Air pollution is now a global problem that affects all cities large and small around the world. Countries that are rapidly industrializing, such as China, India, Brazil and Mexico, are among the most affected, as you can see on this world map of air pollution in 2013.
Emerging countries which are catching up with the West will keep on growing fast in the years and decades to come. Today, 3 new cars are sold every 2 seconds in China, adding up to 17.2 million new cars on the roads per year!
Urbanization is growing extremely fast in emerging countries — and yet it’s just the beginning: in China, cities became more populated than the countryside only in 2011 whereas it had been the case in Western countries since the late 19th century. Thus, in the coming decades, 350 million Chinese (more than the entire US population!) will come and settle in cities. Population growth has already lead urban expansion beyond the 4th, 5th and now 6th ring road of Beijing over the years (see the map below). This growth has benefited the local population but also created environmental
problems, impacting health and quality of life.
At a global level, 54% of the world population now lives today in urban areas, a number expected to rise to 66% in 2050. This worldwide urban migration will increase air pollution because of the growing use of cars, heating and air conditioning. While air pollution is sometimes already hazardous in some cities (you can track what you breathe in your city with the Plume Air Report) it is really urgent to find sustainable solutions. How can we make our cities breathable again despite the growing pace of urbanization?
One possible solution is the creation of large-scale vegetalized areas on building rooftops, or ‘green roofs’. Indeed, urbanization leaves almost no space for the creation of green spaces, especially in densely populated cities like Mexico City, Shanghai and New Delhi. But roofs of buildings, which are most often not used at all, could be transformed into green areas. According to a recent study, the total surface area available for green roofs in a city like Beijing is about 100 million square meters.
For instance, official government buildings could easily be used. The constructions of new neighborhoods in the suburbs could directly include green roofs at the top of buildings. According to the same study, this represents an investment of almost $5 billion for a city like Beijing. Certainly a large sum — but a bargain when taking into account the cost of air pollution in China, which has been estimated to $US300 billion a year!
Green roofs would allow Beijing to reduce pollution by particulate matter — the infamous PM2.5 — by 880 000 kg per year, about the same as removing 730,000 cars from the roads of the city! Moreover, this would result in a yearly average temperature reduction of 0.32°C, which would decrease the risk of smog formation by ozone accumulation — which is made worse by high temperatures.
These solutions are not limited to China: in Mexico City for example, the government has already invested over a million dollars to create green rooftops in 2014 in order to reduce pollution.
Green roofs can help make our cities more breathable and livable. They are an efficient, relatively simple to implement, and scalable way to reduce air pollution. And why not also green roofs inParis, London, Hong Kong and in your city?
Food for thought: here’s an interesting article to know more about green roof policies in China.