Saturday, November 8, 2008

How climate change will impact agriculture

As the earth warms, it is likely that crop-producing areas will expand northwards to ice-bound regions in Greenland, Canada and Russia. At higher latitudes, global warming will extend the length of the growing season, with a shorter snow-bound period. This could allow for earlier planting of crops and the possibility of two crops instead of just the one, as is now being practised. On the other hand, crops adapted to the temperatures and day lengths of the plains and lower latitudes may not respond well to the changed conditions.

In the warmer plains regions, increased temperatures may speed up the rate at which plants release carbon dioxide in the process of respiration, resulting in less than optimal conditions for net growth. When temperatures exceed the optimal for biological processes, plants respond with a drop in yield. If minimum night-time temperatures rise significantly -- as is expected from greenhouse warming projections -- higher night-time respiration may also reduce potential yields. Another important effect could be accelerated physiological development, resulting in premature maturation and therefore reduced yields.

Photosynthesis is the foundation of plant growth. It is the process by which energy from sunlight converts water from the soil and carbon dioxide from the air into sugar, starch and cellulose, making plants grow. Carbon dioxide enters a plant through its leaves. Greater concentrations of CO2 in the air result in higher CO2 uptake and greater conversion to carbohydrates.

Crop species vary in their response to CO2. Wheat, rice and soybean are called C3 plants and respond readily to increased CO2 levels. Corn, sorghum, sugarcane and millet are C4 plants that follow a different pathway and are more efficient photosynthetically than C3 crops. So far, these distinctions have been demonstrated only under experimental conditions such as growth chambers and greenhouses. Experimental studies on the long-term effects of CO2 in realistic field settings have not yet been done on a comprehensive scale.

Higher levels of atmospheric CO2 also induce plants to close small leaf openings known as stomata through which CO2 is absorbed and water vapour is released. Thus, under greater CO2 conditions, crops may use less water (by closing their stomata) even as they produce more carbohydrates. This dual effect will likely improve water-use efficiency, which is the ratio between crop biomass and the amount of water consumed. At the same time, climatic effects such as higher temperatures and changes in rainfall and soil moisture could either enhance or negate the potentially beneficial effects of enhanced atmospheric CO2 on crop physiology.

Water stress will be a critical feature of climate change and global warming. It will modify rainfall, evaporation, surface runoff and soil moisture storage. If temperatures and rainfall patterns turn adverse, soil moisture stress will result from increased evaporation from the soil and accelerated transpiration in plants. Moisture stress during flowering, pollination and grain-filling is harmful to almost all crops, but the most susceptible crops are corn, soybean and wheat which are likely to suffer the worst damage when there is a shortage of soil moisture. The predictable response to this eventuality is to develop crop varieties with greater drought tolerance, those that can withstand moisture stress.

Another problem will be more pests and a wider range of these pests. Insect pests proliferate more readily in warmer climates since conditions for growth and multiplication are more favourable compared to cooler conditions. The incidence of other crop diseases like fungal and bacterial infection is also likely to increase if the climate gets warmer.

In temperate areas, longer growing seasons will enable insects to complete a greater number of reproductive cycles during the spring, summer and autumn. Warmer winter temperatures may also allow larvae to survive the winter in areas where they are now limited by cold, thus causing greater infestation during the following crop season.

Storms and hurricanes and changed wind directions are likely to alter the spread of both windborne pests and of bacteria and fungi that are agents of crop disease. Crop-pest interactions may shift as the timing of development stages in both hosts and pests is altered. Livestock diseases may be similarly affected.

For agriculture-dependent economies like India and other countries in Asia, it is very important to start planning both mitigating and adaptive strategies to minimise the risks to agricultural productivity and the livelihoods of rural people.

A number of adaptive actions may be taken to minimise the adverse effects of climate change on agriculture. Farm-level adjustments may include the introduction of very early- or late-maturing crop varieties to beat the vulnerable period. Changing varieties and crop cycles, adjusting the timing of field operations and conserving soil moisture through appropriate tillage methods are other steps to mitigate the effects of climate change.

Some options like changing crop varieties may be inexpensive, but others like rainwater conservation and technologies for conservative use of water will involve major investments.

An additional economic aspect is adjustments in regional production centres and adjustments of capital, labour, and land allocations. For example, commodity production could move to regions where there is better comparative advantage. Studies show that, in general, market adjustments can indeed moderate the impact of reduced yields, but these shifts are likely to work against the interests of developing countries.

A major adaptive response will be the breeding of heat- and drought-resistant crop varieties by utilising genetic resources in the form of traditional crop varieties. These contain a range of genes that could be selected for their ability to withstand extremes in atmospheric conditions and bred into new crop varieties. Collections of such genetic resources are maintained in germplasm banks. These must be increased in number, particularly in diversity-rich regions where there is high diversity of crop germplasm. Such banks must be made accessible to farmers and breeders.

Adaptation has limits and it is not as though these formulae will lead to guaranteed success. Sometimes it may be difficult for better adapted new crops to find ready markets. If, for instance, major shifts are to be made from grain to fruit and vegetable production, farmers could find themselves more exposed to marketing problems and credit crises brought on by higher capital and operating costs.

While changes in planting schedules or in crop varieties may be readily adopted, modifying the types of crops grown does not ensure equal levels of productivity or nutritional quality. Nor can it guarantee equal profits for farmers. Expanded irrigation may lead to groundwater depletion, soil salinisation and waterlogging. Increased demand for water by competing sectors may limit the viability of irrigation as an adaptation to climate change. Expansion of irrigation as a response to climate change will be difficult and costly even under the best circumstances. Mounting societal pressures to reduce environmental damage from agriculture will likely foster an increase in protective regulatory policies that could further complicate the process of adaptation.

Coping with climate change and its impact on agriculture and rural livelihoods is going to be a long haul. It’s an irony that those who have caused global warming -- the high-emission polluters in developed countries -- are going to be the beneficiaries of climate change not its victims, as far as food production is concerned. The world community needs to come together to discuss mitigation and adaptation strategies to counter global warming and climate change, so that the poor are not made to carry the full burden of this man-made disaster.

By Suman Sahai , a PhD in genetics. She is the Director of Gene Campaign, a leading research and advocacy organisation working on farmer and community rights, bio-resources, IPR, indigenous knowledge and GE food and crops.


Forget yourself for others, and others will never forget you.

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