Emergence of a climate signal in US heat waves

The number and severity of heat waves have increased in recent decades and is projected to continue increasing into the 21^st century. Population growth coupled to the fact that extreme heat is the leading weather-related cause of death in the US calls for the need to identify the relative roles of natural variability and human-caused climate change on these extremes. Therefore, knowledge on the Time of Emergence (ToE), or the years that the human contributions to climate change will become more important than natural variability in causing heat waves, is crucial for better mitigation and adaptation efforts.

In a recent paper appearing in Nature Climate Change, the authors identified the most common heat wave patterns over the US by clustering extreme events by their spatial distribution. The study shows that there are four regions of the US where human-caused climate change will ultimately overtake natural variability as the main driver of heat waves in the coming decades. Climate change will drive more frequent and extreme summer heat waves in the western US by late the 2020s, the Great Lakes region by the mid-2030s, and in the northern and southern Plains by the 2050s and 2070s, respectively. The later onset of climate change-fueled heat waves across the Great Plains is found to be a result of the projected increase of the Great Plain low-level jet and moisture transport, attenuating the surface warming associated with climate change. In contrast, a projected reduction in storminess over the western US and Great Lakes regions will increase the possibility of heat waves there, exacerbating the mean temperature increase due to climate change, thus producing earlier ToE.

This study is part of a larger effort to better predict heat waves. Understanding the driving forces behind heat waves is crucial for informing public health security and extreme heat mitigation strategies. Research has tended to focus on predicting extremes, such as tornadoes or hurricanes, when heat waves are actually causing many more weather-related deaths in the US. This study helps fill that gap to develop effective heat wave prediction, which helps communities be better prepared.