Attribution of extreme weather events: Can individual heat waves be directly linked to climate change?

A collaborative study between several universities and NOAA examined a persistent 2023 heat wave in the southern United States. With the help of climate models accounting for climate change, they determined that these sorts of heat waves will likely increase in the future.

Droughts
Extreme weather events, like heat waves and droughts, are increasing due to climate change. Scientists are implementing data-driven analyses to directly link individual events to climate change.

Devastating hurricanes, severe flooding events, damaging tornado outbreaks, and persistent heat waves have always plagued the United States. Scientists have been trying to definitively determine if the recent increase in extreme events is due to climate change.

North Carolina State University’s Institute for Climate Studies (NCICS) recently conducted a study that examined the 2023 heat wave in Texas and Louisiana. NCICS teamed up with University of Colorado Boulder, Princeton University, and NOAA. The goal was to design a process for determining if individual weather events, like this heat wave, could be the result of climate change.

The heat wave

The event occurred in the summer of 2023 in southern Texas and Louisiana, and was chosen intentionally. Many daily and seasonal temperature records were shattered in cities like El Paso and San Antonio. The heatwave lasted nearly the entire summer, and most indices for measuring heat waves only accommodate for a scale of 3-7 days. This region is also on the cusp of the daytime warming hole.

July Temperatures
Most of Texas and Louisiana experienced an extremely warm July 2023, with temperatures averaging close to 10F above normal in some locations. Source: NOAA Climate.gov

The daytime warming hole is a large portion of the central U.S., from the upper Midwest to the Gulf Coast, that has seen a slower increase in summer average temperatures. This is largely attributed to increased precipitation during the summertime in these areas. The summer 2023 heat wave was accompanied by significantly below-average precipitation.

The process

The overarching question with such an event is whether or not it is anomalous, or if it can be attributed to a larger pattern. Scientists in this study employed a two-step process to try and answer that question for this event. Their goal was also to work towards a systematic process that could be called upon in real-time for future events.

First, they examined 100-year historical data from the robust network of U.S. climate monitoring stations. Using this data, they determined how unusual the 2023 heat wave was in comparison to past heat waves in similar locations. Next, they compared the results of prognostic computer models with the frequency of past heat waves.

The results

Analyses revealed that a drought of similar severity would not have been as hot 50 years ago, on the order of 2-3ºF. The comparison with historical data determined that the likelihood of these sorts of events has increased. Additionally, it appears nighttime temperatures are more anomalously warm during extreme heat events than daytime temperatures.

Climate models have predicted this more pronounced warming to coincide with periods of precipitation deficit. This is directly due to anthropogenic drivers. These same models predict that the exacerbation of global warming will result in an increased number of heat waves of this magnitude.

Participating researchers have published this study with the hopes of refining this attribution process for future use. This will be essential as we prepare for the downstream effects of climate change for decades to come.