Climate Change and Agriculture
In this write up, Dr M A Haque discusses what is climate change and the various factors responsible for it. He then goes on to elaborate how rise in temperature, the unpredictibily of rainfall, its reduction in some places and increase in other parts of the country will affect agriculture. In conclusion he advocates the need for planning for better water capture and storage, more efficient utilisation of water and adoption of crop varieties capable of withstanding climate change.
In recent years there is increasing realisation that climate change is one of the major issues confronting our planet. But at the same time there is also lack of understanding of exactly what is meant by climate change. Most people do not understand the differences between weather and climate. World Meteorological Organisation coined the term “Climatic Change” in 1966 to include all types of climatic variability which could stay for more than 10 years. When it was realised that human activities could drastically change the climate, the term climatic change was replaced by climate change. Weather is what we perceive regularly while Climate Change is long term change.
Evidences Supporting Climate Change:
To know how the Climate Change unfolded in past, ice cores have been used extensively. Cylindrical ice masses are drilled out from ice sheets or glaciers. Ice cores include small air bubbles, analysis of which provides information about the atmosphere prevalent when the ice was deposited. For example, reliable data about carbon dioxide concentration in the Earth’s atmosphere for thousands of years are now available.
Sea level rise also gives clue about rise in temperature. We know that water expands with rising temperature. With rise in Earth’s temperature, sea water volume increases resulting in sea level rise. Also, calcite found in the oceans is utilized to estimate the prevalent ocean temperature in the past. Calcite’s 18O/16O ratio provides information about the temperature when the deposition took place.
Reasons for Climate Change: Climate Change is the direct outcome of greenhouse effect, exhibited by several chemicals in the Earth’s atmosphere. If their concentrations rise, the greenhouse effect increases. Presently carbon dioxide is considered the most important contributor. In June 2016 the atmospheric carbon dioxide concentration went beyond 400 ppm, for the second successive year and worryingly, this will continue during our lifetime. Carbon dioxide and other greenhouse gases are released due to burning of coal, oil, gas etc. and also due to deforestation. As a result the Earth is becoming warmer with time and there is strong possibility that the 2016 change may become permanent, unless drastic steps are taken. Emission of carbon dioxide during 1970 was 14.9 Gigatonnes which reached 35.6 Gigatonnes by 2015. Once the gas enters the atmosphere it remains there for centuries. In December 2015 the IPCC remarked that to keep the world temperature rise below 2C with a 66% probability, only 2,900 billion tonnes of carbon dioxide could be allowed to enter the atmosphere between 1870 and 2100. But the average yearly release is about 35 billion tonnes. Another factor aggravating the problem of greenhouse effect is the decreasing global forest cover. In 1949 the total forest cover was 4.7 billion ha .which came down to 714.9 million ha by 2015. Forests act as important sink for carbon being used for photosynthesis by vegetation. Although generally ignored, methane in the recent past, has also become a major contributor to climate change. According to FAO methane emissions increased by about 100% in the past five decades due to agriculture, fisheries and forestry activities. Coal, oil and gas industries are other important contributors of atmospheric methane.
Nitrous oxide (N2O) is another important greenhouse gas. It retards movement of heat radiating from the Earth through the atmosphere, contributing to global warming. Nitrous oxide acts as an ODS (ozone depleting substance) too. Various biological processes, agriculatural activities and fuel burning produce this gas. Another group of chemicals, named F-gases, which include chlorofluorocarbons (CFCs), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs) and sulphur hexafluoride (SF6) used in industries, generally as substitutes for ODS show greenhouse effects up to 23000 times compared to carbon dioxide.
Climate Change and Agriculture:
Climate change can impact different aspects of agriculture and almost every crop will be affected as crops require specific conditions to grow. Wheat and rice grow better in warm environment but maize and sugarcane cannot grow well in high temperatures. Also, different crops require different degrees of rainfall. With temperature changes, rain patterns are also changing resulting in failure of certain crops in a particular area. Changes in rainfall patterns will also result in floods in certain areas, which will affect crops. These changes may result in food shortages, especially in vulnerable areas. Scientists are of the view that Brazil, China, parts of Africa and south-east Asia will suffer the most and large populations will face hunger. There is some consolation too. Rising temperatures will prove beneficial for crops in selected areas. But the overall global impact will be negative.
India, the second largest world producer of rice and wheat, would be the hardest hit by rising temperature. Crop yield would fall drastically. Dangers for rain fed areas will be more than for irrigated areas. Climate change is expected to reduce wheat production by 6 to 23% by the year 2050 and by 10 to 40% by the end of the current century, if the present trend continues. In general temperature rise of about 2C could reduce wheat grain yields widely. Northern India may have less impact as the region has higher potential productivity. Still yield reduction can be between 1.5 to 5.8% in sub-tropical region, while in tropical areas the reduction could be more. In Indo Gangetic Plains, major producer of wheat, heat stress is expected to reduce yield drastically. A group of Indian and Chinese researchers has warned that Indo-Gangetic plain will face severe droughts and floods due to climate change.
Central and south-central regions of India with warmer climate and also areas with late sowing are likely to suffer even more. Scientists say that temperatures higher than 13 and 27C for mean seasonal minimum and maximum will reduce the production substantially. Temperature rise will also affect Indian rice production with the eastern region bearing the brunt. Simultaneous reduction in insolation will reduce the numbers of grains per plan and the grains will not be healthy as the time available for the grains to fill will get reduced.
Water availability will become an important factor in yield reduction. Large parts of the world are facing water scarcity. With climate change the problem is likely to get worse. Weather conditions will change resulting in more rains in some regions while others will get less rain. Rainfall will be more unpredictable resulting in serious problems due to floods or droughts.
With rising temperature the issue of water stress will become more important. The total runoff will reduce in case of all the river basins of the country except Narmada and Tapti. Average annual rainfall in India is about 1170mm varying widely in different regions, total precipitation is about 4000bcm (billion cubic metre). But only about 1123bcm can be utilized due to various constraints. The per capita, utilizable water is 1086m³ which will come down to 760m³ 2050. Unfortunately, only 48% of country’s rainfall ends up in rivers and 18% remains utilizable. According to the National Commission for Integrated Water Resources Development (NCIWRD) about 83% of available water in the country is used for irrigation. The rest 17% meets the demand for domestic, industrial and other sectors. Total static groundwater available in India is about 10,812bcm. The average groundwater recharge rate of India’s river basins is about 260m³/day. Estimates suggest that India has about 432bcm of groundwater which is replenished annually through rain and river drainage. Out of that about 395bcm is utilizable. Estimates suggest that India is pumping out some 190km³ of underground water a year. Nature is refilling only 120km³, a shortfall of 70km³ per year. Consequence is that in large parts of the country water table is sinking. Agriculture is a big sufferer, poor and marginal farmers are worst affected. Climate change can affect soil properties too. Increasing soil temperature will decompose organic matter faster. In the long run crops will suffer nutrient deficiencies. Also, rising temperatures will also lead to spread of pests.
Under the circumstances it is essential that steps are taken to reduce climate change at global level. There is need for planning for better water capture and storage, more efficient utilization of water and adoption of crop varieties capable of withstanding climate change. These are few of the easier options.
(The author is Director (Retd), Ministry of Environment, Forest & Climate Change, GoI. Views expressed are personal.)