Field studies conducted by the IRRI confirm predictions about theoretical studies that global warming will make rice crops less productive. The IRRI combine 25 years of collated data with yield trends to discover that simulation models underestimated the effects of global warming on rice crops by half because warmer overnight temperatures had been overlooked.
The study suggests that while higher night time temperatures are likely to have a sustained effect on rice production, higher day time temperatures are not likely to have much impact on yields at all.
The IRRI says that its models show that for every 1¢ªC rise in temperature rice yields declined by 15 per cent. With world temperatures predicted to increase by 1.5 to 4¢ªC, this suggests that hard-won productivity gains in rice production aimed at feeding rising populations could be lost.
¡°Most studies of temperature and global warming effects on crop growth and grain yield are based on daily mean air temperature, which assumes no difference in the influence of day versus night temperature,¡± wrote the nine-member research team from IRRI, China and the United States led by IRRI crop physiologist Shaobing Peng. ¡°This report provides direct evidence of decreased rice yields from increased night temperature associated with global warming.¡±
Unless a solution is developed this could spell big problems for the Asian region, where 90 per cent of all rice is grown and consumed and more than 2 billion people obtain 60 to 70 per cent of their calories from the staple. Furthermore more than half of the worlds 1.3 billion poor are Asian farmers and consumers, who can spend up to 40 per cent of their annual income on rice.
In recent months poor rice harvests in China have had a significant impact on prices in the country, where many producers and food manufacturers are struggling to source enough rice to meet demands. In turn as rice stocks diminish, prices are rapidly rising, contributing to the increasing instability of the economy there.
However the most recent crop failings have largely been caused by inclement weather conditions and the indications are that this year¡¯s crop is likely to replenish stocks. On the other hand the effects of global warming on rice crops are likely to have a far more long-term and permanent effect on the industry.
¡°The results of this study highlight the need for greater fundamental understanding of the effects of night temperature on physiological processes governing crop growth and yield development,¡± concluded the authors of Rice yields declining with higher night temperatures from global warming. Dr. Peng added, ¡°The challenges now is to get the financial resources needed to develop new rice varieties that can still yield well despite any increase in temperatures in rice growing areas.¡±