The warmest year 2015 in the instrumental record and its comparison with year 1998

The global annual averaged Surface Air Temperature Anomaly （SATA） in 2015 and its rank in the historical instrumental records are analyzed using the CRU, NASA, and NOAA datasets. All datasets indicate that 2015 is the warmest year, which is 0.74℃ warmer than normal years from 1961 to 1990 in the HadCRUT4 data-set. The most evident warm anomaly occurs over land, especially at high latitudes. The averaged SATA over land is 1.13 ℃, which is 0.54℃warmer than that over oceans （0.59℃）. Because an El Niffo event occurred in 2015 and 1998 and 1998 is also the warmest year in the twentieth century, these two years are compared to explain the formation of the warmest climate. A statistical approach that is known as the Ensemble Empirical Mode Decomposition （EEMD） is employed to isolate the components with different timescales, which range from interannual to centennial and a long-term trend. In 2015 the developing El Niffo may have contributed an anomaly of 0. 1 0℃, while this value is 0.1 8 ℃ for 1998. The contribution of the decadal-multidecadal variability and beyond to 2015 is 0.64℃, which is significantly larger than that of the interannual anomaly components （0.10 ℃）. This indicates that the warmest climate in 2015 occurred in the context of the tirnescales beyond the interannual.

本文利用CRU、NASA和NOAA的近地面气温异常(SATA)数据,对比分析了2015年和1998年的温度异常分布特征,证实了2015年是有观测记录以来温度最暖的一年,并进一步利用EEMD方法探讨了不同时间尺度对2015年温度异常的贡献以及其温度最暖的形成原因。结果表明,年代际及其以上的时间尺度和长期增暖趋势对2015年年平均SATA贡献为0.64°C,远远大于与ENSO信号相关的年际时间尺度的贡献(为0.1°C),说明长时间尺度和全球长期变暖趋势对2015年温度异常的形成有重要贡献。