The impact of human pollution: Megacities

Tokyo, Japan. Cairo, Egypt. Paris, France. Lima, Peru. What do all of these cities have in common?

They are all megacities - cities with more than 10 million inhabitants. Today, there are more than 30 megacities all over the world. When millions of people live together in a relatively small space they face some unique challenges. In megacities, one of the biggest challenges is managing different types of pollution. A common feature of megacities is that they grow over a very large area, often in a disorganized way.

This is called urban sprawl, and it can cause serious pollution problems. Why? Well, it means that people who live ‘in the city’ might actually live hours away from where they work. Even if there is a public transportation system, it might not extend into every area, so more people depend on cars to get around. Cars release exhaust gases containing thousands of tiny, hazardous substances.

These gases are one of the main causes of air pollution in megacities, along with pesticides, factory emissions, construction, and coal burning. Sometimes the air is so filled with a dense fog formed by pollutants — smog — you can’t breathe well! And when we inhale smog, the risk of respiratory diseases — like asthma — increases. Air pollution is bad for human health, and for the environment, too. Smog travels with the wind...

Exhaust gasses released into the air, damage the earth’s ozone layer and are a major part of why the climate becomes warmer. Since megacities are so large, their air pollution can have a big impact. When a city grows at a manageable rate, there is time to plan roads, sewers, water treatment facilities, schools, etcetera. But cities around the world are increasing by an estimated one million people… per week! And some megacities are growing way too fast to keep up...

Without infrastructure in place to provide for their basic needs, sometimes residents are forced to improvise with makeshift buildings, roads, and sewers. This can lead to the development of slums. Slums are residential areas that are overcrowded and have generally unsafe and unsanitary living conditions. Slums don’t always have city services, like electricity and waste management. Dumping waste in the street or burning it are common, but have potentially dangerous side-effects.

Some garbage, such as plastic, releases toxins when it’s burned. Inhaling this can be poisonous to humans, while waste in the environment can be dirty and make people sick. Today, approximately 1 in 7 people all over the world live in slums. So there are different kinds of pollution. Some of it we can see, like exhaust coming out of an old car, or garbage on the ground.

But what about those annoying honking horns, or the blasting from construction sites? Too much noise can cause noise pollution. Hearing loud noise all the time can be bad for our health, causing hearing loss or sleep disorders. It can affect wildlife too. Many animals rely on sound to find food and avoid predators.

Noise pollution makes this difficult, so animals living in areas taken over by megacities are forced away from their habitats. Despite these problems, megacities are here to stay… The UN estimates that there will be 43 megacities by 2030. As megacities grow, urban planners, governments, and residents will need to keep the health of people and the environment in mind, finding ways to make megacities sustainable…