资源环境科技发展态势分析平台

The more the planet warms, the more cities are finding they need new ways to keep urban temperatures down and protect their residents. Heatwaves are already by far the deadliest weather-related disasters in Europe; 140,000 deaths associated with 83 heatwaves have been recorded since the beginning of this century. Today, only 8 per cent of the 2.8 billion people living in places with average daily temperatures above 25 degrees Celsius have an air conditioner.

Cooling is particularly important in cities facing rising temperatures, worsened by the urban heat island effect—concrete and tarmac absorbing the sun’s power, radiating it out as heat and keeping the city warm long after the sun has gone down. Waste heat from engines and other energy-consuming equipment in transportation, industry and space cooling make cities even hotter.

Often, poorer neighborhoods are more affected as residents have less access to air conditioners and breezy green spaces, putting vulnerable people at greater risk of heat-related health complications.

The standard solution to cooling in cities is to add more air conditioning, but this brings its own set of problems. Energy-hungry cooling further drives global warming. The number of cooling appliances in use is expected to grow from 3.6 billion today to 9.5 billion by 2050. If air conditioners were provided to all those who need them, not just those who can afford them, there would 14 billion cooling appliances in use by 2050. Emissions would go through the roof.

Many cities, however, are taking bold steps to show that they can keep cool in a sustainable manner, with the Indian city of Ahmedabad chief among them. The city implemented its Heat Action Plan after an extremely hot and deadly pre-monsoon season in 2010. The plan not only set up an early-warning system for the vulnerable. It included water supplies to the public, plants and trees and a “cool roof” initiative to reflect heat. Some 7,000 low-income households have had their roofs painted white, a simple measure that dramatically reduces inside temperatures by reflecting sunlight.

The Heat Action Plan saves an estimated 1,100 lives each year. Its innovative multi-step approach won the 2020 Ashden Award for Cool Cities, which recognizes pioneers in the fight against climate change.

There is a huge body of evidence showing that city-level interventions can greatly mitigate the effects of heat stress. On a typical sunny summer afternoon, a clean white roof that reflects 80 per cent of sunlight will stay about 30 degrees Celsius (55 degrees Fahrenheit) cooler than a gray roof that reflects only 20 per cent of sunlight. The International Energy Agency estimates that well-designed cities could save 25 per cent of the energy they use for heating and cooling.