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Expected Trends and Surprises for Study on Seasonal Extreme Temperature Events Across North America


Extreme temperatures, hot and cold, can have a dramatic impact on human health in terms of both physical health (e.g., mortality in heat waves) and economic health (e.g., energy demands during a cold spell). While most related studies usually focus on changes in the average, or mean, temperature, extreme weather events are disproportionately understudied compared to their greater impact on human life. In 2017, CPO’s Climate Observations and Monitoring (COM) program funded the “Developing extreme event climate change indicators related to human thermal comfort” project. Findings from that project have recently been published in a study in the International Journal of Climatology. The study examines North American extreme temperature events (warm and cold) and extreme dew point events (humid and dry) by investigating events’ trends across three traits: frequency, duration, and geographic extent. 

Overall, the study reports that extreme warm events are increasing in frequency, duration, and extent while extreme cold events are decreasing. For the US, these changes are most evident in the eastern region. Extreme humid events are increasing in frequency and duration throughout the northeastern US while extreme dry events are decreasing in the same area, with an increase in extreme dry events in the southwest. The summer season (July-September) had the largest amount of changing trends, followed by the autumn and winter seasons. By studying seasonal trends, the researchers uncovered some surprises that seemed contrary to the overall patterns observed. For example, the western US showed little to no significant change in extreme temperature events across the entire year, but when examined seasonally showed a significant increase in cold events occurring in the fall season which were then balanced by a decrease of cold events occurring in the spring and summer seasons. The study also found that an increase in mean temperature does not always mean an increase in extreme warm events. While the Candiain Arctic is rapidly warming and did show a significant decrease in extreme cold events, there was only a moderate increase in extreme heat events. The researchers emphasize that these instances where mean temperature trends do not reveal the whole story are the most crucial findings of their work. 

Read the study »

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