In 2026, heatwaves are no longer just “unusually hot days”—they have become longer, more intense, and more frequent.1 According to data from the WMO and the IPCC, the chances of extreme heat events have increased significantly, with some 2024–2025 heatwaves being made up to 35 times more likely due to human-induced climate change.2+1
The science behind this trend involves a combination of a “warmer baseline,” atmospheric stalling, and local urban factors.
1. The “Higher Baseline” Effect3
The most fundamental reason for more heatwaves is that the global average temperature has risen by approximately 1.2°C since the industrial revolution.
- Shifting the Curve: Imagine a bell curve of temperatures. As the average (the middle of the curve) shifts to the right, what used to be an “extreme” hot day becomes a “common” hot day, and previously impossible temperatures become the new extremes.
- Compound Events: Warmer winters and springs mean the ground dries out earlier. When a heatwave hits, the sun’s energy goes entirely into heating the air rather than evaporating moisture from the soil, creating a “feedback loop” that spikes temperatures even higher.
2. Atmospheric Stalling: The “Heat Dome”4
A heatwave becomes dangerous when it stays in one place for weeks. In 2026, scientists are closely monitoring the Jet Stream—the high-altitude river of wind that moves weather systems across the globe.
- Wavy Jet Stream: As the Arctic warms faster than the rest of the planet (Arctic Amplification), the temperature difference that drives the jet stream weakens.5 This causes the wind to become “wavy” and sluggish.
- The “Lid on the Pot”: These slow-moving waves can trap a high-pressure system over a region, creating a Heat Dome.6 This high pressure pushes warm air down, compressing and heating it further, while simultaneously blocking cool air or clouds from entering the area.7+1
3. The Urban Heat Island (UHI) Effect
For the 55% of the global population living in cities, heatwaves are intensified by the built environment.8
- Heat Absorption: Concrete, asphalt, and dark roofs absorb vast amounts of solar radiation during the day and release it slowly at night.9
- The Nighttime “Safety Gap”: The most dangerous part of a 2026 heatwave is often the lack of nighttime cooling. In cities, nighttime temperatures can remain 5°C to 10°C higher than in surrounding rural areas, preventing the human body from recovering from daytime heat stress.
4. Heatwave Trends: Then vs. Now
| Metric | Pre-1950s Average | 2026 Observations |
| Frequency | Rare (Once a decade) | Frequent (Multiple times per summer) |
| Duration | 2–3 days | 7–14+ days |
| Intensity | Peak temps near 38°C (100°F) | Peak temps frequently exceeding 45°C+ (113°F+) |
| Nighttime Relief | Consistent cooling below 20°C | “Tropical Nights” (Lows staying above 25°C) |
The Future: “Climate Departure”
+1
In 2026, experts are warning of Climate Departure—the point at which a “normal” summer in the future will be hotter than the most extreme heatwaves of the past. To combat this, cities are rapidly adopting “Cooling Urbanism,” such as planting millions of trees to increase shade and using reflective “cool pavements” to bounce sunlight back into space.10
