the photosynthetic pollutant oxygen. The effects of an increase in carbon dioxide would be higher on C3 crops (such as wheat) than on C4 crops (such as maize), because the former is more susceptible to carbon dioxide shortage. Under optimum conditions of temperature and humidity, the yield increase could reach 36%, if the levels of carbon dioxide are doubled.[citation needed]

However, other studies also show a change in harvest quality. The growth improvement in C3 plants could favor vegetative biomass on grain biomass; thus leading to a decrease in grain production yield.

Further, few studies have looked at the impact of elevated carbon dioxide concentrations on whole farming systems. Most models study the relationship between CO2 and productivity in isolation from other factors associated with climate change, such as an increased frequency of extreme weather events, seasonal shifts, and so on. Moreover, it is reasonable to expect that weed productivity will increase in parallel with that of crop and pasture plants; potentially raising the cost of defensive expenditures like herbicides.

In 2005, the Royal Society in London concluded that the purported benefits of CO2 fertilization are “likely to be far lower than previously estimated” when factors such as increasing ground-level ozone are taken into account." [8]

[edit] Effect on quality

According to the IPCC's TAR, "The importance of climate change impacts on grain and forage quality emerges from new research. For rice, the amylose content of the grain--a major determinant of cooking quality--is increased under elevated CO2" (Conroy et al., 1994). Cooked rice grain from plants grown in high-CO2 environments would be firmer than that from today's plants. However, concentrations of iron and zinc, which are important for human nutrition, would be lower (Seneweera and Conroy, 1997). Moreover, the protein content of the grain decreases under combined increases of temperature and CO2 (Ziska et al., 1997)."[9]

Studies have shown that higher CO2 levels lead to reduced plant uptake of nitrogen (and a smaller number showing the same for trace elements such as zinc) resulting in crops with lower nutritional value.[10][11] This would primarily impact on populations in poorer countries less able to compensate by eating more food, more varied diets, or possibly taking supplements.

Reduced nitrogen content in grazing plants has also been shown to reduce animal productivity in sheep, which depend on microbes in their gut to digest plants, which in turn depend on nitrogen intake.[12]

[edit] Agricultural surfaces and climate changes

Climate change is likely to increase the amount of arable land in high-lattitude region by reduction of the amount of frozen lands. A 2005 study reports that temperature in siberia has increased three degree celcius in average since 1960 (much more than the rest of the world).[13] However, reports about the impact of global warming on russian agriculture[14] indicate conflicting probable effects : while they expect an northward extension of farmable lands,[15] they also warn of possible productivity losses and increased risk of drought.[16]

Sea levels are expected to get up to one meter higher by 2100, though this projection is disputed. A rise in the sea level would result in an agricultural land loss, in particular in areas such as South East Asia. Erosion, submergence of shorelines, salinity of the water table due to the increased sea levels, could mainly affect agriculture through inundation of low-lying lands.

[edit] Erosion and fertility

With global warming, soil degradation is more likely to occur, and soil fertility would probably be affected by global warming. However, because the ratio of carbon to nitrogen is a constant, a doubling of carbon is likely to imply a higher storage of nitrogen in soils as nitrates, thus providing higher fertilizing elements for plants, providing better yields. The average needs for nitrogen could decrease, and give the opportunity of changing often costly fertilisation strategies.

Due to the extremes of climate that would result, the increase in precipitations would probably result in greater risks of erosion, whilst at the same time providing soil with better hydration, according to the intensity of the rain. The possible evolution of the organic matter in the soil is a highly contested issue: while the increase in the temperature would induce a greater rate in the production of minerals, lessening the soil organic matter content, the atmospheric CO2 concentration would tend to increase it.

[edit] Potential effects of global climate change on pests, diseases and weeds

A very important point to consider is that weeds would undergo the same acceleration of cycle as cultivated crops, and would also benefit from carbonaceous fertilization. Since most weeds are C3 plants, they are likely to compete even more than now against C4 crops such as corn. However, on the other hand, some results make it possible to think that weedkillers could gain in effectiveness with the temperature increase.[citation needed]

Global warming would cause an increase in rainfall in some areas, which would lead to an increase of atmospheric humidity and the duration of the wet seasons. Combined with higher temperatures, these could favor the development of fungal diseases. Similarly, because of higher temperatures and humidity, there could be an increased pressure from insects and disease vectors.

[edit] Glacier retreat and disappearance

The continued retreat of glaciers will have a number of different quantitative impacts. In areas that are heavily dependent on water runoff from glaciers that melt during the warmer summer months, a continuation of the current retreat will eventually deplete the glacial ice and substantially reduce or eliminate runoff. A reduction in runoff will affect the ability to irrigate crops and will reduce summer stream flows necessary to keep dams and reservoirs replenished.

According to a UN climate report, the Himalayan glaciers that are the principal dry-season water sources of Asia's biggest rivers - Ganges, Indus, Brahmaputra, Yangtze, Mekong, Salween and Yellow - could disappear by 2035 as temperatures rise.[17] Approximately 2.4 billion people live in the drainage basin of the Himalayan rivers.[18] India, China, Pakistan, Afghanistan, Bangladesh, Nepal and Myanmar could experience floods followed by severe droughts in coming decades.[19] In India alone, the Ganges provides water for drinking and farming for more than 500 million people.[20][21]

[edit] Ozone and UV-B

Some scientists think agriculture could be affected by any decrease in stratospheric ozone, which could increase biologically dangerous ultraviolet radiation B. Excess ultraviolet radiation B can directly effect plant physiology and cause massive amounts of mutations, and indirectly through changed pollinator behavior, though such changes are difficult to quantify.[22] However, it has not yet been ascertained whether an increase in greenhouse gases would decrease stratospheric ozone levels.

