Why Is Urbanization Contributing to Pollution?

Over the past several decades, cities worldwide have been growing at a fast pace. Back in 1950, only a small fraction of about 30% of people lived in cities. Fast forward to 2018, and that number has soared to 55%. The bustling streets of urban centers now host over 4.3 billion people, marking a significant shift that occurred around 2007, when the urban population surpassed the rural [1].

Cities have become the economic engines of our world, driving over two-thirds of the global GDP. But this growth spurt hasn’t been all roses. One of the drawbacks is the escalating pollution that casts a dark shadow over these thriving urban landscapes.

For example, water, a precious resource, is now under siege as cities expand. The city lifestyle is consuming up more freshwater resources than rural areas, and it is often at the expense of nearby agricultural lands that need enough moisture to yield produce.

To make the situation harder, the waste generated by the swelling urban population is finding its way into rivers and other water bodies nearby. Water gets contaminated with a cocktail of pollutants ranging from harmful nutrients, pathogens to plastics and chemicals from personal care products. This not only threatens our drinking water supply but also pushes us back on our goals for sustainable cities and clean water for all.

The connection between burgeoning urban growth and pollution is becoming hard to ignore, and with urban population expected to grow even further by 2050, it is crucial we take a closer look at why urbanization is contributing to pollution of the environment and natural resources.

What is urbanization?

Urbanization is a term that has become quite popular in recent times. But when we dig deeper, defining what it means exactly is quite complex and depends on the point of view. The simplest way of explaining it is this one:

Urbanization is the process where more and more people move from rural areas to live in cities. This also includes the growth and expansion of cities to accommodate these people, which leads to more buildings, roads, and other structures being built around and expanding into natural ecosystems or agricultural lands.

Over time, the areas surrounding cities also become more city-like, with more people and businesses moving in. They turn to classic suburban centers, co-dependent upon the bigger city they surround.

Urbanization usually happens because people are looking for better job opportunities, education, healthcare, and other services that are often more available or better quality in cities compared to rural areas.

But when we want to dig deeper, there is not a one-size-fits-all definition of ‘urban,’ as pointed out by the United Nations. The UN gathered data based on how each country defines its urban and rural areas, and that is where the definition gets tricky.

Each country has its own unique way to approach urbanization. Some countries look at the minimum population thresholds, while others focus on population density, infrastructure development, or even employment types. These differing criteria make it challenging to have a universal understanding of the term ‘urbanization.’

For instance, when we look at the minimum population threshold to define urban areas, the disparities become obvious. While some countries set the bar at 2,000 to 5,000 inhabitants to be define urban area, others have a much wider range. Sweden and Denmark consider areas with merely 200 inhabitants as urban, whereas Japan sets a lofty threshold of 50,000 inhabitants. That is a staggering 250-fold difference!

Such a big difference in understanding the term means that your perception or knowledge of urban area may be also affected by your location. In your country, a community of 1,000 people may already enjoy the benefits of a town life with healthcare facilities, restaurants and different cultural events, while somewhere else a community of the same size could be just scattered farms with the need to commute to some larger town for the same services.

From this point of view, even the levels and the character of pollution will differ and will depend upon the regional and national differences.

Why is urbanization contributing to pollution of the environment?

As city population grows, urban expansion inevitably follows suit. This means more space for houses is needed, shops, roads and parking spots, sports centers, and other infrastructure that people need to live and work.

Urban expansion usually has a few effects that happen at any location, and unfortunately, inevitably lead to pollution of the environment. Firstly, as the city spreads, it often takes over fields, forests, and other green spaces. This means there is less space for purifying plants and wildlife, thus removing the ecosystem services from the equation.

Secondly, more people mean more traffic. This leads to longer travel times due to congestion and even more pollution. With more people and cars, pollution usually goes up. Let’s have a look at the situation closer.

Air pollution due to traffic linked to urbanization

A big part of city expansion is the increasing number of vehicles on the roads, fueling the daily commutes and lifestyle demands of the urban population. Cars, buses and trucks make our daily travel and city life support easier. But there is a downside. The exhaust from all these vehicles inevitably pollutes the air.

This is not just happening in huge cities around the world, but even smaller towns see more cars on their roads as they get busier over time.

The transport industry accounts for 29% of greenhouse gas emissions in the United States [2].

The exhaust from cars is a cocktail of various pollutants, including carbon monoxide, nitrogen dioxide, particulate matter, carcinogenic benzene, and formaldehyde, all of which contribute to deteriorating air quality. Rising concentrations of these pollutants leads to numerous problems – from adding to the dirty haze that often hangs over cities to pumping out greenhouse gases that worsen climate change.

The thick smog doesn’t just hide the city views but can also be bad for our health, especially for those who already live with chronic lung conditions. Over time, breathing in this dirty air could possibly shorten lives and make urban living less enjoyable due to frequent exacerbation.

