The Hindu Business Line : Emissions

According to scientists, agriculture is responsible for up to half of all methane emissions. Though it persists for a shorter time in the atmosphere, methane is about 20 times more powerful than CO{-2} in its warming action.

G. Chandrashekhar

Scientists now recognise that over the next 30 years, many agriculture-related environmental problems will remain serious. However, while some problems may deepen more slowly than in the past, some may even be reversed.

Global warming and climate change have now become buzzwords the world over.

What is the connection between agriculture and climate change? Agriculture is a major source of greenhouse gas emissions. It releases large quantities of carbon dioxide (CO{-2}) through the burning of biomass, mainly in the areas of deforestation and grasslands.

Methane emissions

According to scientists, agriculture is also responsible for up to half of all methane emissions. Though it persists for a shorter time in the atmosphere, methane is about 20 times more powerful than CO{-2} in its warming action. Methane is thus a major short-term contributor to global warming.

According to the Food and Agriculture Organisation (FAO), annual anthropogenic emissions are around 540 million tonnes, and are growing at around 5 per cent per year. Livestock alone accounts for about a quarter of methane emissions, by way of gut fermentation and the decay of excreta. As livestock numbers grow, and as livestock rearing becomes increasingly industrial, the production of manure is projected to rise by about 60 per cent by 2030. Methane emissions from livestock are likely to increase by the same proportion.

Rice farming

Similar to livestock, rice farming under irrigated conditions is another major source of methane, accounting for a fifth of total anthropogenic emissions. The area under rice is likely to rise gradually in the coming years.

Close to 90 per cent of world rice production takes place in Asia (China, India, Pakistan, Bangladesh, the Philippines, Vietnam, Thailand, Indonesia, Cambodia and Myanmar, to name a few), making the region more vulnerable than others.

However, following recognition of the risks arising out of methane emissions, adoption of appropriate technology and practices — better controlled irrigation and nutrient management as also rice varieties that emit less methane — may help mitigate the danger to some extent in the future.

Agriculture is a key source of another greenhouse gas — nitrous oxide — which is generated by natural processes but is boosted by leaching, volatilisation and run-off of nitrogen fertilisers, and by the breakdown of crop residues and animal wastes.

If you thought agriculture was only the source of greenhouse gas emissions, think again. Interestingly, agriculture is also a sink for carbon. However, it is believed that soils and other biological sinks such as vegetation have an inherent upper limit for storage.

Carbon sink

The total amount of carbon that can be stored is both crop-specific and location-specific. The rate of sequestration declines after a few years of growth before eventually reaching the limit. In 1997-1999, an estimated 590 to 1,180 million tonnes of carbon were locked up in cropland soils alone, in the form of soil organic matter from crop residues and manure, the FAO has said, adding that projections of increased crop production imply that, by 2030, this total could rise by 50 per cent.

Climate change will impact global agriculture, including forestry and fisheries, in many different ways — both positive and negative. Average global temperatures are projected to rise by between 1.4 and 5.8 degrees Celsius by 2100; but over the next two decades or so, the rise will come down between 1 and 3 degrees Celsius. In the next 25 years, climate change may not depress global food availability but it may increase the dependence of developing countries on food imports and accentuate food insecurity for vulnerable groups and countries.

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