A meteorological observation center in Hong Kong. Photo: Courtesy of Li Qingxiang

An international team lead by Chinese scientists using a newly merged temperature dataset which is able to cover almost the entire surface of the globe found that there has been a consistent trend of increased global warming since the 1850s, indicating that the previous datasets underestimated global temperature anomalies between 1998 and 2012.  

The newly merged global surface temperature dataset, including reconstructed land and marine measurements from the 1850s to 2018, was a global monthly surface temperature dataset spanning 1854 to 2018. It gave improved coverage of the Earth's surface, with up to 99 percent of the globe between 1850 and 1950 and 90 percent of the globe from the 1950s onwards. The previous dataset could only cover around 80 percent of the globe, Li Qingxiang, a professor at the School of Atmospheric Sciences and Key Laboratory of Tropical Atmosphere-Ocean System from Sun Yat-Sen University, told the Global Times on Thursday.

The land section of the dataset was developed by Chinese scientists, while the marine section came from the National Oceanic and Atmospheric Administration's National Centre for Environmental Information in the US.

The results showed that the global surface temperature has increased by 0.137 degrees per decade since 1950, while the previous dataset showed the global temperature increased by only 0.128 degrees per decade since 1950, Li said.

The research and results, led by Li, was published on Thursday in the scientific journal Advances in Atmospheric Sciences. 

Earth is warming rapidly, but there is too little observational data in some regions such as the Arctic or high-altitude areas like the Qinghai-Tibetan plateau to adequately and consistently assess temperature variations across the globe, Li said, noting that the global surface temperature is one of the most important and accurate essential climate variables in the Earth system.

This inadequacy has prevented scientists from comprehensively assessing global temperature changes since the industrial revolution.

The importance of a complete global coverage dataset was emphasized in recent studies of the "hiatus" period, when global warming appeared to slow from 1998 to 2012, especially for observations of high-latitude regions such as the Arctic, Li said.

Many scientists believe that the lack of coverage of global temperature datasets led to the underestimation of global warming trends between 1998 and 2012, Li said. However, the recent unreconstructed dataset has already done away with the idea of a "warming hiatus".

Due to the enormous uncertainties surrounding the ice surface temperature change of the Arctic, the current study excluded this aspect of the changes, given that the total permanent ice covered area is very limited (about 0.65 percent of the globe), Li said.