Tracking the Teletherms: The spatiotemporal dynamics of the hottest and coldest days of the year

TL;DR

This study analyzes the timing of the hottest and coldest days of the year across the US over 160 years, revealing regional variations, shifts due to climate change, and evaluating climate models' accuracy.

Contribution

It introduces the concept of Teletherms as a new, robust measure of local climate change and provides a comprehensive analysis of their spatiotemporal dynamics.

Findings

Large regional variation in Teletherm dates

Significant shifts in Teletherm timing over time

Climate models show considerable error in predicting Teletherms

Abstract

Instabilities and long term shifts in seasons, whether induced by natural drivers or human activities, pose great disruptive threats to ecological, agricultural, and social systems. Here, we propose, measure, and explore two fundamental markers of location-sensitive seasonal variations: the Summer and Winter Teletherms---the on-average annual dates of the hottest and coldest days of the year. We analyse daily temperature extremes recorded at 1218 stations across the contiguous United States from 1853--2012, and observe large regional variation with the Summer Teletherm falling up to 90 days after the Summer Solstice, and 50 days for the Winter Teletherm after the Winter Solstice. We show that Teletherm temporal dynamics are substantive with clear and in some cases dramatic shifts reflective of system bifurcations. We also compare recorded daily temperature extremes with output from two regional climate models finding considerable though relatively unbiased error. Our work demonstrates that Teletherms are an intuitive, powerful, and statistically sound measure of local climate change, and that they pose detailed, stringent challenges for future theoretical and computational models.