At the ongoing 26th United Nations Climate Change Conference (cop26), the United Nations Environment Programme (UNEP) released the "overcoming high temperature: urban sustainable cooling manual" prepared in cooperation with the Rocky Mountain Institute (RMI) of the United States on March 3, which aims to provide a reference guide to help global urban cooling. The report points out that the rate of global urban warming is twice the global average. If greenhouse gas emissions remain high, the temperature in many cities may rise by 4 ℃ by the end of this century. Even with global warming of 1.5 ℃, 2.3 billion people may be vulnerable to severe heat waves.

Jules coltenhorst, CEO of RMI, said that the report provided a comprehensive and innovative description of sustainable urban cooling methods within a "system wide" comprehensive framework. It includes feasibility guidance to help urban organizations take priority actions to achieve sustainable and equitable urban cooling, as well as guidelines to reduce emissions and improve urban resilience.

"Science tells us that in order to prevent global temperatures from rising by more than 1.5 ℃, we need to achieve net zero emissions by the middle of this century. Sustainable and equitable urban cooling must be part of cities' efforts to achieve the goal of net zero energy," said Inge Anderson, executive director of UNEP.

The report describes how cities are warming rapidly due to the "heat island effect". "Heat island effect" is caused by the reduction of green vegetation, the thermal properties of common materials on urban surface and the waste heat generated by human activities.

The report noted that the demand for space refrigeration was increasing. As millions of households in developing countries buy air conditioners in the coming decades, the energy demand for space refrigeration is expected to triple from 2016 to 2050.

The report says the impact of urban heat is unevenly distributed. Cool cities, homes and streets are the key to ensuring climate justice. Low income areas are usually the most vulnerable to high temperatures, and the negative effects of excessive warming have a disproportionate impact on those who are least likely to afford or obtain thermal comfort. We need to transition to a more equitable and sustainable way to "cool" our cities and make them suitable for all.

At the same time, the benefits of sustainable urban cooling are far-reaching, including improving health and productivity, reducing electricity and energy demand, reducing emissions and bringing economic benefits.

In addition, the report also calls for a system wide approach, that is, reducing heat and meeting the cooling needs of buildings in cities, so as to benefit from the comprehensive effect.

It is worth noting that in the cooling cases of six cities mentioned in the report, it is pointed out that as one of the measures to build a green and environmentally friendly modern urban center, Guangzhou municipal government of China adopts regional centralized cooling in the development core area of Zhujiang New Town, which reduces the local ambient temperature of the area by 2 ℃ - 3 ℃ compared with the distributed cooling system.