1979—2017年北极陆地气候变化趋势

北极地区是受全球变暖影响最为显著的地区之一。北极升温速率超过全球平均速率的2倍,这一“极地放大现象”和海冰的快速消融不仅造成当地环境的剧烈变化,还深刻影响着中纬度的天气和气候系统。深入理解气候长期趋势的季节和地理分布特征,有助于应对北极气候变化及其影响,并为未来开发北极资源服务。考虑到北极地区观测台站稀疏带来的不确定性,本文利用多套格点化的观测分析和ERA-Interim再分析资料,结合线性趋势分析,研究了1979—2017年60°N以北陆地地表温度、降水、气温日较差、年较差及相关极端气候指标的变化趋势。结果显示：①各资料中气温变化的一致性很高,但对于降水在2008年之后的变化,不同资料差异较大,可能是金融危机下可用台站数量急剧下降造成的。②ERA-Interim再分析资料能够很好地再现北极陆地温度和降水的整体增加趋势,变化速率分别约（0.57±0.07） ℃/10 a和（0.10±0.05） mm/d/100 a。春、秋、冬季升温趋势强,而夏季升温趋势较弱。北冰洋沿岸地区升温速率最大,局地可超过1.0 ℃/10 a。③降水的增加趋势在秋季最大。西伯利亚降水的增加与局地升温有很好的对应关系,其中秋季西伯利亚东部平均和极端降水的增加趋势可达热力学约束的8 %/K。④夏季气温日较差没有显著的变化趋势,春季阿拉斯加和加拿大北部地区的气温日较差呈显著增大趋势,其他区域则以减小趋势为主。气温年较差在北欧、阿拉斯加和加拿大北部呈减小趋势,在西伯利亚西部和东部呈增加趋势。无论冬夏,温度最小值的升高趋势比最大值更显著;冬季温度最小值的升高趋势比夏季更显著。研究表明,地表升温是北极陆地局地降水增加的重要驱动因素,不同区域降水变化的差异则可能与环流变化有关;观测台站数量的减少对降水趋势的监测有显著影响;ERA-Interim可作为北极地区观测分析资料的重要补充,特别在台站稀疏地区和台站数量减少的时段,ERA-Interim可提供一致和可信的气候变化信息。

Climate changes over the Arctic land during 1979-2017

The Arctic is one of the rapidly changing regions remarkably influenced by global warming. Polar warming amplification (warming rate two times larger than the global mean) and rapidly declining sea ice lead to not only dramatic changes in the local environment, but also profound effects on weather and climate system in the mid-latitude. An in-depth understanding of seasonal and geographical features of long-term trends can contribute to policy responses to climate change and its consequence, supporting Arctic resource development in the future. Using gridded observational analysis datasets and the ERA-Interim reanalysis, this study focused on linear trends of surface air temperature, precipitation, and related extreme indices in the land area north of 60°N during 1979-2017. The results show that temperature changes highly agree with each other while precipitation changes are distinct across the multiple data sources, especially after 2008, which is possibly caused by sharply decreased gauges in use under the global financial crisis. The ERA-Interim dataset can well reproduce the upward trends of near-surface air temperature and precipitation over the Arctic land, about (0.57±0.07) ℃/10 a and (0.10±0.05) mm/d/100 a for annual mean. The warming trend is strong in spring, autumn, and winter whereas weak in summer. Areas near the Arctic coasts have the largest warming rate, with local warming higher than 1.0 ℃/10 a. The increasing trend of precipitation in autumn is the largest. The precipitation increases in Siberia are well linked to the local surface warming. During autumn, increases in both the mean and extreme precipitation in eastern Siberia can be as high as the thermodynamically constrained 8 %/K. No evident trend of diurnal temperature range is observed in summer. In spring, the diurnal temperature range in Alaska and northern Canada increases evidently whereas a decreasing trend emerges in other regions. Annual temperature range decreases in the Nordic, Alaska, and northern Canada while increases in western and eastern Siberia. In both winter and summer, warming trend of minimum temperature over the Arctic is larger than that of maximum temperature, which is also larger in winter than in summer. This study evidences that surface warming is an important driver of local precipitation increase over the Arctic land while circulation changes may create the geographical differences; decrease of observational stations has an obviously negative impact on monitoring the long-term trend of precipitation; ERA-Interim is an important alternative to observational analysis data in the Arctic land. Especially for regions with sparse weather stations and for periods when the number of available stations decreases, the ERA-Interim data can provide consistent and reliable climate change information.