在过去一个世纪中，人类活动造成温室气体和气溶胶排放量大幅度升高，这使得两者成为并存于大气中的主要人为强迫因子。一般而言，温室气体（如CO2）和人为气溶胶往往具有近乎相反的热力效应，因此它们各自所引起的气候效应可能会相互抵消，或产生一定程度的非线性效应。我院青年教师邓洁淳博士和徐海明教授，与美国纽约州立大学奥尔巴尼分校Aiguo Dai教授合作，利用海气耦合模式CESM1模拟研究了CO2和人为气溶胶引起的非线性气候效应，相关成果发表在Journal of Climate。

研究发现，尽管CO2和人为气溶胶所引起的全球平均大气层顶辐射通量、近地面气温和降水的非线性响应较小，但在特定季节的北极和其他热带外地区却存在显著的大气非线性响应。由于海冰对CO2和人为气溶胶引起的温度变化具有明显的非对称性响应，当两个强迫因子共同作用时，秋季北极海冰的减少量相比其对单个强迫因子响应的线性叠加要偏少，从而通过减少海洋向大气的能量释放来进一步减缓北极增暖。非线性气候响应还明显存在于东亚夏季的降水变化，即表现为与CO2效应相反的东亚雨带北移。而在冬季，CO2引起的大气环流变化会影响欧洲地区气溶胶的向外输送，导致局地气溶胶含量偏多，并最终通过气溶胶的直接和间接效应引起区域热力响应，形成显著的非线性气候响应（如下图）。该研究成果强调了在对季节性或区域性气候进行归因分析时，需要注意考虑CO2和人为气溶胶产生的非线性气候效应。

Figure 1. Spatial distributions of winter (DJF) mean (a) aerosol optical depth (AOD) changes (shading; ×0.01) in the aerosol-forced run (AER) relative to the control run (CTL), and climatological-mean 925-hPa horizontal winds in AER (vectors; m/s) and (b) AOD changes (shading; ×0.01) and 925-hPa horizontal wind anomalies (vectors; m/s) in the CO2-forced run (GHG) relative to CTL. Only changes statistically significant at the 95% confidence level based on a Student’s t test are plotted in (a) and (b). The red rectangle indicates central northern Europe (50o–70oN, 0o–60oE). (c) Scatterplot of 925-hPa zonal wind change due to the CO2 forcing (x axis; m/s) and nonlinear AOD at 550 nm change (y axis; ×0.01) in DJF averaged over central northern Europe. (d) As in (c), but for 925-hPa zonal wind change due to the CO2 forcing (x axis; m/s) and nonlinear surface air temperature change (y axis; oC). In (c) and (d), each circle indicates a model year, the red line indicates the regression line, and the regression equation and the correlation coefficient are given at the top-right corner.

论文信息：

Deng, J.*, A. Dai, and H. Xu, 2020: Nonlinear climate responses to increasing CO2 and anthropogenic aerosols simulated by CESM1. Journal of Climate, 33, 281–301, https://doi.org/10.1175/JCLI-D-19-0195.1.