Understanding the Impacts of Climate Change on Record Heat in 2023

October 10, 2023 / 7 min read

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The interplay between a maturing El Niño and climate change holds the potential to shape weather patterns, influencing heat distribution and contributing to unprecedented conditions.

I recently spoke with the Verisk Climate Advisory Council about the remarkable temperature records that shaped this summer, not only within the United States but worldwide. Our conversation revolved around the intersecting influences of climate change and El Niño and how they might collectively contribute to extreme weather. We also explored the potential scenarios for the remainder of the year regarding hurricane and wildfire activity. In this Visualize article, I’ll condense the essence of our dialogue, incorporating insightful comments from the Council members to help insurers better prepare for the upcoming hurricane and wildfire season.

While every summer typically witnesses sporadic heatwaves in various places worldwide with momentary spikes in temperatures that slightly surpass existing records, 2023 has stood out by aligning all three distinct characteristics. Noteworthy examples include the scorching 31-day streak of temperatures exceeding 110°F (43°C) endured by Phoenix, AZ, which significantly eclipsed the previous record of 18 consecutive days set in 1974.

Dr. Ken Kunkel—professor at North Carolina State University, lead scientist for the US National Climate Assessment Reports, expert in temperature and precipitation climatology and extremes, and a Verisk Climate Advisory Council member—commented in depth on the significance of many recent temperature records. He noted in particular that the streak of 16 days with nighttime temperatures not dropping below 90°F (32°C) in Phoenix might be an all-time US record (excluding Death Valley’s temperature extremes), surpassing not only the region’s previous record of 7 days in Phoenix but also the previous US record of 11 days in Needles, CA.

He also talked about what happened in El Paso, TX, where the maximum temperature held at 100°F (38°C) or higher for a staggering 42 consecutive days. This streak marks a considerable increase from the prior record of 23 consecutive days, documented in 1994. Around the same period, northwest China documented an unprecedented high temperature surpassing 122°F (50°C), while the Persian Gulf encountered a heat index exceeding 150°F (65.5°C) with a dewpoint of 90°F (32°C). That dewpoint translates to a wet bulb temperature of 93°F (34°C), edging close to the human threshold of 95°F (35°C), beyond which effective cooling through sweating becomes challenging.

Given the prevalence of record-breaking heatwaves in diverse regions, it’s unsurprising that the Earth achieved its highest temperature recorded on July 3rd. Astonishingly, this feat was replicated on July 4th, 5th, and even on July 6th. Figure 1 below illustrates that nearly every day in 2023 has witnessed global temperatures at or above the 90th percentile, based on data extending back to 1940.

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Figure 1: Daily global temperatures for all years 1940-2023 (and counting). Note that earlier years were generally cooler years and recent years are mainly hot years. Check the data here.

The prolonged record-breaking heat worldwide may foreshadow a recurring global scale pattern. To produce simultaneous extreme heat across much of the northern hemisphere, high-pressure ridges must stagnate over the continents, corresponding to a wave-7 configuration in the jet stream.

Dr. Cindy Bruyère, CPAESS Deputy Director at the University Corporation for Atmospheric Research (UCAR) and a member of the Verisk Climate Advisory Council, pointed out that simulations from the latest global climate models support the potential for a future increase in the occurrence of wave-7 configurations that could impact several continents simultaneously.

Wave-7 configurations would become more frequent due to the ongoing polar amplification, which is diminishing the temperature contrast between the poles and the equator. Consequently, this alteration is influencing the formation of different wave patterns. A similar pattern was in place and persisted for days during a global heat wave in 2021, as shown in Figure 2.

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Figure 2. Example of wave-5 (left) and wave-7 (right) patterns from the 2021 heat wave. Prof. Stefan Rahmstorf on Twitter: “The historic heat wave in the western US coincides with resonance conditions and high-amplitude stationary waves in the atmosphere. Source here.

