HUMAN DIMENSIONS OF GLOBAL CLIMATE CHANGE : Will Agricultural Practices Aggravate The Problem?
K. Chatterjee

Agriculture and climate are inextricably related.  The dependence of agriculture on climate has been recognised for a long time while the contribution of agriculture to climate change has only been established over the last few decades.  Agriculture and related activities, including clearing of forests, burning plant matter, cultivating rice, raising livestock and using fertilizers, contribute greenhouse gases to the atmosphere.  Fourteen percent of global warming is contributed by present agricultural practices.

Biomass burning, which is an agriculture related activity contributes approximately 10-20 percnet of total annual methane (CH₄) emissions, 5-15 percent of N₂O emissions, 10-35  percent of CO₂ emissions, in addition to contributing to atmoshperic CO₂.

In a study carried out by FAO entitled “Agriculture:Towards 2000”, the aim has been to develop long term strategies to raise food production in 90 developing countries.  The goal can be achieved through increase in area of arable land as well as intensification of production per hectare.  Land clearing for increase in the area of arable and contributes to considerable greenhouse gas build ups.  Clearing forest land for agricultural purposes results in increased carbon emissions, because forest eco-systems store 20-100 times more carbon per unit area than crop land.

Lowered yields in food production as a consequence of global climate change induced by increased greenhouse warming, UV-B and ground level ozone need to be taken into account while projecting food grain production.  The present  agricultural practices globally use considerable quantity of chemical pesticides and fertilizer.  Though pesticides have been the key components of the Green Revolution and of strategies of the developing countries to attain food grain self sufficiency, they are known to have adverse affects on human health, through food and drinking water and also affect animal life.

Studies suggest that an increase in temperature due to climate change may extend the geographic range of some insect pests.  An important unknown, however, is the effect the change in precipitation and humidity will have on the insect pests themselves and on their predators, parasites and diseases.  (US Environmental Protection Agency: 1989)

Climate change may significantly influence interspecific interactions between pests and their predators and parasites.
Most agricultural diseases reach severe levels under warmer and more humid conditions.  In addition, increases in population levels of disease vectors may well lead to an increase in the number of epidemics.

Pesticides and the environment
Pesticides are chemical agents used for controlling insects, pests, weeds, fungus etc.  The total number of pesticides available in the market is of the order of 600, of which 150 are insecticides.  (Back, Koemanm, 1984).

Use of pesticides in controlling pests has resulted in the disruption of ecosystems because of the death of non-target species, accumulation of pesticide residues in the environment and in food, and the build up of pesticide resistance in target species.

The pesticide that is not lost by volatilisation or in runoff enters the soil where it is eventually degraded or it percolates to the groundwater table.  The time required for degradation varies greatly according to the type of pesticide.  Some products break down readily in the soil; others particularly the organ chlorines, can resist degradation for decades and are hence non-biodegradable.  The possibility of the pesticide being retained in the soil also depends upon the type of soil and mode of application.  In general, the absorptive capacity is highest in organic rich soils, and is least in sandy soils.

Finally, a proportion of the pesticide that is not degraded will leach below the root zone and eventually end up in the ground water.  In permeable soils about one percent of the original pesticide application may be leached.

Environmental contamination by pesticides, is now widespread with serious implications on wildlife and aquatic life.

Butterflies and pollinating insects like honeybees are frequently killed in large numbers when spraying occurs near or on flowers.  Wildlife is also affected through pesticide contamination of water and soil.

Since the Second World War, much of the growth in pesticide use has been a reflection of high return and low costs relative to those of other inputs, such as fertilisers and seeds.  These insecticide have been the key components of the Green Revolution and of strategies of the developing countries to attain food grain self sufficiency.  These are also known to be responsible for impacting human health.  Estimates suggest that in developing countries, some 3 million suffer from single short term exposure with 220,000 deaths; death rates vary from 1 percent to 9 percent in cases undergoing treatment.  Over 7000,000 people a year suffer from chronic long term exposures.

The largest users of pesticides are the United States, and the former USSR, although on a per hectare basis European countries use higher levels.

The use of chemicals in pest control has a poor reputation due to the deleterious environmental effects of a number of pesticides noted during the last decades.

