The Science

An extreme heat event occurred near the North Pole in late December 2015. The near-surface air temperature was above 0 °C, exceeding the melting point for pure water ice. Although this event has been extensively studied, knowledge about similar events remains very limited. In this study, researchers used a dataset that integrates observational data with advanced numerical simulations to investigate the characteristics, drivers, and trends of such events over the past four decades. Findings reveal that High Arctic heat extremes were typically short-lived, lasting less than half a day in most cases. Strong moisture intrusions in the atmosphere, also known as atmospheric rivers (ARs), were the primary catalyst for these events. As the Earth continues warming, these ARs and heat extremes are expected to occur with greater frequency, intensity, and duration.

The Impact

The Arctic has warmed up about four times faster than the rest of the world, leading to more frequent short-lived wintertime heatwaves with temperatures rising above the melting point. Heat extremes with a near-surface air temperature above 0 °C are expected to have a melting effect on the underlying snow and sea ice. Understanding what causes these warm spells helps scientists better predict how much sea ice in the Arctic can remain each winter. This is important because winter sea ice coverage directly influences how much sea ice remains for summer melting. Better predictions can help protect Arctic wildlife and support communities by preparing for abrupt changes in the environment.

Summary

The Arctic has experienced rapid warming in recent decades, particularly during winter months, leading to an increased frequency of extreme warming events when temperatures rise above the melting point of 0 °C. These events significantly affect the underlying sea ice. Understanding these events is crucial for predicting sea ice and climate conditions in the Arctic more accurately.

In this study, scientists characterized winter heat extremes over the High Arctic (poleward of 80°N), defined as near-surface air temperature going above 0 °C. They found that these events not only occurred rarely, but also lived shortly—often lasting less than a day. By examining the associated weather patterns, the researchers discovered that certain environmental conditions, which steer storms and warm/moist air toward the pole, favor the occurrence of these events. They also learned that ARs—long streams of moist air in the atmosphere—were usually involved, especially for places closer to the North Pole.

Over the past 40 years, these brief warming events have become more common and lasted longer. This has very important implications because such heat extremes can initiate and speed up ice melting and affect Arctic ecosystems and water cycles. As the planet continues to warm up, these warm spikes in temperature are expected to happen more often, which could have significant impacts on the Arctic and even the entire globe.

PNNL Contact

Hailong Wang, Pacific Northwest National Laboratory, hailong.wang@pnnl.gov

Funding

This research has been supported by the Department of Energy, Office of Science, Regional and Global Model Analysis program area, as part of the HiLAT-RASM project.