Global warming and its devastating effects has been a burning issue that is raising concern among the scientific community. Global warming, the rise in the global ambient temperature is expected to cause a catastrophic change in the entire global climate and thereby threatens the very existence of the biosphere in earth. Accelerated level of green house gases in the earth’s atmosphere is the sole cause of the problem. Although, natural sources account for a significant amount of these gases, anthropogenic causes are the prime factors behind the exceeding concentrations.

Being the most climate dependant human activity, agriculture is certainly going to face a serious decline within this century due to global warming unless the emissions of carbon dioxide and other green house gases are reduced. Estimations based on several climate models have shown that the overall impact of baseline global warming by 2080s will be a reduction in agricultural productivity by 16% without carbon fertilization and 13% with carbon fertilization. However, it is very complex to describe the phenomena as many factors like temperature, rainfall pattern, crop tolerance, carbon dioxide concentration, etc are adhered to it.

Global warming affects agricultural productivity by the following processes: Change in climatic parameters like precipitation pattern and temperature regime, change in the carbon dioxide level, change in the hydrological make-up of an area and increased attack of pest and diseases. Increased variation in frequency, intensity and pattern of rainfall result in alteration of the patterns of drought and deluges. This can lead to reduction of crop yield. Elevated range of temperatures has been found to alter the monsoonal climate across the globe. Again changes in temperature regime can be corelated with reduced availability of water in soil for the crops. Elevated temperature also accelerates the crop development phases. These two are also combined with alteration of various physiological activities of plants with a combined negative affect on crop productivity.

Unlike temperature and precipitation, elevated level of carbon dioxide has a dual effect on crop productivity. Some plant scientists believe that elevated level of this green house gas may be beneficial due to its positive effect on photosynthesis, especially in case of plants like rice, wheat, etc. On the other hand, it is also important that at higher temperature condition, the beneficial effect of elevated level of carbon dioxide will be negated by high temperature. Another important point is that excessive vegetative growth under elevated carbon dioxide condition can also lead to decreased formation of grain forming biomass resulting in lower productivity.

Change in the temperature regime as well as rainfall pattern also causes change in the hydrological make-up of an area. The number of floods may rise due to ice melting, cloud burst, etc while drought can also increase due to altered rainfall pattern. Increase in the frequency of lean flows due to droughts will also result in reduced water availability for crops. Crop quality also changes due to increased temperature and higher carbon dioxide level.

Another important aspect related to declining agricultural productivity is the incidence of newer pest and diseases in crops. It has been speculated that newer pest and disease causing pathogens will be introduced to newer areas due to altered climatic pattern. Again, under high temperature and high humidity condition, intensity of fungal diseases and pest attack will be aggravated resulting in decreased yield of crops. Weed infestation will also be higher under such conditions.

Around the globe, agricultural productivity will vary in countries depending on their location, economic condition and numerous other factors. Significant losses will be observed in countries located nearer to the equator where temperature can easily reach beyond crop tolerance levels. An overall decline of three to five per cent in production of world’s six main staple crops — wheat, rice, corn, soybean, barley and sorghum — is predicted by scientists for a rise of 10C in the ambient temperature. As a country that mostly practises rainfed agriculture, India will certainly be affected by global warming and climate change. Predictions from climate model in India expect a change of surface air temperature of 20C to 50C with a broad south to north gradient. Coastal regions of the country will face a serious threat to its agriculture and allied sectors due to climate change and global warming. Increased salinity in the coastal regions arising from sea level rises and in the interior from the change in the water table will also hamper the process of agriculture activities in the country. Another fact related with the water availability in the country is that Himalayan Glaciers that are the source of dry season water in the country has started disappearing at a much faster rate within the last 50 years.

Under these circumstances the challenges coming to the global community is to develop newer and improved technologies that can adapt to the newer climate. Improvement of crop varieties in terms of temperature tolerance, drought and flood tolerance, photoperiod insensitivity, etc is required. Improvements in irrigation as well as drainage in the agriculture areas are also needed. Development of crop varieties that might cope better with the changed climate is also a challenge in such condition. Another important point in this regard is the exploration of the potential crops or crop varieties that can utilize higher level of carbon dioxide to the maximum extent.

Manoshi Goswami