Throughout history, humanity has turned to cooling solutions that work in concert with nature. Returning to these roots would not only be good for the environment – it can also help to beautify our urban sprawl.

As millions of people once again struggle with heat waves in cities around the world, there are lots of lessons we can learn from history about keeping cool. The Roman city-state featured ‘frigidariums’ – large cold pools for people to cool off in. The Egyptians hung reeds across their doorways and windows to cool the wind as it blew in. And the ancient ‘ziggurats’ (essentially roof gardens) of Mesopotamia provided cool, shady places for visitors to escape the blazing Babylonian sun. These and other cooling solutions throughout history make space for nature, working with rather than against our beautiful planet.

Fast forward to 2019 and in our haste to accommodate 3 million more people per week in cities around the world, we seem to have forgotten much of what these ancient civilizations taught us about cooling. Modern city skylines are dominated by steel, glass, and cement, whilst ‘shanty’ towns are typically covered in corrugated iron roofs – materials that act like giant radiators. The ubiquity of air conditioners is noticeable inside and outside of buildings – pumping cold air in and warm air out, in the process heating up local environments.

These dominant construction materials and cooling technologies are helping to keep some people cool. However, they aren’t accessible to all and come at a high environmental price – the stability of our climate. Experts predict that the humble air conditioner could use up 20-40% of the world’s remaining carbon budget. So whilst modern modes of cooling provide instant thermal comfort, ironically these very same modes are warming the planet up. Darwin would not be proud.

Fortunately, not everyone has forgotten how to work with, rather than against, nature as we strive to keep people cool. The city of Medellín in Colombia was recently recognized with a prestigious Ashden Award (supported by the Kigali Cooling Efficiency Program), for efforts to create ‘green corridors’ in the midst of its buildings, transport routes, and plazas. The results provide a beacon of hope – in addition to keeping the temperature a more pleasant 2-3°C lower than normal, the corridors have engaged communities, beautified the otherwise dull concrete sprawl, reduced air pollution, and enhanced biodiversity.

In Singapore, the government embarked on an ambitious ‘garden city’ plan in 1967 with intensive tree-planting and the creation of new parks. As the population grew and buildings got taller, the focus shifted to include skyrise greenery encompassing ‘skygardens,’ vertical planting, and green roofs. More recently, the government introduced the LUSH policy – Landscaping for Urban Spaces and High-Rises. LUSH requires new buildings to offset any loss of nature with new areas of greenery, including on walls and roofs. Parts of the city literally look like the hanging gardens of Babylon and bring with them 2-3°C temperature reductions and the multiple benefits of cooling by nature.


Italy’s ‘Bosco Verticale’ (Vertical Forest) is a pair of residential towers in the Porta Nuova district of Milan. The buildings (365 feet and 260 feet tall) are adorned with some 780 planted trees and countless numbers of plants, altogether integrating about 1,000 different species into the property. Each apartment has its own private garden, which not only looks great, but also filters sunlight to keep temperatures down and cuts down on noise and air pollution. The gardens are watered through a self-replenishing irrigation process and photovoltaic panels on the roof that convert sunlight to electricity.

Despite these success stories, very few governments around the world, at the national or city level, have seized the opportunity for cooling by nature. Significantly more can be achieved to regulate urban heat islands and rising global temperatures by making space for nature in cities. The September Climate Summit in New York presents a key near-term opportunity for countries to commit to more natural cooling in their national cooling plans. This does not, however, mean jettisoning modern cooling, although air conditioning systems need a paradigm shift in energy efficiency and to move away from super-polluting fluorinated gases that can stay in the atmosphere and contribute to climate change for centuries to come. The future of cooling should blend old and new – mixed modes that first aim to minimize heat (for example by making space for nature), and then address residual heat with locally and culturally appropriate, climate-friendly technologies, such as super-efficient air conditioners using natural refrigerants, or by using renewably powered fans.

Aldous Huxley once said, “That men do not learn very much from the lessons of history is the most important of all the lessons of history.” The stability of our climate demands better. We need a renaissance in how we cool our cities by taking lessons from the past and making space for nature. And as with renaissance art, citizens just might marvel at the beauty that can be created in the midst of our urban sprawl.



About the Author

Dan is the Executive Director of Kigali Cooling Efficiency Program