address warming of cities
Image credit: United Nations via Twitter

The UN Environment Programme (UNEP) has published detailed guidance to help the world’s cities address warming, which is occurring at twice the global average rate in urban areas.

Prepared with RMI, Beating the Heat: A Sustainable Cooling Handbook for Cities states that by the end of this century, many cities could warm by as much as 4°C if greenhouse gas (GHG) emissions continue at high levels. Even at 1.5°C of warming, 2.3 billion people could be vulnerable to severe heat waves. 

Launched at the ongoing UN Climate Conference (COP26) by the Cool Coalition, UNEP, RMI, the Global Covenant of Mayors for Climate & Energy (GCoM), Mission Innovation and the Clean Cooling Collaborative, the new guide offers planners an encyclopedia of proven options to help cool cities.

Have you read?
Three tips for cooling your roof for energy efficient home

“Science tells us that to keep global temperatures from rising by more than 1.5°C, we need to achieve net-zero emissions by mid-century. Sustainable and equitable urban cooling must be a part of cities’ efforts to reach net-zero energy targets,” said UNEP Executive Director, Inger Andersen.

In outlining the problem, the Sustainable Cooling Handbook for Cities described how cities are warming quickly due to the “heat island effect”, caused by a combination of diminished green cover, the thermal properties of the materials commonly used in urban surfaces and waste heat from human activities.

According to the handbook, demand for space cooling is increasing, with the energy requirement for space cooling predicted to triple from 2016 to 2050 as millions of households in developing countries acquire air conditioners in the coming decades.

A guide to address warming efficiently and equitably

The guide notes that the impacts of urban heat are not evenly distributed. Lower-income districts and communities are usually the most vulnerable to heat, placing the negative impacts of excess warming disproportionately on those least likely to be able to afford or access thermal comfort. According to the handbook, cooler cities, homes and streets are key to ensuring climate justice.

The benefits of sustainable urban cooling as laid out are improved health and productivity, reduced power energy requirements, lower emissions and economic benefits.

Have you read?
Study shows the power of passive cooling technology

Cooling strategies can be optimised to work together efficiently. The report calls for a whole-system approach – that is, reduce heat at urban scale, reduce cooling needs in buildings and serve cooling needs in buildings efficiently – to benefit from integrative effects.

CEO of RMI, Jules Kortenhorst said: “Based on systems-level thinking, this handbook includes actionable guidance to help cities make progress towards sustainable and equitable urban cooling, while also cutting emissions and increasing city resilience.”

Supporting case studies

The guide makes use of 80 supporting case studies and examples to demonstrate the effectiveness of the strategies outlined to help cities find an approach to address warming that is best suited to their unique contexts.

  • United States: Heat reduction services from urban tree cover in the United States are estimated to be worth $5.3 billion to $12.1 billion annually. Globally, investing $100 million annually in street trees would give 77 million people a 1°C reduction in maximum temperatures on hot days.
  • Seoul, South Korea: An effort to restore the Cheonggyecheon stream that runs through the city replaced 5.8km of elevated expressway that covered the stream with a mixed-use waterfront corridor. It decreased temperature by 3.3°C to 5.9°C compared to a parallel road a few blocks away, as well as reducing air pollution, noise and car traffic.
  • Medellín, Colombia: Green corridors were created that follow and restore the geography of the area prior to recent development. From 2016 to 2019, the city created 36 corridors, 18 along major roads and 18 along waterways, covering over 36 hectares. The areas with green corridors have already seen temperature reductions of up to 4°C.
  • Paris, France: Paris is home of the first and largest district cooling system in Europe. When the water temperature in the Seine River that cuts through city is below 8°C, this water is used to provide “free cooling.”

Have you read?
Paint with cool surface technology to save energy – SANEDI

In collaboration with the Cool Coalition, the Extreme Heat Resilience Alliance, an initiative of the Adrienne Arsht-Rockefeller Resilience Centre (Arsht-Rock) at the Atlantic Council, announced plans to disseminate the handbook to their partner cities and counties– including Athens, Greece, Freetown, Sierra Leone, and Miami-Dade County, United States. Vietnam will also pilot the handbook in three cities – Can Tho, Tam Ky and Dong Hoi City. Similarly, 10 Indian cities will collaborate with UNEP, India’s National institute of Urban Affairs (NIUA), RMI and the Royal Danish Embassy of India to integrate cooling into their city masterplans.