Observed and expected effects on so

Observed and expected effects on social systems

Further information: Effects of global warming#Social systems and Regional effects of global warming#Regional impacts
Vulnerability of human societies to climate change mainly lies in the effects of extreme weather events rather than gradual climate change.[158] Impacts of climate change so far include adverse effects on small islands,[159] adverse effects on indigenous populations in high-latitude areas,[160] and small but discernable effects on human health.[161] Over the 21st century, climate change is likely to adversely affect hundreds of millions of people through increased coastal flooding, reductions in water supplies, increased malnutrition and increased health impacts.[162] Most economic studies suggest that global warming would reduce world gross domestic product (GDP).[163][164]
Food security
See also: Climate change and agriculture
Under present trends, by 2030, maize production in Southern Africa could decrease by up to 30% while rice, millet and maize in South Asia could decrease by up to 10%.[165] By 2080, yields in developing countries could decrease by 10% to 25% on average while India could see a drop of 30% to 40%.[166] By 2100, while the population of three billion is expected to double, rice and maize yields in the tropics are expected to decrease by 20–40% because of higher temperatures without accounting for the decrease in yields as a result of soil moisture and water supplies stressed by rising temperatures.[14]
Future warming of around 3 °C (by 2100, relative to 1990–2000) could result in increased crop yields in mid- and high-latitude areas, but in low-latitude areas, yields could decline, increasing the risk of malnutrition.[159] A similar regional pattern of net benefits and costs could occur for economic (market-sector) effects.[161] Warming above 3 °C could result in crop yields falling in temperate regions, leading to a reduction in global food production.[167]
Habitat inundation
Further information: Effects of climate change on humans#Displacement/migration
See also: Climate refugee
In small islands and megadeltas, inundation as a result of sea level rise is expected to threaten vital infrastructure and human settlements.[168][169] This could lead to issues of homelessness in countries with low lying areas such as Bangladesh, as well as statelessness for populations in countries such as the Maldives and Tuvalu.[170]

Results (English) 2:

观察和对社会系统的进一步信息

预期效果：全球变暖#社会系统和全球变暖的影响#区域
脆弱的人类社会对气候变化的区域影响主要体现在极端天气事件的影响而不是渐进的气候变化的影响。[ 158 ]的气候变化的影响，到目前为止包括对小岛屿不良影响，[ 159 ]在高纬度地区的土著居民的不利影响，[ 160 ]和小但可辨别的对人类健康的影响。[ 161 ]在第二十一世纪，气候变化可能产生不利影响的数百万人通过增加沿海洪水，水的供应减少，增加营养不良和增加健康的影响。[ 162 ]最经济的研究表明，全球变暖将减少全球国内生产总值（GDP）。[ 163 ] [ 164 ]
食品安全
参见：气候变化和农业
在目前的趋势，到2030，在南部非洲的玉米产量减少了30%，大米，小米及南亚玉米可降低到10%。[ 165 ] 2080，在发展中国家，收益率可能会下降10%至25%，印度可以看到平均下降30%～40%。[ 166 ] 2100，而三十亿的人口预计将增加一倍，在热带地区，水稻和玉米产量预计将减少20–40%因为更高的温度而不降低会计收益率作为一个结果，土壤湿度和水的供应受气温上升。[ 14 ]
未来气候变暖的约3°C（2100，相对于1990–2000）可能导致在中纬度和高纬度地区的作物产量增加，但在低纬度地区，产量可能下降，增加营养不良的风险。[ 159 ]净收益和成本的类似的区域格局可能发生的经济（市场）的影响。[ 161 ]变暖3以上°C可能导致作物产量下降在温带地区，导致全球粮食产量减少。[ 167 ]
栖息地淹没
进一步的信息：气候变化对人类#位移/迁移
见效果：在小岛和大型三角洲气候难民
淹没，由于海平面上升将威胁到重要的基础设施和人居环境。[ 168 ] [ 169 ]，这可能导致在低洼地区的国家如孟加拉国无家可归问题，以及在如马尔代夫和图瓦卢国家人口无国籍。[ 170 ]