But climate change wasn’t the only mechanism at play this summer; a maturing El Niño allowed more heat over larger areas of the globe. Historically, El Niño years are the hottest, and there were early signs that this El Niño would be moderate to strong. The NINO3.4 index has increased by more than 1.5°C since January, putting it in the top ten percent of developing El Niño events that have transitioned that abruptly. El Niño effects or teleconnections across the globe tend to reach a peak in winter, so time will tell how other characteristics like heavy rains across the southern US pan out.

Intriguingly, despite the eastern Pacific’s escalating temperature and the intensifying El Niño, NOAA and other hurricane forecasting agencies revised their projections for Atlantic hurricane activity upwards, pointing towards an above-average hurricane season. Their prediction contrasts with the conventional expectations tied to El Niño conditions.

This unexpected twist may find its roots in the water temperatures of the Main Development Region (MDR) and the waters along Florida’s coast. Extending across the vast Atlantic, sea surface temperatures (SSTs) currently range 1–2°C above the norm, with even more pronounced warmth enveloping Florida’s vicinity. In particular, the water temperatures exceeding 31°C around Florida serve as a catalyst for a staggering maximum potential hurricane intensity of 190 mph (Category 5) on the Gulf side of the state.

Adding to the discourse, Dr. Bruyère raised concerns regarding the elevated SSTs and their potential to support rapid intensification (such as an increase of at least 30 knots in maximum windspeed in 24 hours) of storms just before landfall, leaving minimal time for adequate evacuation warnings. This vulnerability especially pertains to formidable storms, underscoring the urgent need for heightened preparedness and response measures.

Only small sections of the northwestern Atlantic exhibit temperatures either at or slightly below the normal range. This occurrence could potentially stem from ongoing wildfires in eastern Canada obstructing a portion of sunlight from reaching the ocean’s surface. This heightened wildfire activity appears to influence the broader atmospheric flow patterns, contributing to the sustained presence of a pressure trough. This pressure trough, in turn, fosters cool and somewhat rainy conditions across eastern North America. Concurrently, this pattern may also contribute to the pressure ridge over western North America, accentuating the heat and aridity.

Until now, the wildfire season in the western US has maintained relative calm. However, this tranquility could undergo a rapid transformation in the upcoming autumn if a Santa Ana event emerges in southern California, as Dr. Park Williams, a member of the Verisk Advisory Council, distinguished hydroclimatologist, and professor at UCLA, noted during our discussion, although the heavy rains from Tropical Storm Hilary may have further tempered the near-term risk.

Dr. Williams also noted a heightened concern for the coming year. The extensive heavy rains brought about by numerous atmospheric river events earlier in 2023 are anticipated to lay the groundwork for prime fuel conditions in the subsequent year. This concern particularly escalates in the context of a potential shift toward La Niña conditions next spring.

Despite a decrease in wildfires, the scale of burnt area and the frequency of substantial fires (exceeding 100-200 hectares) have risen. This increase can be partly attributed to the greater fuel availability and the diminished favorability of nighttime firefighting conditions. Higher overnight temperatures, a key hallmark of climate change, result in elevated vapor pressure deficits. Satellite imagery from MODIS indicates a notable shift in nighttime fire behavior. Over the last few decades, fires have exhibited heightened intensity during nighttime while showing relatively consistent patterns during daylight hours, intensifying the difficulties of battling wildfires.

Going into the last quarter of 2023, it seems increasingly probable that this year will etch its mark in history as the hottest globally, driven by the combined forces of climate change and El Niño. Nevertheless, the implications extend beyond mere temperature records. It remains crucial that the convergence of these factors must not pave the way for a heightened likelihood of extreme events, potentially presenting even greater challenges to human well-being and property.

As we navigate the landscape of 2023 and beyond, the insurance industry stands at a critical juncture. The escalating intensity and frequency of extreme events such as hurricanes and wildfires demand a proactive and prepared stance. The ability to respond swiftly and effectively to these challenges not only safeguards the well-being of individuals and communities but also underscores the industry’s commitment to mitigating risks and offering vital protection. By staying primed and responsive, the insurance sector can play a pivotal role in bolstering resilience and aiding recovery during these trying times.