# Modeling the Impact of Atmospheric Warming on Staple Crop Growth in China in the 1960s and 2000s
## 1 Introduction  
Under the influence of climate change and frequent extreme climate events, the photosynthetic production of crops faces great challenges [1]. To stabilize crop productivity and essentially ensure food security, it is thus necessary to make effective adjustments to agronomies depending on prediction of crop growth responses to climate change [2]. We need to assess the crop photosynthesis production response to climate change, on the one hand, in order to ensure food security in China [3], and on the other hand to increase the capacity for agroecosystems to manage atmospheric CO\({}_{2}\), thereby increasing carbon sink potential. Field observations and statistical data show that climate change, fertilization, irrigation and crop varieties in China have undergone significant changes in recent decades [4]. The climatic elements, e.g., temperature, precipitation, solar radiation and atmospheric CO\({}_{2}\) concentration all affect the photosynthetic production of crops to different degrees [4, 5, 6, 7, 8, 9]. From 1955 to 2000, the average annual maximum and minimum temperatures in China increased by 0.13 and 0.32 \({}^{\circ}\)C per decade, respectively [10]. In 1980, the rate of nitrogen fertilizer application for crop production was 9.4 Mt; it increased to 23.8 Mt by 2011 (National Bureau of Statistics, China, 2013). Meanwhile, the photosynthetic efficiency of leaf nitrogen, which reflects crop variety change, also showed a recognizable increase [3, 11]. To date, the effects of climate change on the photosynthetic production of crops in China have been widely evaluated with crop models, statistical analyses of historical data, field observations, satellite remote sensing data and other methods [4; 7; 8; 9; 12; 13]. In different regions, the effects of climate warming on crop productivity of China vary greatly, resulting in changing growth periods and spatial moving of different rotation systems [14], such as the southward shift of the northern limit of the double-cropping system and the northward shift of the northern limit of the triple-cropping system [15]. The modelling approaches have been applied to simulate crop photosynthesis production at different spatial scales, including at field [6; 16; 17], regional [5; 18; 19; 20; 21], national [6; 22; 23] and global scales [24]. The impacts of climate change on crop productivity, growth periods and planting systems have also been assessed with the models. Taking data for the period of 1984-2003 from the China Rural Statistical Yearbook of the National Bureau of Statistics and observations of annual average temperature for the same period, [PERSON] and [PERSON] [25] concluded that climate change, characterized by temperature increases, has a pronounced positive effect on crop production in Northeast China, but negative effects in North, Northwest and Southwest China. Warming prolongs the growing period of crops in the cold regions with poor thermal conditions, which is beneficial to crop variety selection and planting structure adjustment. It is unfavorable for crops with short growth periods, as warming accelerates their growth rate and shortens their growth period. For a 1 \({}^{\circ}\)C increase in the average temperature during the crop growth period, the rice growth period is shortened by 7-8 days, while that of winter wheat is shortened by 17 days, which is not beneficial for the accumulation of crop dry matter. Warming thus accelerates crop growth and shortens the growth period, ultimately leading to decreased crop production [26]. Below the optimum temperature of crops, which is usually the case in temperate regions such as China, increasing temperature stimulates both crop photosynthesis and respiration that contribute contradictorily to the accumulation of carbon for crop growth. When the increment of photosynthesis by warming is larger than that of respiration, crop growth will benefit from the temperature increase; otherwise, there will be a reduction in crop productivity.