Record-breaking heat has become a defining feature of summers around the world. Recently, scorching temperatures have swept across Europe, North America and Asia, disrupting daily life, straining power grids and increasing health risks. Scientists warn that extreme heat is no longer an isolated weather event but one of the clearest signs of a warming climate. 

According to the World Health Organization (WHO), an estimated 489,000 heat-related deaths occurred globally each year between 2000 and 2019, making extreme heat one of the deadliest weather-related hazards. Older adults, young children, outdoor workers and people with chronic illnesses are particularly vulnerable.

Beyond public health, prolonged heat waves are affecting agriculture, water supplies, energy systems and ecosystems. The Food and Agriculture Organization has warned that climate extremes, including heat and drought, are posing growing threats to global food security by reducing crop yields and increasing production risks. As extreme heat becomes more frequent, improving society's ability to adapt has become an urgent global challenge.

Why is the world getting hotter?

Scientists agree that human-induced climate change is driving more frequent and intense heat waves. Greenhouse gases released from burning fossil fuels have raised Earth's average surface temperature by around 1.3 degrees Celsius above the pre-industrial level, according to the World Meteorological Organization. Even this seemingly modest increase has shifted the climate baseline, making record-breaking temperatures much more likely than they were decades ago.

Climate change alone, however, does not explain every heat wave. Meteorological factors often determine when and where extreme heat occurs. A heat dome – a persistent high-pressure system that traps hot air near the ground – can allow temperatures to build for days or even weeks. Large-scale atmospheric circulation anomalies, a weakened jet stream and natural climate patterns such as El Nino, which temporarily warms parts of the Pacific Ocean, can further intensify heat in some regions. In cities, the urban heat island effect makes matters worse as buildings and paved surfaces absorb and retain heat while limited vegetation reduces natural cooling.

Heat is reshaping everyday life

Extreme heat is placing growing pressure on modern society. High temperatures increase the risk of heatstroke, cardiovascular disease and respiratory illness while reducing labor productivity and driving up electricity demand for cooling. Agriculture is also under strain, as heat stress and prolonged drought reduce crop yields and livestock productivity, threatening food supplies in many regions.

Cities are particularly vulnerable. Dense development, concrete surfaces and limited green space often make urban temperatures several degrees higher than surrounding rural areas. Outdoor workers, including construction workers, delivery personnel and sanitation workers, are particularly vulnerable to prolonged heat exposure, highlighting the need for stronger occupational protection.

Science and nature offer solutions

Around the world, governments are adopting both technological and nature-based solutions to reduce heat risks. More accurate weather forecasting and heat-health early warning systems help authorities issue timely alerts, while expanding urban forests, parks, wetlands and reflective building materials can lower city temperatures and improve resilience. WHO has called on countries to integrate heat-health action plans into urban planning and emergency response systems.

For example, Chongqing, one of China's best-known "furnace cities," has introduced a river-water cooling system that uses water from the Jialing River to provide energy-efficient cooling. Tang Shijie, an engineer with Chongqing Jiangshuiyuan Heat Pump Energy Saving Technology Co., Ltd., said the system can reduce energy consumption by about 30% compared with conventional central air-conditioning systems while helping mitigate the urban heat island effect.

Beyond technological cooling solutions, Chongqing has been steadily improving its public cooling services. The city has also opened 158 free cooling zones​ in rail transit stations, providing rest areas, drinking water and heatstroke prevention medicines.

Yangzhou was recognized by the United Nations Environment Programme for integrating climate adaptation into urban planning through sponge city infrastructure, rainwater gardens, permeable paving and restored wetlands, helping reduce the urban heat island effect.

From early warning systems to greener infrastructure, cities are exploring ways to reduce heat risks and protect residents in an increasingly warmer world.