In addition, a possible effect of rising temperatures is significantly higher levels of ground-level ozone, which would substantially lower yields.[23]

[edit] Impact of agriculture on climate change

The agricultural sector is a driving force in the gas emissions and land use effects thought to cause climate change. In addition to being a significant user of land and consumer of fossil fuel, agriculture contributes directly to greenhouse gas emissions through practices such as rice production and the raising of livestock[24]; according to the Intergovernmental Panel on Climate Change, the three main causes of the increase in greenhouse gases observed over the past 250 years have been fossil fuels, land use, and agriculture.[25]

[edit] Land use

Agriculture contributes to greenhouse gas increases through land use in four main ways:

Together, these agricultural processes comprise 54% of methane emissions, roughly 80% of nitrous oxide emissions, and virtually all carbon dioxide emissions tied to land use.[26]

The planet's major changes to land cover since 1750 have resulted from deforestation in temperate regions: when forests and woodlands are cleared to make room for fields and pastures, the albedo of the affected area increases, which can result in either warming or cooling effects, depending on local conditions. [27] Deforestation also affects regional carbon reuptake, which can result in increased concentrations of CO2, the dominant greenhouse gas.[28] Land-clearing methods such as slash and burn compound these effects by burning biomatter, which directly releases greenhouse gases and particulate matter such as soot into the air.

[edit] Livestock

Livestock and livestock-related activities such as deforestation and increasingly fuel-intensive farming practices are responsible for over 18% of human-made greenhouse gas emissions, including:

Livestock activities also contribute disproportionately to land-use effects, since crops such as corn and alfalfa are cultivated in order to feed the animals.

Worldwide, livestock production occupies 70% of all land used for agriculture, or 30% of the land surface of the Earth.[30]

[edit] See also

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[edit] References

  • Fischer G., Shah M. and van Velthuizen H. (2002) "Climate Change and Agricultural Vulnerability". International Institute for Applied Systems Analysis. Report prepared under UN Institutional Contract Agreement 1113 for World Summit on Sustainable Development. Laxenburg, Austria
  1. ^ Intergovermental Panel on Climate Change Special Report on Emissions Scenarios retrieved 26 Jun 2007
  2. ^ UN Report on Climate Change retrieved 25 Jun 2007
  3. ^ "Climate 'could devastate crops'", BBC News Online, 31 January 2008. 
  4. ^ Lobell DB, Burke MB, Tebaldi C, Mastrandrea MD, Falcon WP, Naylor RL (2008). "Prioritizing climate change adaptation needs for food security in 2030". Science 319 (5863): 607–10. doi:10.1126/science.1152339. PMID 18239122. 
  5. ^ Australian Drought and Climate Change, retrieved on June 7th 2007.
  6. ^ NOAA (2006-01-30). "NOAA reports 2005 global temperature similar to 1998 record warm year". Press release.
  7. ^ Climate change, agricultural policy and poverty reduction – how much do we know?. Overseas Development Institute (2007).
  8. ^ Royal Society (2005) Impact of climate change on crops worse than previously thought http://royalsociety.org/news.asp?id=3084
  9. ^ Climate Change 2001: Working Group II: Impacts, Adaptation and Vulnerability IPCC
  10. ^ The Food, the Bad, and the Ugly Scherer, Glenn Grist July, 2005
  11. ^ Plague of plenty New Scientist Archive
  12. ^ The Food, the Bad, and the Ugly Scherer, Glenn Grist July, 2005
  13. ^ German Research Indicates Warming in Siberia, Global Warming Today, Global Warming Today
  14. ^ Federal Service for Hydrometeorology and Environmental Monitoring 5Roshydromet), Strategic Forecast of Climate Change in the Russian Federation 2010–2015 and Its Impact on Sectors of the Russian Economy (Moscow 2005)
  15. ^ The Danger of Climate Change for Russia – Expected Losses and Recommendations, By Alexey O. Kokorin and Inna G. Gritsevich, Moscow, russian analytical digest 23/07 [1]
  16. ^ Global warming 'will hurt Russia', 14:23 03 October 2003, NewScientist.com news service
  17. ^ Vanishing Himalayan Glaciers Threaten a Billion
  18. ^ Big melt threatens millions, says UN
  19. ^ Glaciers melting at alarming speed
  20. ^ Ganges, Indus may not survive: climatologists
  21. ^ Himalaya glaciers melt unnoticed
  22. ^ Ozone layer most fragile on record Brown, Paul The Guardian April 2005
  23. ^ Dead link: http://news.independent.co.uk/world/environment/story.jsp?story=633349
  24. ^ Food and Agriculture Organization of the UN retrieved 25 Jun 2007
  25. ^ Intergovernmental Panel on Climate Change (IPCC)
  26. ^ Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios retrieved 26 Jun 2007
  27. ^ Intergovernmental Panel on Climate Change
  28. ^ IPCC Technical Summary retrieved 25 June 2007
  29. ^ Food and Agricultural Organization of the U.N. retrieved 25 jun 2007
  30. ^ Food and Agricultural Organization of the U.N. retrieved 27 jun 2007

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