Climate Change: A threat to Agriculture
April 12, 2013
Muhammad Awais, Syed Aftab Wajid and Muhammad Naveed Arshad
Pakistan is an important Agricultural country of South Asia. Although contribution of agriculture in GDP has decreased from 53 % in 1950 to 21.8 % in 2012 but it still has a prominent position in the economy of Pakistan. According to economic survey of Pakistan 2011-12 population of Pakistan has reached upto 180 million and 62 % of this population has engaged with this sector directly or indirectly.
Agriculture is strongly associated with poverty alleviation, food safety and rural development. Agriculture is totally dependent on prevailing weather conditions. Climate change is a burning issue of agriculture and geographical location of Pakistan makes it more vulnerable to vagaries of Climate Change.
According to World Bank, Pakistan is the 12th most vulnerable country to climate change. Climate change is basically induced due to increased emissions of greenhouse gases (carbon dioxide, methane, nitrous oxide) from deforestation, industrialization, fossil fuel burning and unchecked use of agrochemicals.
Human activities are responsible for this newly evolving CO2 and methane enriched atmosphere as since the 1750 carbon dioxide and methane concentration has increased from 280 parts per million (ppm) and 716 (parts per billion) to 393 ppm and 1774 ppb, respectively. Greenhouse gases are being added to the atmosphere at a rate of 23 ppm per decade. Earth’s atmosphere allows incoming sunlight to pass through but absorbs heat radiated back from the earth’s surface (Greenhouse effect) resulting increase in the earth’s overall temperature (Global warming).
Climate change is likely to result in occurrence of more frequent and intensified hydro events and increased temperature during the coming century. According to the Intergovernmental Panel on Climate Change (IPCC), the average temperature of the earth has increased by 0.6 °C during the previous century and it is predicted to increase by 1.4 to 5.8 °C by the end of the current century. Some levels of GHGs are essential to maintain temperatures needed to support life. The earth,s mean temperature is 15°C, and without greenhouse gases it would be -18 °C, that is not suitable for earth life.
Positive influences of climate change on agriculture are expected to arise from carbon fertilization effect. Doubling carbon dioxide concentration in atmosphere can increase crop photosynthesis by 50 % and its yield by 30 % but increased temperature with increasing carbon dioxide (greenhouse effect) will not only offset the positive effects of carbon dioxide, but also cause a reduction in crop yield in subtropical and tropical areas.
Increased carbon dioxide concentration influences the plant processes in two ways. First, it accelerates the photosynthetic rate and secondly it reduces the transpiration rate by partial closing of stomata. Stomatal conductance for water vapors decreases about 40 % in response to doubling of carbon dioxide that ultimately would decrease water loss and increase water use efficiency of the crop.
Decreased transpiration rate will increase the crop canopy temperature by 1-2°C, that have a positive effect on crop yield in temperate regions and negative effect in tropical areas. Increasing carbon dioxide concentration have a negative effect on grain quality of major crops like wheat, rice etc. Plants absorb less nitrogen under increased carbon dioxide concentration, so crops produce grains with low protein contents.
Negative effect of climate change on agriculture was mainly due to increased temperature. Increased temperature decreases the crop growth duration to remain photosynthetically active, so less assimilates are produced in the grain that finally leads to reduced quality and quantity of yield. According to the Intergovernmental Panel on Climate Change (IPCC), cereal production was decreased upto 30% in south Asia mainly due to increased temperature and water scarcity. Pakistani rivers received 80% of total water from the glaciers of Hindukash and Hamaliya.
The average temperature of Hamaliya has increased by 1°C and it was predicted that it would increase further by 3°C at the end of this century. Increased temperature accelerates the melting rate of these two glaciers.
Weeds use carbon dioxide more efficiently than the crop plants so increased carbon dioxide concentration has a positive effect on weed infestation. Insects and pest that were killed due to very low temperature of winter season become more dangerous for crops under high temperature conditions.
Rainfall will occur frequently in sub-humid and humid areas of Pakistan under climate changed conditions leading to increased humidity and thus more fungal attack on the crops. Mean sea level has been also predicted to increase by 1 meter at the end of current century that would lead to salinity and thus loss of precious agricultural land in coastal areas.