Question

Urbanization and the Environment
Imagine walking down a city street jam-packed with pedestrians. You can’t take even the smallest step without treading on another person. Picture trying to squeeze onto a sardine-stuffed subway during rush hour. Then, a station attendant literally pushes your back through the doors so more people can fit inside. Paint in your mind one of the smallest apartments in the world. It’s only 86 square feet in size and so narrow that you can’t stretch your arms out from side to side.

These aren’t isolated instances or fictional accounts from the mind of a fantasy writer. These scenarios accurately describe the experiences of billions of people around the world who live in densely populated cities. And the numbers are continuing to grow as urbanization becomes more commonplace around the planet. Just six decades ago, only 746 million people lived in urban areas. Today more than half of the Earth’s 7.7 billion population lives in cities. The United Nations expects that number to continue to climb. Experts estimate that by the year 2050, about 68 percent of the people on Earth will be urbanites.

Negative Effects
If cities aren’t constructed and managed properly, they can have a negative effect on the natural world. Air, water, and land pollution is a natural result of millions of people crammed into small spaces. Wildlife is also negatively affected by urbanization. As cities expand, animals lose their habitat or succumb to the effects of pollution. Cities affect Earth’s weather systems, too. Urban areas create a phenomenon known as heat islands. They trap heat and atmospheric pollutants. As a result, cities tend to have 5 to 10 percent more precipitation than nearby rural areas. This shift in weather patterns has two results. First, it can cause drought conditions in rural regions which affects nearby farms. Second, it can increase flooding in cities. Most urban land is covered in concrete or asphalt. Both kinds of surfaces prevent precipitation from seeping down into the soil.

Protection Through Legislation
Humans can combat some of the negative impacts of urbanization. For instance, people can encourage more legislation focused on the natural world. In the United States, the Environmental Protection Agency (EPA) was established in 1970 to help protect the nation’s environment.

One of the first pieces of legislation passed by Congress to be regulated by the EPA was the Clean Water Act of 1972. In the early 1970s, two-thirds of this nation’s rivers, lakes, and coastal waters were unsafe for fishing and swimming. These waters were heavily polluted by untreated dumping of industrial waste and municipal sewage. The goal of the Clean Water Act was to “restore and maintain the chemical, physical, and biological integrity of our nation’s waters.” The EPA continues to do that job today and is also responsible for monitoring air and land resources.

Private–Public Partnerships
Private citizens and businesses can help protect the environment. It takes a community to build a city and also to keep a city clean. Private–public partnerships can help provide needed services like waste disposal and transportation improvement. For example, many large cities have bike and scooter share programs—many of which are operated by private companies. These clean-energy transportation systems allow people to get from place to place without adding pollution to the atmosphere.

Green Spaces
Proper city planning is also important. Cities are often referred to as "concrete jungles." But cities that are the most livable also have plenty of green space. This helps reduce the environmental impact of a city by reducing the overall temperature of the urban space, thus preventing flooding and other weather-related issues. It also helps improve the overall quality of urban life. Just ask anyone in New York City what they would do without Central Park and other green spaces. Their enthusiastic response will reveal the great importance of these spaces for urban dwellers.

Central Park in New York City. A large rectangular area of trees, grass, and ponds are surrounded by skyscrapers.
New York’s Central Park is an oasis in a landscape of concrete, steel, and glass.
Cities will continue to grow as more people move in from the suburbs in what is dubbed by many as the urban explosion. Yet, if people take a more thoughtful approach to city planning and development, it’s possible to sustain quality of life for urbanites and protect the planet at the same time.

Explain why urban explosion is a concern in regard to environmental science.

Answer 1

“Urban explosion” — rapid growth of cities and urban populations — is a major concern for environmental science because it profoundly alters natural systems, increases pollution and resource demand, and creates feedbacks that worsen local and global environmental problems. Key reasons:

- Large increases in pollution
- Concentrated human activity in cities raises emissions of air pollutants (smog, particulates) and greenhouse gases (CO2, methane) from transportation, industry, heating/cooling and power generation.
- Urban waste streams (solid waste, sewage, industrial effluent) overload treatment and disposal systems, degrading rivers, lakes and coastal waters.

- Loss and fragmentation of habitat and biodiversity
- Expanding urban areas replace forests, wetlands and farmland, destroying habitat and isolating wildlife populations. Many species decline or disappear as a result.

- Altered hydrology and increased flooding
- Impervious surfaces (concrete, asphalt, rooftops) stop rainfall from infiltrating the soil, increase runoff, overload storm drains, and raise flood risk. At the same time, changes in urban precipitation patterns can contribute to droughts in surrounding rural areas.

- Urban heat island and local climate effects
- Cities trap heat and pollutants, raising local temperatures (urban heat islands). This affects energy demand (more cooling), human health (heat stress), and local weather patterns (the passage notes cities can get 5–10% more precipitation than nearby rural areas).

- Greater resource demand and infrastructure strain
- High-density populations require large, continuous supplies of water, energy, food, and materials. Rapid growth can outpace infrastructure, causing water shortages, unreliable sanitation, and greater land use pressures nearby.

- Soil and land degradation
- Urban expansion and pollution degrade soils, reduce agricultural land availability near cities, and can leave contaminated brownfields that are costly to remediate.

- Public health and environmental justice issues
- Polluted air and water, heat exposure, and inadequate sanitation disproportionately impact disadvantaged communities, creating social as well as environmental problems.

- Amplified contribution to global change
- Concentrated emissions and energy use in cities contribute substantially to climate change and to alterations of biogeochemical cycles (carbon, nitrogen), with global consequences.

Why this matters to environmental science:
- Environmental science studies how natural systems function and respond to human pressures. Urban explosions change ecosystem structure and function at local to global scales, producing complex interactions (pollution ↔ health ↔ infrastructure; land-use change ↔ hydrology ↔ biodiversity) that scientists must understand and manage.
- Rapid urban growth increases the urgency of designing sustainable cities that minimize ecological damage, preserve ecosystem services, and reduce emissions.

Brief note on responses:
- Effective policy, planning and technology (e.g., environmental regulation, green spaces, permeable surfaces, public transit, waste management, energy efficiency) can reduce many of these impacts — but they require coordinated action at municipal, national and international levels.