Food and fuel in a warmer world
p Farmland under
water after flash floods in Bangladesh. Extreme
weather events may become more frequent as a result
of climate change. (FAO/9367/T. Page) p
Farmland under water after flash floods in Bangladesh. Extreme weather events may become more frequent as a result of climate change. (FAO/9367/T. Page)
Higher temperatures will increase evaporation from plants and soil, worsening the water problems that already afflict many of the hotter (and poorer) countries. Agricultural pests and diseases may increase in some areas, along with human diseases that already threaten rural populations. Cyclones could become an even bigger threat to coastal fishing communities.
The pattern of the rise in temperature is as uncertain as its extent. The increase probably will not be consistent, even within regions. Northern Europe is a case in point. Much of it will have a milder climate and a longer growing season, but the countries that currently benefit from the Gulf Stream, the warm-water current from the Caribbean, may lose all or part of that benefit, as changes in water temperature interfere with the mechanisms that control its flow. So Ireland, the United Kingdom and parts of France could become colder.
Prospects for the developing world are just as uncertain. In a 1996 FAO study on the effect of climate change on cereals production, the best-case scenario left 12 million fewer people at risk of hunger by 2060, but the worst case suggested 300 million more hungry individuals.
Yet global warming could have some positive implications. Strangely, one is from carbon dioxide, or CO2, the best known of the greenhouse gases. It speeds growth of plants, as they are partly made of carbon.
Crop productivity has doubled over the last 100 years, and about 10-20 percent of the improvement may be due to the growth-enhancing effect of carbon dioxide. This may mask much of the negative effect of climate change on agriculture between now and 2030. Temperate areas will also benefit from a longer growing season. Changes in sea temperature may have unpredictable effects on fisheries, and there will be new pests and diseases. Despite this, temperate countries could do well.
Agriculture: victim or villain?
Agriculture is itself responsible for about a third of greenhouse-gas emissions, mostly because of carbon dioxide, or CO2. This is the most significant greenhouse gas, and agriculture plays a crucial part in determining how much of it is in the atmosphere.
Carbon dioxide is removed from the atmosphere by plants and converted through photosynthesis to its solid form, carbon, which makes much of the plant. In climate change terms this is called carbon sequestration. Another form of carbon sequestration is the burying of carbon dioxide in the ground, reducing the greenhouse effect. But when land is ploughed, carbon dioxide is released back to the atmosphere.
Alternatives include no-till and conservation agriculture, in which ploughing is eliminated. Instead farmers leave crop residues on the land to protect the soil from wind, encourage biological activity and create organic matter. These techniques reduce releases of carbon dioxide significantly. Global emissions of carbon dioxide in 2000, not counting natural emissions, were nearly 23 900 million tonnes. Suitably managed, cropland could sequester about 1 640 to 2 240 million tons of carbon. In the United States, better agricultural practices could sequester the equivalent of nearly 10 percent of the country's total carbon emissions.
The 'clean development mechanism' under the Kyoto Protocol (see accompanying story) allows wealthier countries to offset some of their own emissions by funding 'clean' development in the less wealthy ones.
"Sustainably managed forests and plantations as well as conservation agriculture could be good candidates," says Wulf Killmann, Chairman of FAO's Inter-Departmental Working Group on Climate Change. "Forestry is likely to be amongst the first beneficiaries of the CDM. Trees store a lot of carbon, and so do wood products. But agriculture too has potential for carbon sequestration."
Not just carbon
Agriculture is responsible for two other greenhouse gases:
Methane is a powerful greenhouse gas and much of it comes from livestock. But this project in Viet Nam promoted use of biogas digesters, so that the methane could be used by farming families for cooking fuel. (FAO/20220/L. Dematteis)
But the greatest source of greenhouse-gas emissions is the burning of fossil fuels, mostly unrelated to agriculture. Up to 20 percent of fossil fuel consumption could be replaced in the short term by using biomass as fuel, and agriculture and forestry can produce it. "Biomass is anything organic, non-fossil material of biological origin, including crops, agricultural residues, wood and animal waste," says Gustavo Best, Secretary of FAO's Inter-Departmental Working Group on Climate Change. "It does emit carbon when you get energy out of it. But when you grow more, that carbon is sequestered by being turned into plant matter. With fossil fuel that happens too, in theory, if you can wait a few million years."
Biomass energy is with us now. In Brazil 6 million cars are running partly on alcohol derived from sugar cane. China already has 10 million dung digesters which provide a clean cooking fuel and an organic fertilizer. Woodfuels contribute to 6 percent of the world's primary energy, and in developing countries even over 60 percent. Fast-growing grasses, oilseeds and agricultural residues offer great potential. The Kyoto Protocol's clean development mechanism could encourage this.
Agriculture contributes to climate change. But the tools are available that could put agriculture on the positive side of the climate change balance sheet. The challenge is to make it happen.
4 December 2001