In UK, the level of exposure of the general population to residues is assessed by means of the Total Diet Study.  Food was divided into 20 food groups - bread, meat, poultry, fish, fresh fruit, milk etc.  The study revealed a steady decline in organochlorine intake sine 1966.  In fact, in the 1960s only dieldrin was close to the maximum Acceptable Daily Intake (ADI).  The ADI, based on the average body weight of 70 kg, is for DDT + TDE + DDE (350.00 mg/person/day) and Lindane (700.0 mg/person/day).

In developing countries, the daily intake of cereals in total diets is very high.  Diet studies in five states in India have revealed intakes exceeding the Acceptable Daily Intake.

The farmers of the developing countries should look for alternatives to maximise the use of safe, cheap and simple pest management techniques including those traditionally used by Third World farmers, and to integrate these with the use of the safest possible chemical pesticides, where necessary, into a strategy which could deal with pest problems as a part of a system - including people, crops, beneficial insects, fish and livestock, as well as pests and chemicals.  Such an ecological approach constitutes the best use of pesticides.  It is also the basis of the idea of Integrated Pest Management (IPM).  IPM can draw upon a number of different pest management methods.  These include the careful and selective use of pesticides as well as biological and cultural controls, physical controls, the use of pesticides as well as biological and cultural controls, physical controls, the use of pest resistant plant varieties and a number of other techniques.  (Bull, 1982)

Use of fertilizers
In 1978/79, developed countries used about three-quarters of world consumption of fertilizers and the US alone consumed over one-third of all pesticides used.  The balance is shifting rapidly, however, as it must in the interest of global food security.  In the developing countries, average fertiliser rates are a great deal lower.  The annual application to arable and permanent crops in Asia is currently about 30 Kg N/ha, in Latin America 15 Kg N/ha and in Africa only 4 Kg N/ha, and much of the land receives no inorganic fertiliser at all.  The use of fertilizers has been growing more than twice as fast in developing as in developed countries (averaging 10 percent a year between 1960/70 and 1978/79) and the FAO projects future growth by the year 2000 to be between 7.5 and 8 percent per year, twice the projected increase in crop production. (FAO, 1987).

Water resources are particularly sensitive to the run-off of nitrogen and phosphates from excess use of fertilizers.  Many rivers in the United Kingdom, despite considerable year to year variation, show a progressive increase in nitrate concentration over the past 30 to 40 years.  Several important rivers have mean values gretater than 50 mg/l (European community limit).  In the United States, although many rivers are also showing increasing trends in nitrate contamination, the majority are still substantially below 45 mg/l nitrate in ground water.

Ground water is a primary source of drinking water for a large percentage of people both from the developed and developing countries.  Nitrate contamination of groundwater is therefore a matter of concern.

Nitrate pollution of water is a health hazard, particularly for infants and the percolation of nitrogen to the underground water sources can impose a heavy cost on a community, or region.

Eutrophication is the process by which the nutrients contained in fertilizers not only promote the growth of crops but also of wild plants, including weeds, wild flowers, shrubs and trees in the vicinity of fertilizer use, as well as algae, aquatic plants in rivers, lakes, estuaries and even, in the sea increasing the burden on water’s limited supply of dissolved oxygen.

Nitrous oxide (N2O) is only present in small amounts in the atmosphere (pre industrail atmoshperic concentration of N2O was 288 per billion by volume (ppbv) while present day concentration is 310 ppbv).  Its potential impact on climate is 230 times greater per molecule added.  N2O is known to contribute to the depletion of the stratospheric ozone layer.

Human activities like the fossil fuel combustion, biomass burning, land clearing, and addition of nitrogenous fertilizers to the soil increase N2O production, but, estimates of fertilizer induced N2O emissions are highly variable.

The 1993 global population of 5.7 billion is projected to increase to 6.25 billion in 2000; 8.5 billion by 2025.  This is bound to put tremendous pressure on cultivated land to provide food.  The problem has been further aggravated by the present exploitive agricultural practices e.g. use of pesticides and chemical fertilizers.  The human induced greenhouse warming resulting in climate change will impose additional stress to the world food security and production system.  Therefore there is a need to take up country specific studies on the human dimensions of global climate change on a priority basis.

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