today's scenario

 The ‘green revolution’ and industrialisation of agriculture led to huge increases in crop production around the world. 

The ‘green revolution’ which combined (i) breeding of high-yielding varieties, (ii) the application of fertlilisers and pesticides, (iii) the increased use of irrigation and (iv) cheap transport fuels, led to huge increases in food crop production in the period since the Second World War. Global cereal production has increased three-fold per hectare and in developed countries using energy-intensive agricultural systems, yields of some crops have increased 5 or 10-fold per unit of land.

But what of the future? The IPCC in 2007 assumed global crop yield increases of 80% by 2050, continuing the trend of the post war era. But such increases in yields of some crops have already ceased. Yields of wheat have plateaued and while some gains continue to be made in maize and rice productivity, it is sobering to note that Chinese rice production only increased by 2% per hectare in the period 1997 to 2007 while in the preceding decade it increased by 17% (FAO 2009). 

Optimists point to the positive effects of increased temperatures and atmospheric CO2levels on crop productivity in the future. While it is true that increasing the temperature and CO2 levels can increase plant productivity in some specific cases (depending on the type of plant and the place), the widely held view among plant physiologists is that any such benefits will be small, and will be outweighed by the negative impacts of higher temperatures, water limitations and extreme weather events (Ainsworth and Ort 2010; Long and Ort, 2010). Growing-season temperatures may be higher than the average (e.g.. a 3oC average rise could be 4oC in summer and 2oC in winter). 

World agriculture consumes about 100 million tonnes of nitrogen fertilisers per year. Most of this fertiliser is manufactured from natural gas by means of the Haber-Bosch process. The methane (CH4) of natural gas is oxidised to CO2 and hydrogen. The hydrogen is then reacted with nitrogen from the air at high temperature and pressure to form ammonia. This process consumes as much as 5% of the world’s natural gas production. And it puts at least 300 million tonnes of CO2 into the atmosphere every year. Eutrophication, soil acidification and emission of the greenhouse gases nitrous oxide and methane are other consequences of nitrogen fertiliser use.