The Author is a Senior Research Fellow at the School of Environmental Sciences, Jawaharlal Nehru University, in New Delhi, India. → See also:
The atmosphere surrounding the earth is made up of nitrogen (78%), oxygen (21%) and the remaining 1%, is made up of trace gases (called so because they are present in very small quantities) that include carbon dioxide, methane and nitrous oxide. These gases also called greenhouse gases act as a blanket and trap heat radiating from the earth and make the atmosphere warm. Beginning with the industrial revolution global atmospheric concentrations of these greenhouse gases have increased markedly as a result of human activities. The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land use change, while those of methane and nitrous oxide are primarily due to agriculture. As a result we are witnessing global warming.
The increasing green-house gases (GHG) resulted in global warming by 0.74°C over past100 years and 11 of the 12 warmest years were recorded during 1995 – 2006. The Intergovernmental Panel for Climate Change (IPCC) projections on temperature predicts an increase of 1.8 to 4.0°C, by the end of this century. Some changes will affect agriculture through their direct and indirect affects on crops, soils, livestock, fisheries and pests. Tropical countries are likely to be affected more compared the countries situated in temperate regions. The brunt of environmental changes is expected to be very high in India due to greater dependence on agriculture, limited natural resources, alarming increase in human and livestock population, changing pattern in land use and socio-economic factors that pose a great threat in meeting the food, fibre, fuel and fodder requirement. There is a likelihood of a considerable impact on agricultural land-use due to snow melt, availability of irrigation, frequency and intensity of inter- and intra- seasonal droughts and floods, soil organic transformation matters, soil erosion and availability of energy as a consequence of global warming, impacting agricultural production and hence, the nations’ food security. Global warming due to greenhouse effect is expected to impact hydrological cycle viz. precipitation, evapo-transpiration, soil moisture etc., which would pose new challenges for agriculture.
The global atmospheric concentration of carbon dioxide, a greenhouse gas (GHG) largely responsible for global warming, has increased from a pre-industrial value of about 280 ppm to 379 ppm in 2005. Similarly, the global atmospheric concentration of methane and nitrous oxides, other important GHGs, has also increased considerably. The increase in GHGs was 70% between 1970 and 2004. Eleven of the last twelve years rank among the 12 warmest years in the instrumental record of global surface temperature since 1850. The mean earth temperature has changed by 0.74°C during 1906 – 2005. Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. During last 50 years, cold days, cold nights and frost have become less frequent, while hot days, hot nights, and heat waves have become more frequent. The frequency of heavy precipitation events has increased over most land areas. Global average sea level rose at an average rate of 1.8 mm per year over 1961 to 2003. This rate was faster over 1993 to 2003, about 3.1 mm per year.
The projected temperature increase by the end of this century is likely to be in the range 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded. It is likely that future tropical cyclones will become more intense, with larger peak wind speeds and heavier precipitation. For the next two decades a warming of about 0.2°C per decade is projected. Even if all future emissions were stopped now, a further warming of about 0.1°C per decade would be expected. Himalayan glaciers and snow cover are projected to contract. It is very likely that hot extremes, heat waves, and heavy precipitation events will continue to become more frequent. Increases in the amount of precipitation are very likely in high-latitudes, while decreases are likely in most subtropical land regions, continuing observed patterns in recent trends. The projected sea level rise by the end of this century is likely to be 0.18 to 0.59 meters. Average global surface ocean pH is projected to reduce between 0.14 and 0.35 units over the 21st century.
Analyses done by the Indian Meteorology Department and the Indian Institute of Tropical Meteorology, Pune (MS), generally show the same trends for temperature, heat waves, glaciers, droughts and floods, and sea level rise as by the Intergovernmental Panel on Climate Change of United Nations. Magnitude of the change varies in some cases. At all India level, there is no trend in monsoon rainfall during last 100 years, but there are some regional patterns. Areas of increasing trend in monsoon rainfall are found along the west coast, north Andhra Pradesh and north-west India, and those of decreasing trend over east Madhya Pradesh and adjoining areas, north-east India and parts of Gujarat and Kerala (-6 to -8% of normal over 100 years). Surface air temperature for the period 1901 – 2000 indicates a significant warming of 0.4°C for 100 years. The spatial distribution of temperature changes indicated a significant warming trend has been observed along the west coast, central India, and interior Peninsula and over northeast India. However, cooling trend has been observed in northwest and some parts in southern India. Instrumental records over the past 130 years do not show any significant long-term trend in the frequencies of large-scale droughts or floods in the summer monsoon season. The total frequency of cyclonic storms that form over Bay Bengal has remained almost constant over the period 1887 – 1997. There are evidences that glaciers in Himalayas are receding at a rapid pace.
