The impact of projected global warming on crop yields has been
evaluated by indirect methods using simulation models. Direct
studies on the effects of observed climate change on crop growth
and yield could provide more accurate information for assessing
the impact of climate change on crop production. We analyzed
weather data at the International Rice Research Institute Farm from
1979 to 2003 to examine temperature trends and the relationship
between rice yield and temperature by using data from irrigated
field experiments conducted at the International Rice Research
Institute Farm from 1992 to 2003. Here we report that annual mean
maximum and minimum temperatures have increased by 0.35°C
and 1.13°C, respectively, for the period 1979–2003 and a close
linkage between rice grain yield and mean minimum temperature
during the dry cropping season (January to April). Grain yield
declined by 10% for each 1°C increase in growing-season minimum
temperature in the dry season, whereas the effect of maximum
temperature on crop yield was insignificant. This report provides a
direct evidence of decreased rice yields from increased nighttime
temperature associated with global warming.