The China Meteorological Administration (CMA) has recently developed a new global monthly land-surface air temperature data set called CMA GLSAT. Using it researchers from the administration reanalysed the change in global annual mean land-surface air temperature during three time periods (1901–2014, 1979–2014 and 1998–2014) to see if there was any evidence of a hiatus or pause in recent surface global warming.
The CMA GLSAT-v1.0 data has its sources in the three original global data sets (CRUTEM4, GHCN-V3 and BEST), eight national data sets (Canada national climate and weather data archive, Australia high-quality climate change data set, United States Historical Climatology Network (USHCN) data set, Korean exchange data set, Vietnam exchange data set, and the data sets of the CMA, Russian Meteorological Agency and Japan Meteorological Agency), and four regional data sets (South American regional data set, Africa regional data set, European regional data set, and Antarctic climate data)
In preparing the new database Xiubao Sun and colleagues from the CMA say they addressed a number of problems with other surface temperature databases, in particular the relatively poor coverage of stations across Antarctica, Africa, South America, and Asia. They note that the IPCC AR5 report concluded that the warming trends in these regions are associated with a lower confidence level. They also improved the absence of early period stations, especially before 1940.
The researchers find very clear evidence for the recent warming hiatus. Their results show linear trends of 0.104 °C per decade, 0.247 °C per decade and 0.098 °C per decade for the three periods, respectively. The trends were statistically significant except for the period 1998–2014, the period that is also known as the ‘‘warming hiatus”.
Table 1: Sun et al. 2017
The annual mean surface temperature anomaly time series for both hemispheres and the globe over the period 1901–2014 are shown in their Fig 1. The linear trends of annual mean surface temperature for SH, NH and the globe were 0.088 °C per decade, 0.115 °C per decade and 0.104 °C per decade, respectively, all statistically significant at the 5% confidence level. Much of the hemispheric and global warming occurred in two distinct periods, from the 1910s to the late 1930s and from the early 1980s to the mid-2000s. The relatively cool periods or stable periods appeared in the 1900s, 1940s–1970s and between 2005 and 2014. (Click on image to enlarge.)
Overall, they find that the annual warming was larger in the NH (0.115 °C per decade) than in the SH (0.088 °C per decade). From the early 1950 to early 1970s, however, the SH exhibited an insignificant warming, whereas the NH exhibited a slight cooling. The land warming from the early 1980s was much more remarkable in the NH than in the SH. They add it is also clear that the global mean surface temperature change was largely determined by the NH because there were a much greater number of grid boxes containing data in the NH than in the SH.
The researchers conclude that from 1979 to 2014, the mean surface temperature anomalies in the SH, the NH and the globe showed annual unprecedented and highly significant warming trends, reaching 0.138 °C per decade, 0.317 °C per decade and 0.247 °C per decade, respectively. From 1998 to 2014, however, he two hemispheres and the globe experienced the ‘‘warming hiatus”, with the SH, NH and global lands registering insignificant warming trends of 0.087 °C per decade, 0.105 °C per decade and 0.098 °C per decade, respectively.
During the recent ‘‘warming hiatus” they note that a high incoherence in global surface temperature changes can be seen, with the abnormal warming in Arctic areas neighboring the Eurasian Continent and North Atlantic Ocean and remarkable cooling in North America, East and Central Asia, northern Australia and southern Africa. The slowdown of climate warming, they say, seems to mainly occur at the low and middle latitudes of the hemispheres, and especially in the boreal cold season.