LAHORE: Pakistan is unlikely to achieve its economic targets in the current fiscal year given the way its agrarian economy has been battered in devastating summer floods. There is mounting concern in the scientific community that the floods were mainly attributable the phenomena of ‘global warming’.
The threat of global climate change has caused alarm among scientists as crop growth is severely affected by changes in key climatic variables (i.e., rainfall and temperature) with a detrimental effect on agricultural production and in turn, food security. Although the effects of climate change on crop yields are likely to vary greatly between regions; anticipated changes are expected to have a large and disproportionate impact predominantly in tropical zones of the developing world with precipitation regimes ranging from semiarid to humid.
Hazards include increased flooding in low lying regions, greater frequency and severity of droughts in semiarid areas, and excessive heat conditions, all of which can limit crop growth and yields. The Intergovernmental Panel on Climate Change (IPCC) in its fourth assessment report (IPCC 2007) warns that warming by 2100 will be worse than previously expected, with a probable temperature rise of 1.8C to 4C and a possible rise to as high as 6.4C. As temperatures continue to rise, the impact on agriculture will be significant.
The pronounced consequences of climatic change on agricultural crops are likely to trigger a shift of crop potential. The areas which at present are judged to be most suited to a given crop or combination of crops, may no longer remain as such after a climatic shift. Pakistan’s agricultural cropping pattern is unique in the sense that climatic conditions in particular parts of the country have given rise to cultivation of Rabi and Kharif season crops. But under the looming scenario, these categories will be substantially altered.
The menace of climate change is also likely to catalyse the phenomena of genetic erosion in the near future. It will both threaten the survival of individual species and alter the way the different elements of biodiversity interact in food and agriculture ecosystems.
These interactions allow for pollination, soil fertilisation and the natural biological control of plant and animal diseases. The IPCC reports that a significant number of species will be at risk of extinction as the global mean temperature rises. Of particular concern are relatives of major crops surviving in the world. Crop wild relatives are already under severe threat due to habitat loss and environmental degradation. Climate change may drive them to extinction.
The impact of global warming will also be felt in the soil, where warmer conditions are likely to hasten the natural decomposition of organic matter and to increase the rates of other soil processes that ultimately affect its fertility. Addition application of fertiliser may be needed to counteract these processes and to take advantage of the potential for enhanced crop growth that can result from increased atmospheric carbon dioxide (CO2). This can come at the cost of environmental risk for additional use of chemicals may impact water and air quality. The continual cycling of plant nutrients-carbon, nitrogen, phosphorus, potassium, and sulfur in the soil plant-atmosphere system is also likely to accelerate in warmer conditions, enhancing carbon dioxide and Nitrous oxide and other green house gas emissions.
Nitrogen is made available to plants through bacteria in the soil. This process of nitrogen fixation, associated with the greater root development, is also predicted to increase in warmer conditions and with higher carbon dioxide levels, if soil moisture is not limiting. Agriculture of any kind is strongly influenced by the availability of water. Climate change will modify rainfall, evaporation, runoff, and soil moisture storage. Changes in total seasonal precipitation or in its pattern of availability are both important.
The occurrence of moisture stress during flowering, pollination and grain filling is harmful to most crops and particularly to corn and wheat. The phenomenon of global warming has altered the ‘water use efficiency’ of crops requiring greater water use. Therefore there will be substantial increase in the need for irrigation, which will probably lead to higher cost of production and possible shifts towards less water demanding uses. Moreover increased evaporation from the soil and accelerated transpiration in the plants themselves will cause moisture stress; as a result there will be a need to develop crop varieties with greater drought tolerance.
The demand for water for irrigation is projected to rise in a warmer climate, bringing increased competition between agriculture- already the largest consumer of water resources in semi arid regions-and urban as well as industrial usage. Falling water tables and the resulting increase in the energy needed to pump water will make irrigation more expensive, particularly where drier conditions prevail.
Plants grow through well known process of photosynthesis, utilizing the energy of sunlight to convert water from the soil and CO2 from the air into sugar, starch, and cellulose-carbohydrates that are the foundations of the entire food chain. Researchers have gauged that that for many plant species doubling of CO2 will lead to 10-15 percent increase in dry matter production provided all other factors remain constant.
Conditions are more favorable for the proliferation of insect pests in warmer climates. 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 over winter in areas where they are now limited by cold, thus causing greater infestation during the following crop season. The population of the Cotton White flies in cotton growing areas and boost incidence of Cotton Leaf Curl Virus because whiteflies act as disease carriers. The disease costs loss running into millions of rupees to the ailing agrarian economy of the country. Altered wind patterns may change the spread of both wind borne pests and of the bacteria and fungi that are agents of crop disease. Crop-pest interactions may shift as the timings of development stages in both hosts and pests is altered. The possible increase in pest infestation may bring about greater use of chemical pesticides to control them, a situation that will require the further development and application of Integrated Pest Management (IPM).
Climate change threatens to uproot many rural communities. Increasing frequency of droughts brought on by climate change may leave farmers and pastoralists who rely on rainfall to raise their crops and livestock with no alternative but to abandon their land. This displacement of people is likely to result in competition between migrants and the established communities for access to land and further aggravate the pressure placed on scarce resources. These challenges which will likely rear their heads in the near future need clear-headed and concerted planning.
How global warming will alter farming
