Last summer, when heat waves swept across large parts of the planet, in many places the oppressive temperatures lingered for days or weeks at a time. A study published on Friday revealed that as climate change warms the planet, heat waves are moving more slowly and lasting longer.
Between 1979 and 2020, the study found that the speed at which heat waves travel has slowed by about 5 miles per day each decade. Additionally, heat waves now last about four days longer on average.
“This has significant impacts on public health,” said Wei Zhang, a climate scientist at Utah State University and one of the study’s authors.
The prolonged presence of heat waves exposes people to life-threatening temperatures for longer periods. It also affects economic productivity, dries out soil and vegetation, damages crops, and increases the risk of wildfires.
Dr. Zhang noted that changes in heat wave behavior have become more noticeable since the late 1990s. While human-caused climate change plays a significant role, natural climate variability also contributes to these changes.
The study is one of the first to track how heat waves move through both space and time.
Rachel White, an atmospheric scientist at the University of British Columbia, expressed her anticipation for research like this, stating that it helps to better understand the mechanisms behind the intensification and frequency of heat waves.
The researchers analyzed temperatures globally from 1979 to 2020 and defined heat waves as contiguous areas covering at least 1 million square kilometers with temperatures at least at the 95th percentile of historical maximums, lasting for at least three days.
Overall, the study found that heat waves are slowing down by about 8 kilometers per day each decade and lasting longer, persisting for an average of 12 days from 2016-20 compared to eight days from 1979-1983.
The researchers also discovered that heat waves are becoming more frequent, averaging 98 per year between 2016 and 2020 compared to 75 per year between 1979 and 1983.
Regional differences were observed, with heat waves lasting longer in Eurasia and North America and traveling farther in South America.
The study used models to simulate temperatures with and without human-induced greenhouse gas emissions, confirming that climate change is a significant driver behind the observed trends in heat wave behavior.
Scientists have noted a weakening trend in air circulation and upper atmosphere winds like the jet streams, particularly in the Northern Hemisphere during the summer. This weakening could contribute to the stalling and prolonged duration of extreme weather events.
While the exact causes of the heat wave slowdown require further research, the negative impacts remain unchanged.
Dr. Zhang emphasized the importance of local efforts to adapt to the changing climate, such as planting more trees and grasses in urban areas and creating cooling centers for vulnerable populations.
While global action to reduce greenhouse gas emissions is crucial, local adaptation strategies are essential to protect communities from the escalating risks associated with heat waves.