For instance, the World Health Organization estimated that air pollution led to 6.5 million deaths globally in a single year, representing 11.6% of all global deaths, a statistic that resonates with alarming clarity.

Places like Mexico City, Beijing, and Shanghai, along with major industrialized regions like the Ruhr Basin in Germany, are now prominently featured on global air pollution maps, indicating severe pollution levels. For instance, the global distribution of nitrogen dioxide (NO₂) in the troposphere clearly identifies these areas as severely polluted regions, dangerous for health.

Industrial growth around urban centers and air pollution

Cities draw in industries because they offer a large pool of workers, good infrastructure, and a network of other businesses. The more industries come into a city, the more people move in for jobs. However, this growth has a downside: air pollution. The smoke from chimneys and exhaust from trucks delivering goods contribute to dirty air we often breathe in industrial areas.

Some industries are worse than others when it comes to spewing toxic emissions. For instance, oil refineries, steel plants, and chemical factories tend to release a lot of pollutants into the atmosphere.

Oil refineries turn crude oil into gasoline, diesel, and other products. This process involves burning off impurities, which releases gases and small particles into the air. Common pollutants from refineries include sulfur dioxide, nitrogen oxides, and volatile organic compounds which can react with sunlight to form ground-level ozone, a key component of smog.

Making steel requires high temperatures, often achieved by burning coal or coke (a type of carbon). When coal burns, it releases sulfur dioxide, nitrogen oxides, and particulate matter. These emissions are harmful to human health and can also contribute to hazy skies around steel plants.

The production of chemicals releases a variety of volatile organic compounds, nitrogen oxides, and sometimes heavy metals like mercury or lead.

Among pollutants, tiny particulate matter known as PM₁₀ and PM_2.5 are a major concern. These particles can carry heavy metals and get breathed in deep into our lungs and enter our blood stream. They are linked to around 3 million deaths worldwide every year and cause serious health problems like heart disease, stroke, and cancer.

The growth of cities since the Industrial Revolution brought many jobs and opportunities, but also a serious challenge in dealing with air pollution. Some areas have been able to deal with this burden by implementing effective measures as years went by.

For example, a look at northwest England shows a shift in its pollution profile over the years due to industrial activities. After 1990, as more industries and power plants popped up alongside urban sprawl, pollution got worse. Luckily, by 2000, some areas like Merseyside saw a reduction in pollution due to better regulations. Unfortunately, the same scenario doesn’t always happen. Many industrial regions only see heavier burden due to faster industry growth.

Urbanization causes water pollution & wastewater overload

When it rains, water rushes over roofs, roads, parking lots and other impermeable surfaces so plentiful in cities and picks up debris and accumulated substances. The stormwater pollutants are often motor oil, but even physical objects like cigarette butts, metals, and plastic litter. Other common materials that occur in city landscapes are pesticides, herbicides, fertilizers from gardens, bacteria from pet waste, failing septic system wastewater, detergents and chemicals from automotive maintenance and repair.

The problem is bigger than you may think. For example, a single motor oil change can taint up to one million gallons of freshwater if done without consideration for the water resources protection. In the United States alone, around 193 million gallons of used oil are wrongly dumped every year. That equals 17 Exxon Valdez oil spill events every year [3].

The contaminated stormwater then enters drainage systems that directly lead to rivers, lakes, or the ocean, without any treatment to remove these harmful pollutants.

The issue of water pollution extends beyond stormwater runoff. Direct discharge from residential and commercial wastewater contribute a significant burden to urban water bodies. As we have written in our detailed article on water pollution causes, each year 860 billion gallons overflows from sewer systems across America, and it is mainly because the many of the wastewater management systems that are in place are old and lack the capacity to serve their growing population base.

Industries pollute water in urban areas

The manufacturing of numerous goods inherently produces wastewater often laced with toxic substances. While regions like Europe have strict regulations, this is not the universal case. Particularly in emerging economies such as China, India, and some countries in Africa and South America, the exponential industrial growth hasn’t been paired with adequate environmental policies.

As a result, untreated industrial wastewater finds its way into public waters daily. But cases against could be found everywhere. For instance, despite having laws against water pollution, a 2009 study revealed that in the USA, 44% of assessed streams, 64% of lakes, and 30% of bays and estuaries were classified as polluted by our activities [4].

The ramifications of industrial wastewater discharge are far-reaching and alarming. The hazardous substances, many of which are difficult to biodegrade, accumulate in water sediments. The contaminants cause illnesses and fatalities among fish, crustaceans, and other aquatic creatures.

In extreme scenarios, pollutants seep through the ground, contaminating the groundwater which eventually mingles with drinking water. An example is chlorobenzene, a carcinogenic compound used in various industries (e.g. organic chemicals production, paints, dry cleaning), which not only ended up in drinking water but also accumulated in human fatty tissues and liver.

