过去千年北半球中高纬夏季温度多年代际变化的归因分析

THE ATTRIBUTION OF THE EXTRATROPICAL NORTHERN HEMISPHERE SUMMER TEMPERATURE MULTIDECADAL VARIABILITY OVER THE LAST MILLENNIUM

在过去千年背景下评估自然和人为因素对北半球温度的影响程度,有助于辨识不同特征时期(如:中世纪气候异常期、小冰期和现代暖期)北半球温度的演变机制,对预测未来气候变化有重要参考意义。文章基于多元回归模型尝试量化了过去千年(870~1992年)自然因素(火山活动、太阳活动、地球轨道参数变化)、人为因素(温室气体浓度、大气气溶胶浓度、土地利用变化)、内部变率(北大西洋和北太平洋海表温度在多年代际上的内部变率部分,分别简称为AMO和PMO)对北半球中高纬度地区(30°~70°N)夏季温度的贡献。结果表明:在多年代际(>30年)时间尺度上,这些因子可以解释约73%的北半球夏季温度变化方差。在中世纪气候异常期(Medieval Climate Anomaly,简称MCA;900~1100年),AMO和PMO等内部变率可能对北半球温度变化起了重要作用;在小冰期(Little Ice Age,简称LIA;1450~1850年),火山活动是北半球夏季温度最重要的驱动因素;1851年以来,人类活动的贡献最大,接近50%,其对这一时期温度增暖的变化起了主导作用,而同期AMO贡献近三分之一的北半球温度多年代际变率。

Assessing the influence of natural and anthropogenic forcings on Northern Hemisphere(NH)temperature over the past millennium contributes to a better understanding of the physical mechanisms of climate change for the special periods of the past(e.g.,Medieval Climate Anomaly,MCA,900~1100 A.D.;Little Ice Age,LIA,1450~1850 A.D.;and Current Warm Period,CWP,851~1992 A.D.).This kind of study also provides important reference for the prediction of future climate change.In this paper,we use previously published six tree-ring based millennial-length NH temperature reconstructions to separate the contributions from natural forcing(volcanic,solar,Earth’s orbital parameter),anthropogenic forcing(greenhouse gas concentrations,tropospheric aerosol concentrations,land use change)and internal variability(the multidecadal internal component of North Atlantic and North Pacific SST,referred to simply as AMO and PMO)to the extratropical NH(30°~70°N)summer temperature changes over the period 870~1992 A.D.by approach of Multiple Linear Regression.We found that about 73%of the extratropical NH summer temperature change on time scales longer than 30 years can be explained by these all drivers over the last millennium.The internal climate variability,such as AMO and PMO,may play an important role in the extratropical NH summer temperature during the MCA(900~1100 A.D.),while the volcanic forcing is the dominant factor during the LIA(1450~1850 A.D.).Since 1851 A.D.,anthropogenic forcing contributed nearly 50%of temperature variance,leading to the long-term warming trend,whereas the AMO contributed nearly a third of the temperature multidecadal variability of this period.