氣候衝擊與農家在氣候變遷下的調適策略

Abstract

農民是最接近自然環境且最易受到氣候變遷影響的職業，而與歷史氣候條件相比的氣候變化可以視為對農民生產時的一種衝擊。透過結合臺灣蔬菜農家的特性資料與詳細的歷史氣候資訊，利用多種計量經濟學方法，本篇論文探討了氣候衝擊對農民調適策略的影響、經濟效果與福利分析。 於第二章節中，本研究探討了氣候衝擊對農家的三種調適決策之影響，包括勞動分配、溫室設施以及有機農法。為了解決空間自相關及方程間干擾相關的問題，此研究採用了空間似無關迴歸（Spatial Seemingly Unrelated Regressions, SSUR）方法。利用2015年農業普查中普查數據及歷史氣溫與雨量數據，我們的研究發現顯示，正向和負向的氣候衝擊影響具有不對稱性，尤其是雨量增加的衝擊提高了農家中從事非農業工作人口比例和有機農法的採用，而乾旱衝擊則未顯示顯著影響。同時，溫度升高會使溫室設施的比例增加。我們還觀察到，經驗會調節降雨衝擊帶來的影響。此外，研究中亦考量到不同農家類型的異質性效果。從針對特定農戶群體的分析發現，高齡農戶在勞動分配上的反應比其他群體更強，而微型農戶的行為則較不易因氣候衝擊而有所改變，顯示不同特性的農家對於氣候衝擊的敏感度與應對能力有所差異。 於第三章節中，研究主軸聚焦在蔬菜農家的三種氣候調適行為—勞動分配、溫室設施使用以及有機農法—的經濟效果，考量到農民有同時採用多種策略的情況，故而從採用、調適強度、調適策略的組合依次進行分析。本研究透過Probit二階最小平方工具變數法（probit two-stage least squares instrumental variable method）及多項處理效果模型（multinomial treatment effect model），從結果發現採用任一策略的經濟效果為負，然在採用強度上，相較於僅採用某一種策略，採用任兩種策略的經濟效果為負，但採用三種策略帶來了正向的經濟表現，代表著各種策略對於經濟表現的影響極為不同。而細分各種策略的組合，在非農勞動分配、有機採用的策略下，雖然其單獨的經濟效益不佳，但與溫室一同利用的組合策略都帶來了正向的效益。這些對於經濟效果的分析，提供了策略間的組合建議，尤其是溫室與有機的同時採用，溫室設施能夠大程度彌補有機可能帶來的減產影響，代表某些調適策略間有互補並提升效益的效果。 在第四章中，本研究利用2010年和2015年的農業普查數據，以蔬菜農戶為研究對象，從農民福利的角度出發，分析氣候變遷調適策略如何影響農民的經濟表現與收入不均問題。首先，利用Binder-Oaxaca 分解的方式，將農民經濟表現的進步分解為稟賦差異及係數改變的影響，結果顯示農民在溫室設施及有機農法採用的改變上都造成了農民經濟表現的進步，然而卻是因為可帶來效益的溫室設施採用增加，以及對收益是負向效果的有機農法採用減少。而在收入不均度上，資料中農民的收入變異隨著時間減少，透過迴歸分解（regression decomposition）的結果表明，溫室的採用擴大了不均度，而有機農法卻縮小了不均度。同時，本研究也針對另一種收入不均度—基尼係數（Gini coefficient）來衡量，兩種策略對於收入不均度的影響方向仍得到一樣的結果。這些結果代表溫室的採用雖可帶來經濟效益，但其對於資金或是技術的門檻可能將其效益聚攏在收入較高的農家，使得農家收入分配更加不平等，在政策上更加需要對於資金受限的小農提供財務與技術上的支援。

Farmers are the profession most closely connected to the natural environment and are also the most vulnerable to the impacts of climate change. Compared to historical climate conditions, climate change can be seen as a shock to the production of farm households. This thesis is composed of three essays that explore the impact of weather shocks on farmers' adaptation strategies, the economic outcomes following adaptation, and the welfare implications, by combining detailed data on vegetable farm households in Taiwan with historical climate information, employing various econometric methods. In Chapter 2, this study investigates the impact of weather shocks on three adaptation strategies by farmers: labor allocation, greenhouse facilities, and organic farming. To address spatial autocorrelation and correlated disturbances among the strategies, this research adopts the spatial seemingly unrelated regression (SSUR) method. By utilizing the 2015 agriculture census along with historical temperature and rainfall data, the findings reveal that the effects of positive and negative weather shocks are asymmetric. Specifically, the shock of increased rainfall raised the proportion of the population engaged in non-agricultural work and the adoption of organic farming, while dryer shocks did not show any significant effects. Additionally, it is found that higher temperatures led to an increase in the use of greenhouse facilities. This study also observes the moderation effect of past shock experiences on the impact of rainfall shocks. Moreover, considering heterogeneous effects across different types of households, it is found that elderly farms respond more strongly to labor allocation changes than other groups, while mini farmers show less change in behaviors due to weather shocks, indicating that farmers with different characteristics have varying coping capacities and responses under climate change. The focus of Chapter 3 is the economic effects of the three climate adaptation strategies on vegetable farm households. Since farmers may adopt multiple strategies simultaneously, the analyses are conducted in sequence as the impacts of adaptation on farm profitability, the outcomes of differing adaptation intensity, and portfolio. Using the probit 2SLS IV method and multinomial treatment effect model, the results indicate that adopting a focused or non-diversified portfolio results in negative economic effects. However, while two adaptation strategies are adopted, the economic effect is negative relative to adopting only one strategy; adopting all three strategies leads to higher economic performance. This suggests that the impact of adaptation strategies on economic performance varies significantly with the intensity. In the cases of adopting only non-agricultural labor allocation or organic adoption strategies, the economic effects are negative. However, the combinations of either strategy with greenhouse facilities lead to higher profitability. These analyses provide important inferences for the efficient combination of strategies, especially the simultaneous adoption of greenhouse and organic farming, since the use of greenhouse facilities can greatly offset the potential yield reduction from organic farming. The result indicates the complementary relationship between certain adaptation strategies that enhance adaptation benefits in terms of farm profitability. In Chapter 4, this study uses two waves of agriculture census data, 2010 and 2015, to analyze the impacts of climate change adaptation strategies on farmers' income dynamics and inequality among farm households from the perspective of welfare implications. First, by applying the Binder-Oaxaca decomposition method, the improvement in farmers' economic performance is decomposed into the endowment effect and coefficient effect. The results show that changes in the adoption of greenhouse facilities and organic farming led to improvements in farmers' economic performance, which was primarily due to the increasing adoption of greenhouse facilities which provide benefits, while the negative effects of adoption of organic farming were reduced. As for income inequality, the variation in farm sales revenue decreased from 2010 to 2015. Results from regression decomposition suggest that the adoption of greenhouse facilities enlarges income inequality, whereas organic farming reduces it. Additionally, this study also presents the results using a different income inequality index, the Gini coefficient. The direction of the impact of the two adaptation strategies on income inequality remains consistent. These findings indicate that while the adoption of greenhouses may bring economic benefits, the financial or technical barriers may concentrate the benefits among wealthier farmers, exacerbating income inequality among farmers. This result suggests that governmental policies should focus on providing financial and technical support to small-scale farms with limited resources.