氣候條件對全球糧食作物生產影響──縱橫資料模型的應用

The Effects of Climate on the Global Corn and Wheat Production-An Application for Panel Data Model

研究文獻顯示氣候變遷會影響糧食作物之生產，進一步對全球糧食供給造成衝擊，但未考量到氣候條件門檻對作物產量的影響。本研究為探討氣候變遷及其門檻對作物產量之影響，以糧食作物玉米及小麥為實證案例，分別探討氣候條件包括氣溫、乾旱指數、濕度指數對作物產量之影響。本研究應用縱橫資料模型（panel data model）與縱橫資料門檻模型（panel threshold model）進行實證分析，首先為應用縱橫資料模型估計各氣候條件對作物產量的影響，接著再以縱橫資料門檻模型探討玉米產量、小麥產量與氣溫間之非線性關係，並以氣溫為門檻變數，進一步觀察在不同溫度門檻下，各氣候因素對作物產量之影響。
實證結果顯示乾旱指數和玉米、小麥產量為正向之關係，亦即在越不乾旱之氣候條件下越有利於玉米和小麥的生產；而濕度指數對於兩者產量則有負面之影響，亦即產季之氣候越潮濕越不利於玉米和小麥的生產；氣溫對於兩者產量亦為負面之影響，亦即溫度越高越不利於玉米和小麥之生產。此外，氣溫對於玉米產量之影響存在三個門檻溫度，而氣溫對於小麥產量之影響則存在單一門檻溫度，且氣候條件在不同之溫度區間對玉米和小麥產量有著不同程度的影響。

Many literatures have found that climate change has made significantly impacts on global supply for food crops but did not take the climate threshold into the consideration. In order to analysis the effects of climate threshold on the global food production, the effects of climate conditions including temperature, PDSI, and humidity on global corn and wheat production is estimated. We firstly apply panel data model to estimate the relationships between the production of crops and climate conditions. Furthermore, in order to observe the relationships between the crop production and climate conditions in different temperature regimes, a panel threshold model with the temperature threshold is applied. The empirical results indicate that the positive relationship between PDSI and production of corn and wheat is found which explains a negative effect on production due to the severity droughts. The negative relationship between relative humidity and production for corn and wheat is also found which indicate that the higher humidity is harmful to production. Similarly, the negative relationship between temperature and production for corn and wheat is estimated which shows the higher temperature will have a negative impact on corn and wheat production. However, such effect of temperature on crop production is not fixed and will depend on the level of temperature. The empirical results show that three temperature thresholds for corn and one temperature threshold for wheat is found which implies that the effects of temperature on crop production need to take the threshold into consideration.