Understanding the trends of heat risk

Extreme heat is often described through broken temperature records, but the real story lies in who is exposed, how risk compounds over time, and where systems begin to fail. Visual data helps make these patterns visible. It translates abstract warming trends into concrete signals, showing where heat is intensifying and how it intersects with social and infrastructural vulnerabilities.

These charts do more than illustrate rising temperatures. They reveal trajectories and cascading impacts that are easy to miss in headlines alone. Together, they show why extreme heat is no longer a seasonal anomaly, but a persistent risk shaping systems around the world.

The new normal

This graph tracks how global surface air temperatures have diverged from pre-industrial levels and how rapidly that divergence has accelerated. What appears as modest year-to-year variation in the mid-20th century shifts into a sustained upward trend from the 1980s onward. In recent years, global temperatures consistently exceed +1°C above pre-industrial levels. The sharp rise over the past decade underscores a structural shift: chronic heat is becoming the baseline condition rather than the exception.

Ocean warming leads to cascading climate risk

This map from the Copernicus 2025 Climate report shows how sea surface temperatures have diverged from historical averages across the globe, revealing widespread and uneven ocean warming. Large areas of the Atlantic, Pacific, and Indian Oceans are significantly warmer than average, with some regions reaching record or near-record conditions.

These anomalies matter because oceans play a central role in regulating Earth’s climate system. Warmer seas store and redistribute vast amounts of heat, influencing atmospheric circulation, weather patterns, and the intensity and persistence of extreme heat on land. Elevated sea surface temperatures contribute to hotter nights, longer heatwaves, and compound hazards such as marine heatwaves, coral bleaching, and disrupted fisheries, each with cascading ecological and socioeconomic impacts.

How urbanization is reshaping heat risk

This chart shows the steady increase in the share of people living in cities across regions over recent decades, reshaping how populations experience extreme heat. As urban areas expand, more people are exposed to dense built environments where concrete and asphalt absorb and retain heat, nighttime cooling is reduced, and access to shade is limited. As a result, rising temperatures are often felt more intensely in cities than in surrounding rural areas.

This trend also helps explain growing pressure on urban systems. Higher urban populations increase demand for cooling energy, strain water and transport infrastructure, and intensify health risks during heat events. However, the pace and form of urban growth vary widely across countries, shaping uneven exposure and differing levels of protection.

Heat stress is on the rise globally

This map compares how the number of days with strong heat stress and strong cold stress in 2025 differ from historical averages across the globe. The contrast is significant. Large parts of the world experienced substantially more days of strong heat stress than average, while many regions saw fewer days of strong cold stress.

The increases are especially pronounced across parts of Africa, South Asia, the Middle East, and the Americas, where prolonged exposure can compound risks to health, livelihoods, and infrastructure. At the same time, the reduction in cold stress days reflects a broader shift in seasonal extremes, where warming alters the distribution of risk rather than simply replacing one hazard with another.

Extreme heat is expanding not only in intensity, but also in duration and geographic reach. Longer heat periods reduce opportunities for recovery between events, increase demand for cooling, and extend the window of risk for outdoor work and vulnerable populations. These maps make visible how climate change is increasingly experienced through everyday daily conditions.

 

Source: undrr.org