近地面臭氧、高温对中国粮食生产的影响

Effects of ground‑level ozone and high temperature on grain production in China

保障粮食安全是国家的重大战略,也是维护社会稳定的“压舱石”。由于同时面临着近地面臭氧浓度上升和极端气候等问题,中国的粮食生产可能受到臭氧和高温的双重不利影响。目前,国内外关于臭氧、温度分别对粮食产量影响的研究较多,但关于二者对粮食产量共同影响的研究较少。该研究从ECMWF的再分析数据中获取若干空气污染物和气候相关的变量,结合县级层面的水稻和玉米的投入产出和其他经济数据,构建了全国1747个县级行政区的面板数据,并首次运用半参数估计的方法估计了近地面臭氧和气温对水稻和玉米产量的非线性影响以及两者的联合影响。研究结果显示,高臭氧浓度和高温分别对水稻和玉米产量产生显著负面影响。其中,一元半参数估计结果显示,水稻产量对生长季的臭氧浓度(用体积分数表示)和气温的损失点分别为53×10^(-9)和19℃左右,而玉米产量的损失点则分别为60×10^(-9)和18℃左右。二元半参数估计结果显示,两种作物受到臭氧和高温的影响程度不同:水稻对于臭氧和高温都比较敏感,但玉米对高温的敏感程度高于臭氧。上述结论在经过大量的稳健性检验后依然保持稳健。在中国臭氧浓度逐年增长的背景下,一元半参数估计结果表明:在水稻和玉米种植区域将臭氧水平分别控制在65×10^(-9)和60×10^(-9)以内是减少粮食损失并兼顾臭氧污染治理成本的经济选择。同时,根据二元半参数估计结果可以得到以下启示:农业政策部门应充分考虑不同作物对于臭氧和高温的敏感程度的异质性,在其他条件允许的情况下指导农民通过种植结构的适应性调整,降低或消除臭氧对于粮食产量的负面影响。

Ensuring food security is a major strategic issue and a key to maintaining social stability for China.China’s grain production may be adversely affected by both ground-level ozone and high temperature due to the rise in ozone concentration and extreme weather.A large amount of literature has studied the effects of ground-level ozone and high temperature on crop yield separately,but very few of them have investigated the joint effects of these two factors on crop yield.We collected various types of air pollutants and climate-related variables from ECMWF reanalysis data.Combined with the input-output data and other economic data at the county level,a seven-year panel dataset with 1747 counties in China was constructed.This paper first used semiparametric estimation methods to estimate the separate and joint nonlinear impacts of ground-level ozone and high temperature on crop yield,respectively.Our results suggested that high ozone concentration and high temperature had significant adverse effects on rice and corn,respectively.The nonlin-ear estimation results showed that the critical loss points of rice to ozone and air temperature were about 53×10^(-9) and 19℃,while these numbers were approximately 60×10^(-9) and 18℃,respectively,for corn.The bivariate semi-parametric estimation results revealed that these two crops were affected by ozone and high temperature differently:rice was sensitive to both ozone and high temperature,but corn was more sensitive to high temperature than ozone.Empirical results remained robust after a series of robustness tests.Given that the background level of ozone in China has been increasing over the years,our nonlinear estimation results suggest that it is an economical choice to restrict the ozone levels to below 65×10^(-9) and 60×10^(-9),respectively,in rice-and corn-grown regions,balancing between grain loss and the cost of controlling ozone pollution.In addition,our binary semi-parametric estimation results suggest that the department of agriculture should fully consider the sensitivity heterogeneity of different crops to ozone and high temperature,and guide farmers to adapt via crop choices when other conditions permit to reduce or eliminate the negative impact of ozone on grain production.