2021 Texas Cold Snap: Manifestation of Natural Variability and a Recent Warming Trend / Dr Pei-Chun Hsu (Research Center for Environmental Changes, Academia Sinica)

Abstract: The February 2021 North American cold snap caused the worst energy infrastructure failure in Texas state history, leaving millions without electricity or heating amid freezing temperatures. Here we showed that the Texas cold snap occurred in a large-scale background circulation over the North Pacific and North America that was the manifestation of both natural variability and the warming trend since the late 1990s. The anomalous circulation favoring the occurrence of cold events like the one in Texas exhibited the characteristics of the negative Pacific-North American (PNA) pattern and has been enhanced by the observed trend. Numerical experiments showed that the negative PNA pattern could be driven by the La Niña-like sea surface temperature (SST) anomalies in the equatorial eastern Pacific in the interannual-decadal time scale and the SST warming trend in the subtropical North Atlantic in longer time scale. Our study demonstrated the importance of extratropical wave activity and intrinsic mode in causing the extreme coldness in North America.