20世纪太平洋海温变化中人为因子与自然因子贡献的模拟研究

Contributions of natural and anthropogenic forcings to the twentieth-century Pacific sea surface temperature variability simulated by a climate system model

基于中国科学院大气物理研究所大气科学和地球流体力学国家重点实验室(LASG/IAP)发展的气候系统模式FGOALS_gl对20世纪太平洋海温变化的模拟,讨论了自然因子和人为因子对20世纪太平洋海温变化的相对贡献。观测资料表明,20世纪太平洋平均的SST变化主要分为3个时段:20世纪上半叶的增暖,40—70年代的微弱变冷,70年代之后的迅速增暖。20世纪太平洋SST变化的主导模态是全海盆尺度的振荡上升模态,其次为PDO振荡型,在70年代末PDO存在明显的年代际转型。通过全强迫试验、自然强迫试验、控制试验对上述现象进行归因分析,结果表明,人为因子和内部变率都对第一次增暖有贡献,而人类活动(主要是温室气体的增加)是70年代之后太平洋SST迅速增暖的主要原因。分区域来看,在两个增暖时段中,影响黑潮延伸体区SST变化的主要是自然因子和内部变率,影响其它海域SST变化的则主要是人为因子。全强迫试验可以较好的模拟出前两个模态的空间分布及时间序列。在没有人为因子的影响下,PDO成为太平洋海温变化的主导模态,其年代际转变发生在60年代中期,意味着人为因子是全海盆振荡增暖的主导原因,并且它使得年代际转型滞后了10a。因此,自然因子是导致SST年代际转型中的主导因子,人为因子有"调谐"作用。

Contributions of natural and anthropogenic forcings to the twentieth-century Pacific sea surface tempera-ture （SST） decadal variability are evaluated with a climate system model named FGOALS_gl developed by LASG/IAP .The observational data shows that there are three typical periods of the twentieth-century Pacific SST varia-bility ：a warming tendency in the early twentieth-century ,the weak cooling during 1940s-1970s and the strong warming trend after the 1970s .The first leading mode of the twentieth-century Pacific SST variability features an oscillatorily warming in the whole Pacific basin ,and the second one appears as Pacific Decadal Oscillation （PDO） with a significant inter-decadal transition in the late-1970s .The simulations support that the early stage warming is resulted from a combination of the anthropogenic forcing and the internal variability .And the pronounced late twentieth-century warming is dominated by the increase of greenhouse gases （GHGs） forcing .During the two war-ming periods of the twentieth-century ,the natural forcing and internal variability dominate the changes in Kuroshio Extension （KE） region ,and the anthropogenic forcing dominates the changes in other parts of Pacific .The first two leading modes of the twentieth-century Pacific SST variability can be reproduced by the all-forcing run .The PDO would become the dominant mode and the inter-decadal transition would take place in the mid-1960s if the an-thropogenic forcing is not included .These results indicate that the anthropogenic forcing dominates the warming in the whole Pacific basin and leads to a 10 a delay of the inter-decadal transition .Therefore ,the inter-decadal transi-tion of PDO phase is caused by natural forcing ,while the anthropogenic forcing can modulate the transition point .