When is a Heat Wave Just a Heat Wave, and When is it Climate Change?

When extreme weather events occur, can we tell if they’re directly attributable to climate change? A new study used the 2023 heat wave in Texas and Louisiana as a test case for establishing processes that tease out whether particular weather events are climate related.

“Our main goal with this project is to be able to tell communities that are affected by extreme weather events whether they will continue to see more events like this in the future,” says Carl Schreck, senior research scientist with North Carolina State University’s North Carolina Institute for Climate Studies (NCICS). “Getting this information to them in a timely manner will help them make informed decisions about hardening infrastructure or rebuilding after a weather event.”

Schreck and a team of scientists from NC State, the National Oceanic and Atmospheric Administration (NOAA), the University of Colorado, Boulder and Princeton University set out to establish a routine process for evaluating extreme weather events.

The test case for the study was an extreme heat wave that occurred in Texas and Louisiana in 2023. The event was notable for its duration – it lasted almost the entire summer. Most heat wave measurement metrics are designed for events that last three to seven days.

“The other interesting piece of this event is that it occurred within the daytime warming hole,” Schreck says. “The warming hole refers to an area in the central U.S. where temperatures have not warmed at the same rate that we see over most other places. This is because increased precipitation there has kept afternoon temperatures from warming.”

The scientists used a two-step process to determine whether the heat wave was an anomaly or part of a new pattern. First, they took historical data from heat monitoring stations across the U.S. from the past 100 years to see how unusual 2023 was. Then they compared that data with the frequency of heat waves in both past and present predictive computer models.

Comparing those predictive models can indicate whether climate change is playing a role in the event.

“A similar drought wouldn’t have been as hot 50 years ago,” Schreck says. “That tells us the heat wave is directly related to climate change and that we will see even hotter heat waves in the future.”

Now that these methods have been established, the researchers plan to use them to determine the role of climate change in future heat waves.

The work appears in Environmental Research: Climate and was supported by NOAA’s Climate Program Office and the U.S. Department of Commerce. David Coates and John Uehling, research associates at NCICS, and NC State research professors Xiangdong Zhang and Kenneth Kunkel are co-authors. David R. Easterling and Russell S. Vose, NOAA/National Centers for Environmental Information; Joseph J. Barsugli, University of Colorado Boulder; Andrew Hoell, NOAA/Physical Science Laboratory; Nathaniel C. Johnson, NOAA/Geophysical Fluid Dynamics Laboratory; and Zachary M. Labe, Princeton University, are also co-authors.

-peake-

Note to editors: An abstract follows.

“A Rapid Response Process for Evaluating Causes of Extreme Temperature Events in the United States: The 2023 Texas/Louisiana Heatwave as a Prototype”

DOI: 10.1088/2752-5295/ad8028

Published: Oct. 9, 2024 in Environmental Research: Climate
Authors: Carl J. Schreck III, David A. Coates, Kenneth E. Kunkel, John Uehling, Xiangdong Zhang, North Carolina State University, Cooperative Institute for Satellite Earth System Studies; David R. Easterling, Russell S. Vose, NOAA/National Centers for Environmental Information; Joseph J. Barsugli, Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder; Andrew Hoell, NOAA/Physical Science Laboratory; Nathaniel C. Johnson, NOAA/Geophysical Fluid Dynamics Laboratory; Zachary M. Labe, Princeton University

Abstract:
As climate attribution studies have become more common, routine processes are now being established for attribution analysis following extreme events. This study describes the prototype process being developed through a collaboration across NOAA, including monitoring tools as well as observational and model-based analysis of causal factors. The prolonged period of extreme heat in summer 2023 over Texas, Louisiana and adjacent areas provided a proving ground for this emerging capability. This event posed unique challenges to the initial process. The extreme heat lasted for most of the summer while most heat wave metrics have been designed for 3–7 day events. The eastern portion of the affected area also occurred within the so-called summer-time daytime warming hole where the warming trend in maximum temperatures has been mitigated wholly or in part by increased precipitation. The extreme temperature coincided with a strong—but not record—precipitation deficit over the region. Both observations and climate model simulations illustrate that the temperatures for a given precipitation deficit have warmed in recent decades. In other words, meteorological droughts today are hotter than their historical analogs providing a stronger attribution to anthropogenic forcing than for temperature alone. These findings were summarized in a prototype plain language report that was distributed to key stakeholders. Based on their feedback, the monitoring and assessment tools will continue to be refined, and the project is exploring other climate model large ensembles to increase the robustness of attribution for future events.

This post was originally published in NC State News.