Background
Noting that climate alarmists claim that global warming increases "the frequency and severity of extreme temperature events that lead to declining crop yields," the authors acknowledge that extreme temperatures are indeed "destructive to rice growth and, hence, critical to development of rice productivity (Yoshida, 1981; Farrell et al., 2001)," adding that seeding, booting and heading-flowering are "the most vulnerable periods to extreme temperatures throughout the life cycle of rice plants," citing Nishiyama (1976) and Wang et al. (2009) in this regard.

What was done
Sun and Huang, as they describe it, examined "changes in extreme temperature stress over the past five decades [1961-2008] by quantifying the indices of temperature stress during different growth stages of irrigated rice across mainland China."

What was learned
The two researchers demonstrated, first of all, that the indices of low- or high-temperature stress can indeed be used to explain the year-to-year changes in rice yield. And their further analyses indicated that "low-temperature stress in the seedling and heading-flowering stages of single[-crop] rice in northeast China, the seedling stage of early rice and the heading-flowering stage of late rice in the double[-crop] rice regions has reduced [i.e., declined] over the period of 1961-2008," while "no significant trends in low-temperature stress were detected during the booting stage." At the other end of the temperature spectrum, they found that "global warming did not enhance high-temperature stress in the heading-flowering stage over the same period, except in early rice in the mid-lower Yangtze River valley, where the high-temperature stress in the 2000s was higher than in previous decades."

What it means
As stated in the title of the Chinese scientists' paper, "global warming over the period 1961-2008 did not increase high-temperature stress," but it "did reduce low-temperature stress in irrigated rice across China," which made the warming of that period a net positive influence on irrigated rice production across the country.

References
Farrell, T.C., Williams, R.L. and Fukai, S. 2001. The cost of low temperature to the NSW rice industry. In: Proceedings of the 10th Australian Agronomy Conference, Hobart, Australia, 28 January-1 February.

Nishiyama, I. 1976. Effects of temperature on the vegetative growth of rice plants. In: Climate and Rice. International Rice Research Institute, Los Baņos, Philippines, pp. 159-186.

Wang, S.W., Ma, S.Q., Chen, L., Wang, Q. and Huang, J.B. 2009. Chilling Injury of Crops. China Meteorological Press, Beijing, China.

Yoshida, S. 1981. Fundamentals of Rice Crop Science. International Rice Research Institute, Los Baņos, Philippines.