Jennifer Burney of the School of International Relations and Pacific n Studies and V Ramanathan of the Scripps Institute of Oceanography, both from the University of California, San Diego, la Jolla, in a paper published in the proceedings of the National Academy of Sciences, USA (2014), stated, “Ever since the Green Revolution first staved off famines in the 1960s, Indian rice and wheat systems have grown over the past half century to play critical roles in the world food economy.” China, India and the US are the top producers of wheat (FAO, 2009).The Indo-Gangetic plains produce approximately 15 per cent of the world’s wheat crop. Global food security is tightly linked with India’s rice and wheat production.
Rodomiro Oritz, and a group of scientists from CIMMYT, Mexico, (the Institution, which developed the high yielding wheat varieties, resulting in Green Revolution in India), reported from their studies on effects of climate change on wheat yield (2008), that by 2050, climate changes will cause reclassification of the Indo-Gangetic plains from a favourable, high-potential wheat production environment to a heat-stressed, short-season production environment.
Recent research shows that climate change has a negative effect on agricultural production all over the world, including India. The factors that will primarily affect crop production in the coming decades are: Rising temperature, an intensified hydrological cycle and increasing concentration of carbon dioxide (the major greenhouse gas, GHG) in the atmosphere.
Model projections by 2050 AD indicate that continental level averages of seasonal precipitation will vary between minus (-) 20 per cent to plus (+) 10 per cent. The clearest consequence of greenhouse gas emissions is increase in precipitation in high latitudes and decrease in subtropical areas. In other regions, most models do not predict larger changes in precipitation relative to natural variability, even by 2100 AD (Tebaldi and co-researchers, 2011).
Higher carbon dioxide levels in the atmosphere increase growth and yield, mainly through their effect on the crop’s photosynthetic processes.
Higher temperature causes faster crop development and shorter crop duration, which in most cases is associated with lower crop yield. The rates of warming in most climate models are roughly linear for the 1980 to 2050 AD period, both at global and regional scales (Solomon and co-researchers, 2007).
In the past several decades, air temperatures have been warming in most of the major cereal cropping regions around the world. Average global increase in maximum temperature (Tmax) from 1980 -2011AD is roughly 0.3°C per decade and minimum temperature (Tmin), 0.2°C per decade (Sacks and co-researchers, 2010).
According to David B lobell and Sharon M Gourdji (2012) of Stanford University, USA, ‘Over the next few decades the carbon dioxide trends will likely increase global yields of crops roughly by 1.8 per cent for every decade and warming trends will reduce global yield by 1.5 per cent per decade’.
Research studies have indicated that wheat yield decrease by 5-10 per cent for every one degree (C) rise in mean seasonal temperature. As temperature increases, yields of cereals decrease due to shortening of grain filling period. For many annual crops, a brief spell for 1-3 days of higher temperature (higher than 32-36 C) at the flowering time will greatly reduce seed set and hence crop yield.
US maize and soybean yields are predicted to decrease by 30 per cent to 46 per cent before the end of the century (Schlenker and Roberts, 2009).
Climate change has been identified as a very serious environmental problem for South Asia, with particularly high vulnerability being noted for the agricultural sector (lal, 2001). Even a small change in climate may result in high social vulnerability, for at least two reasons: one, Many crops rely on the regular return of monsoon rainfall, a system that has fluctuated widely in the past, (Krishna Kumar, 2004); two, The economic potential to adapt is very low for most of Indian farmers.
An Indian specific study indicates that June-September rainfall and October-November minimum temperatures have significant influence on rice yield. Higher rainfall ensures both larger areas to be cultivated and higher yield. Higher night time temperatures reduce yield (Auffhammer and co-researchers, 2006).
S A Saseendranand co-researchers (2000) used CRES-Ricev3 crop simulation model and created a scenario of Kerala for the decade 2040-49 AD. The model predicted carbon dioxide concentration of 460 ppm, an increase in surface temperature during the monsoon season by 1.5 C, and rainfall increase by 2 mm per day. Further, it projected that maturity period of rice would shorten by 8 per cent but yield would increase by 12 per cent. The positive effect of increase in carbon dioxide concentration would neutralise adverse effect of temperature rise. This is not likely to be the scenario in other rice growing States, especially in northern and western India, where rainfall pattern and temperature in the monsoon season are different.
Based on statistical crop models, lobell and co-researchers (2008) reported that, crops most likely to be negatively affected by climate change globally would be wheat and rice in southeast Asia, maize in southern Africa, millet, groundnut, and rapeseed (Brassica napus) in southern Asia and sorghum (Sorghum bicolor) in Sahel. Since climate change is going to change the cropping seasons, agriculture has to adapt to such change.
This will include, (i) Adjustment of planting and harvest times - Crops may have to be planted and harvested early/late commensurate with changes in seasonal temperature and rainfall pattern
(ii) Expansion of croplands to more permissive areas - The crop varieties now grown may no more be suitable to the existing areas. They have to be shifted to higher latitudes/altitudes with cooler climate, suitable rainfall pattern and day length
(iii) Changing genotypes or species to those with more appropriate thermal time or heat stress tolerance - Crops/ crop varieties have to be selected, which can tolerate longer thermal time and have tolerance to heat stress. This may involve changing the cropping pattern.
(iv) Developing new germplasm with improved traits - New crop varieties have to be developed, which can give higher yield under altered climatic conditions
(v) Altering fertilisation rates and irrigation practices - New field trials have to be conducted to fix fertiliser rates and irrigation schedule for new crop varieties and the changed cropping season and
(vi) More accurate climate forecasting to reduce production risks.
Though the tasks as enumerated above appear to be formidable, these can be achieved by the agricultural scientists, who developed the existing crop varieties, cropping sequences and crop husbandry practices and maximized crop production under all types of climatic conditions around the globe.
(Dr Mitra is a former Dean, College of Agriculture, OUAT. This is a research based article. References cited can be accessed through internet for more information. Email: gnmitra@gmail.com)