Under global warming, regionally extreme cold events occur occasionally and cause hazards and damages. The Tibetan Plateau, with its high elevation and the unique ecosystem, is one of the most vulnerable regions responding to climate change. In early spring 2019, a cold surge hit the southeastern Tibetan Plateau.

Researchers led by Prof. DUAN Jianping from the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences and their collaborators from Chinese Academy of Meteorological Sciences and Met Office, UK conducted event attribution study for the extreme early-spring cold surge occurred in the southeastern Tibetan Plateau in 2019.

The study was published in Bulletin of the American Meteorological Society.

"We want to understand such cold events against the background of climate warming in this particular region. Would it happen more often or less often? In particular, what's the role of the influence of human activities?" said Prof. DUAN.

Snowed covered Biru County, Southeastern Tibetan Plateau. (Image by DUAN Jianping) 

The results showed that the core region of the cold event located in 28-35°N, 90-100.3°E, where the average daily maximum air temperature (Tmax) during February 25 to March 11 of 2019 is record-breaking since 1966. It was 2.55℃ lower compared to the 1981-2010 climatology.

The return period of the 2019 cold event is about once in 34 years, but the model simulations suggest that it could be once every few years if there is no influence of human activities. Without human activities, i.e., anthropogenic forcing, the regional average maximum air temperature of early spring 2019 in the study area would be 1.9℃ lower than the actual.

A formal event attribution analysis based on HadGEM3 developed at Met Office and CMIP6 ensemble simulations indicated that anthropogenic forcing has reduced the likelihood of extreme early-spring cold event over the southeastern Tibetan Plateau similar to 2019 by about 80%.

"So in this particular region, anthropogenic forcing actually reduces the frequency of such extreme cold events," said Prof. DUAN. "The next step will be to see how the decreased frequency of cold extremes in the special region affects the phenology and ecosystem."

This research was supported by the National Natural Science Foundation of China, the National Key R&D Program of China, and U.K.-China Research and Innovation Partnership Fund.