It is projected that by the end of the 21st century rainfall will increase by 15 – 31%, and the mean annual temperature will increase by 3°C to 6°C. The warming is more pronounced over land areas, with the maximum increase over northern India. The warming is also projected to be relatively greater in winter and post-monsoon seasons.
Although increase in carbon dioxide is likely to be beneficial to several crops, associated increase in temperatures, and increased variability of rainfall would considerably impact food production. Recent IPCC report and a few other global studies indicate a probability of 10 – 40% loss in crop production in India with increases in temperature by 2080 – 2100.
There are a few Indian studies on this theme and they generally confirm similar trend of agricultural decline with climate change. Recent studies done at the Indian Agricultural Research Institute indicate the possibility of loss of 4 – 5 million tons in wheat production in future with every rise of 1oC temperature throughout the growing period (but no adaptation benefits). It also assumes that irrigation would remain available in future at today’s levels. Losses for other crops are still uncertain but they are expected to be relatively smaller, especially for kharif crops.
It is, however, possible for farmers and other stakeholders to adapt to a limited extent and reduce the losses (possible adaptation options are described later in this document). Simple adaptations such as change in planting dates and crop varieties could help in reducing impacts of climate change to some extent. For example, the Indian Agricultural Research Institute study quoted above indicates that losses in wheat production in future can be reduced from 4 – 5 million tons to 1 – 2 million tons if a large percentage of farmers could change to timely planting and changed to better adapted varieties. This change of planting would, however, need to be examined from a cropping systems perspective.
Increasing climatic variability associated with global warming will, nevertheless, result in considerable seasonal/annual fluctuations in food production. All agricultural commodities even today are sensitive to such variability. Droughts, floods, tropical cyclones, heavy precipitation events, hot extremes, and heat waves are known to negatively impact agricultural production, and farmers’ livelihood. The projected increase in these events will result in greater instability in food production and threaten livelihood security of farmers.
Increasing glacier melt in Himalayas will affect availability of irrigation especially in the Indo-Gangetic plains, which, in turn, has large consequences on our food production.
Global warming in short-term is likely to favour agricultural production in temperate regions (largely northern Europe, North America) and negatively impact tropical crop production (South Asia, Africa). This is likely to have consequences on international food prices and trade and hence our food security.
Small changes in temperature and rainfall could have significant effect on quality of cereals, fruits, aromatic, and medicinal plants with resultant implications on their prices and trade.
Pathogens and insect populations are strongly dependent upon temperature and humidity. Increases in these parameters will change their population dynamics resulting in yield loss.
Global warming could increase water, shelter, and energy requirement of livestock for meeting projected milk demands. Climate change is likely to aggravate the heat stress in dairy animals, adversely affecting their productive and reproductive performance. A preliminary estimate indicates that global warming is likely to lead to a loss of 1.6 million tones in milk production in India by 2020.
Increasing sea and river water temperature is likely to affect fish breeding, migration, and harvests. A rise in temperature as small as 1°C could have important and rapid effects on the mortality of fish and their geographical distributions. Oil sardine fishery did not exist before 1976 in the northern latitudes and along the east coast as the resource was not available/and sea surface temperature (SST) were not congenial. With warming of sea surface, the oil sardine is able to find temperature to its preference especially in the northern latitudes and eastern longitudes, thereby extending the distributional boundaries and establishing fisheries in larger coastal areas.
Corals in Indian Ocean will be soon exposed to summer temperatures that will exceed the thermal thresholds observed over the last 20 years. Annual bleaching of corals will become almost a certainty from 2050.
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