一份报告说，到2080年，气候变化造成的农业生产力丧失可能导致有100万到700万成年墨西哥人移民到美国。Michael Oppenheimer及其同事使用1995年到2005年的墨西哥移民、作物产量和气候数据估计了作物产量对墨西哥人移民美国的影响。这组科学家的方法把气候引起的移民从同样可能影响移民决定的其他经济和政策因素中分离了出来。
这组作者报告说，根据农业进步是否会帮助农民适应更炎热干燥的气候，至多10%的墨西哥成年人（即大约670万人）可能在未来70年里仅仅因为农业生产力的衰退而移民美国。这组作者指出，尽管这一分析取决于被研究的时期内墨西哥特有的因素，诸如墨西哥和美国之间的相对经济稳定性，研究结果提示，大批人——特别是在发展中国家——可能由于气候变化引起的农业压力而移民到其他国家。(生物谷Bioon.com)
生物谷推荐原文出处：
PNAS doi:10.1073/pnas.1002632107
Linkages among climate change, crop yields and Mexico–US cross-border migration
Shuaizhang Fenga,b, Alan B. Kruegera,c,d, and Michael Oppenheimera,e,1
a Woodrow Wilson School of Public and International Affairs, Princeton University, Princeton, NJ 08544;
b School of Economics, Shanghai University of Finance and Economics, Shanghai 200433, China;
Departments of c Economics and
eGeosciences, Princeton University, Princeton, NJ 08544; and
dUS Department of Treasury, Washington, DC 20220
Climate change is expected to cause mass human migration, including immigration across international borders. This study quantitatively examines the linkages among variations in climate, agricultural yields, and people's migration responses by using an instrumental variables approach. Our method allows us to identify the relationship between crop yields and migration without explicitly controlling for all other confounding factors. Using state-level data from Mexico, we find a significant effect of climate-driven changes in crop yields on the rate of emigration to the United States. The estimated semielasticity of emigration with respect to crop yields is approximately ?0.2, i.e., a 10% reduction in crop yields would lead an additional 2% of the population to emigrate. We then use the estimated semielasticity to explore the potential magnitude of future emigration. Depending on the warming scenarios used and adaptation levels assumed, with other factors held constant, by approximately the year 2080, climate change is estimated to induce 1.4 to 6.7 million adult Mexicans (or 2% to 10% of the current population aged 15–65 y) to emigrate as a result of declines in agricultural productivity alone. Although the results cannot be mechanically extrapolated to other areas and time periods, our findings are significant from a global perspective given that many regions, especially developing countries, are expected to experience significant declines in agricultural yields as a result of projected warming.
