Ministry of Education Key Laboratory for Earth System Modeling, Department of Earth System Science, Tsinghua University, Beijing, 100084, China.
Joint Center for Global Change Studies, Beijing, 100875, China.
Sci Rep. 2018 Dec 21;8(1):18047. doi: 10.1038/s41598-018-36311-5.
The summer surface air temperature (SAT) in the Humid Subtropical Climate Zone in India, exhibits a significant cooling trend (-3 °C/40 yrs.) in CRU observational data during 1961-2000. Here we investigate the contribution of internal and external factors, which are driving this cooling trend. Using the Community Earth System Model-Large Ensemble (CESM-LE), we analyze the historical climate change in presence of internal climate variability. Most of the model ensemble members could reproduce this amplified cooling (<-3 °C) as shown from CRU data. Further analyses reveals that external forcing displays a strong cooling effect over this region, while internal variability displays mixed cooling (in most cases) and warming signals. The signal to noise ratio i.e. the ratio of external forcings and internal climatic variability is less than 1, which indicates that internal climatic variability dominates over the forced response. Furthermore, to quantify the role of different external forcing factors we used the CCSM4 single forcing simulations. The simulation results from CESM-LE and CCSM4 suggest that the cooling trend over the region is primarily due to the combined influence of internal variability (73%) and partly due to aerosol (~10%) and ozone only forcing, which strongly mask the warming effect of GHG and solar forcing.
在印度湿润亚热带气候区，1961 年至 2000 年期间，CRU 观测数据显示夏季地表气温（SAT）呈现显著降温趋势（约-3°C/40 年）。本研究旨在探究导致这一降温趋势的内部和外部因素的贡献。利用地球系统模式大集合（CESM-LE），我们分析了存在内部气候变率的历史气候变化。从 CRU 数据可以看出，大多数模型集合成员能够再现这种放大的降温（<-3°C）。进一步的分析表明，外部强迫在该地区表现出强烈的冷却效应，而内部变率则显示出混合冷却（在大多数情况下）和变暖信号。即外部强迫和内部气候变率的信号与噪声比小于 1，这表明内部气候变率支配着强迫响应。此外，为了量化不同外部强迫因素的作用，我们使用了 CCSM4 单强迫模拟。CESM-LE 和 CCSM4 的模拟结果表明，该区域的降温趋势主要归因于内部变率（约 73%）和部分归因于气溶胶（约 10%）和臭氧强迫的综合影响，这强烈掩盖了温室气体和太阳辐射强迫的变暖效应。
