The UN Panel on Climate Change is informing the world on what damage global warming can cause. But a recent study shows how temperature changes have already hit the global economy and Indian agriculture is suffering the brunt of it. The study proves that agriculture losses worth US$5 billion annually from 1981-2002 can be correlated to temperature rises over the period. The study published in 'Environmental Research Letters', a journal published from the UK, has shown that almost 30% of the variation in global agricultural yields can be explained by rise in temperature.

To keep up with the growth in human population, more food will have to be produced worldwide over the next 50 years than has been during the past 10,000 years combined, the experts said.

Production of wheat under climate change

The New Delhi-based Indian Agricultural Research Institute (IARI) has now warned that the country's annual wheat output could plunge by 4-5 million tonnes with every 1 degree Celsius rise in temperature. These projections cannot and should not be brushed aside as long term issues that have no immediacy. For, the adverse impact of temperature changes on wheat output has already been in evidence for the past few years and has contributed to the recent wheat crisis, transforming India from a wheat exporter to an importer and forcing the government to re-introduce curbs on the wheat trade.

Results of an experiment carried out by the Department of Agricultural Meteorology, B A College of Agriculture, Anand Agricultural University, says that global warming and greenhouse effect will have an impact on the yield of wheat and maize in the state. Wheat and maize yield will go down manifolds if the temperatures keep rising or falling.

The yield under temperature of four degree Celsius was only a little above 2,800 kg per hectare and a little above 2,500 kg per hectare under 5 degree Celsius. The base yield was fixed a little above 5,700 kg per hectare.

The wheat yield under reduced maximum temperature was best under minus five degree Celsius. Against the base yield fixed at little over 5,700 kg per hectare the wheat yield was almost 6,250 kg per hectare under minus five degree Celsius temperature.

This production decreased to 5,600 kg per hectare under minus four degree Celsius temperature. The yield took a further dip to a little below 5,500 kg per hectare mark under minus three degree Celsius.

While, under minus two degree Celsius the yield was only 5,250 kg per hectare and under minus one degree Celsius it was 4,700 kg per hectare. So, wheat will suffer tremendously under the increasing temperatures in the forthcoming years. The decrease in cultivation of wheat may further worsen the situation as more and more farmers are turning towards cash crops like cotton.

The estimated loss in wheat output is, however, based on the assumption that the availability of irrigation water would remain the same as it is now. But this seems unlikely in view of receding Himalayan glaciers and increasing nonagricultural use of water, the agenda note points out.

Production of maize

Maize varieties like GS-2 and GM-3 gave different results under this simulation. Maize GM-3 was found more vulnerable to elevated temperature (3-4 degree Celsius as compared to GS-2.

Both the cultivators responded well at elevated temperature of two degree Celsius. The GS-2 variety of maize production per hectare was 4,200 kg under the elevated maximum temperature of one degree Celsius against the normal yield of 4,000 kg per hectare. However, it increased to almost 4,800 kg per hectare under two degree Celsius temperature. The yield fell to 3,900 kg per hectare under five degree Celsius temperature.

Similarly, in GM-3 variety the yield was 3,700 kg per hectare under the elevated maximum temperature of one degree Celsius which increased to 3,850 kg per hectare under two degree Celsius temperatures. The normal yield was 3,550 kg per hectare. The yield went down to normal (3,550 kg per hectare) at four degree Celsius. The report says that gradual temperature reduction poses a negative impact on maize yield.

Production of rice

A study by the International Rice Research Institute showed that increases of 1Â?C at night during the growing season would reduce global rice yields by 10 per cent. Another global study showed that the production of rice and wheat could fall by eight per cent and 32 per cent respectively by the year 2050. In India, less water could cause a loss of up to 30 per cent of agricultural production, including food grains.

Rice crops are most vulnerable to global warming. Studies worldwide show that rising carbon dioxide levels may initially increase growth, but the benefit is temporary. Rising temperatures make rice spikelets - the slender branches containing rice flowers - sterile, and grain yields will fall.

Asia and sub-Saharan Africa will be amongst the most severely affected by climate change. About 90 per cent of the world's rice is grown and consumed in Asia (where 70 per cent of the world's poor live), and sub-Saharan Africa is the world's fastest growing rice consumer. The most vulnerable agricultural systems are the rain-fed uplands and lowlands that form almost 80 per cent of total rice land in Africa.

Other possible consequences

The possible adverse bearing of global warming on the output of other crops has still not been assessed or ascertained precisely, though this is believed to be relatively less. The kharif (summer) crops, in fact, may not be substantial losers in this respect.

On the positive side, the higher concentration of carbon dioxide in the atmosphere is expected to be beneficial for several crops. Also, the damage to the crops due to ground frost, which is quite common during the rabi season in the country's key north-western agricultural belt, may also reduce due to rise in temperature in the wake of climate change.

The issue of the impact of climate change on agriculture and the possible ways to cope with it were discussed at a recent meeting of the Parliamentary Consultative Committee attached to the Agriculture ministry. It points out that temperature rise and other anticipated atmospheric changes could reduce crop duration, increase crop respiration rate, affect equilibrium between crops and pests, lower fertiliser-use efficiency and increase evapo-transpiration. The net result of such changes would be that the water and fertiliser requirement of the crops would increase and the threat from pests and diseases would enhance. The decline of glaciers that sustain river flows could reduce the availability of water for irrigation and other purposes.

Besides, the rise in sea level and sea water temperature could adversely affect fisheries. Many of the precious coral reefs could vanish. Livestock could face heat stress, resulting in a decline in their productivity.

References

• Global warming behind crop losses by Nitin Sethi. The Times Of India, 05/04/2007.
• Climate change could trigger global food crisis by Ian Sample The Hindu, 01/09/2007.
• Global warming may hit maize, wheat production by Soumitra Trivedi. The Business Standard, 08/05/2007.
• Climate change may lead to 40% loss in food production by Surinder Sud. The Business Standard, 21/01/2008.
• Disaster round the corner, The Telegraph, 22/11/2007.
• Can crops be climate-proofed? by T.V. Padma. Science and Development Network, 11/01/2008.
• A Stitch in time by Surinder Sud, The Business Standard, Mumbai, 31 July 2007.