The pharmaceutical sector often releases wastewater filled with active ingredients like antibiotics and hormones, while the metal processing industries may contaminate water with heavy metals.

Land pollution due to urbanization

When cities spread, they take over vast areas of farmed and natural lands, which results in the loss of fertile and permeable soil. The World Bank mentions that cities produce about 2.01 billion tons of waste every year. In many situations, a portion of this waste ends up on the land and leads to land pollution and soil degradation.

Just imagine how many cigarette butts, old chewing gums and tiny pieces of plastic litter you spot when walking around the busy street. Even this seemingly insignificant debris affects soil quality when slowly decomposing into the ground along the places where we spend our time.

Constant construction work in cities also contributes to heavy metals, chemicals, and building waste contamination of soils. What is a common practice is that this type of pollution doesn’t get cleaned up, ever. It only accumulates as it gets buried by more renovation projects and constant development.

A study in Italy from 2012 to 2020 showed that as cities expand, the land properties (physical and chemical) change, even in a certain distance from the busiest centers. Any of these changes affect natural processes like carbon storage capacity within soil, water cycle due to increase in impermeable surfaces, soil filtering function. Additional impact and even easily overlooked is tipping off the ecosystem services, like pollination disappearance due to changes to vegetation cover.

Urbanization and rising noise pollution

Urban areas are bustling with activities, providing jobs and entertainment. However, all the fuss inevitably results in a noise pollution. This problem is more than just a minor annoyance. It causes serious health issues like long-term sleep problems, problems with concentration, heart diseases, diabetes, increased anxiety and other mental health challenges to city residents.

For instance, a whopping 90% of people using mass transit in New York City face noise levels beyond what’s considered safe. Or cyclists in Ho Chi Minh City deal with noise so loud that it can cause permanent hearing loss – so bad, especially when considering that they are cycling rather than driving emission releasing vehicle.

Sadly, those who live near busy roads and industrial areas, often the young and the elderly from less wealthy communities, suffer the most. In the European Union, noise pollution touches one in five people, leading to 12,000 early deaths every year. It is simply through the production of stress signals in the body, whether asleep or awake, that noise takes its toll on organism. This makes noise pollution a symbol of social and geographical inequality, particularly in poorer countries [5].

But noise doesn’t only affect people, it also disrupts the whole ecosystem in and around cities. Mammals, birds, insects, and frogs find it hard to communicate and behave normally amidst constant noise. This is because animals depend so much on their sense of hearing to survive. These negative impacts affect both domestic animals and wildlife, with pets potentially becoming more aggressive in a noisy environment, and wildlife suffering from hearing loss, an increased vulnerability to predation, or a hampered ability to hunt.

You may find this interesting, though. Luckily, one solution to this problem would be planting more green islands within cities, with trees and shrubs acting as natural noise barriers, cutting down noise by up to 12 decibels in some places.

Urban light pollution getting worse

80% of people on Earth can no longer see the natural night sky due to the bright glow of city lights. The world’s brightest cities, like Moscow and Riyadh, have light pollution levels 8.1 and 6.7 times brighter than the global urban average, respectively.

Too much artificial light can affect our health in many ways, from sleep problems to even increasing the risk of cancer. The artificial lights mess with our body’s natural clock, known as the circadian rhythm, making it hard for us to fall asleep and stay asleep.

Before electric lights, people would go to bed shortly after sunset, getting the quality REM sleep coming naturally before midnight, and would sleep longer in general. Now, the bright lights in cities have changed our sleep patterns, making us stay up later, watching the screens of electronic devices, putting strain on our brains. For example, The International Dark Sky Association is trying to teach people about the importance of dark skies and how to reduce exposure to light pollution. Their work is important and underrated.

Let’s not forget that pollution reaches beyond our sleep patterns. Artificial lights cause trouble for wildlife as well. Scientists looked last year at over 160 different kinds of plants and animals and found that our lights change how they behave.

For example, fireflies use light to find mates, but city lights mess this ability up, putting some firefly species at risk of disappearing. In big cities like Chicago, birds get confused by the bright lights, and they crash into lit-up buildings.

Even leatherback turtles have a hard time. They struggle to come ashore to lay their eggs because of the bright lights blinding them and confusing their navigation sense when looking for their original hatching spot.

These examples show that as we fill our cities with more lights, we are causing unexpected problems for nature, and we need to find better ways to keep our nights dark again.

Habitat loss and land grabbing for urbanization progress

The size of cities is expanding with increasing speed. Unfortunately, this expansion often comes at the cost of natural ecosystems and rural areas in the closest vicinity. For example, between 1992 and 2000, urban expansion led to a loss of about 190,000 square kilometers (73,000 square miles) of habitat, amounting to 16% of total habitat loss during that period [6].

The numbers of native species usually plummet with more intense urban land-use, as they are not welcome anymore and do not have possibilities to find suitable places to live and food to eat throughout the year.

Additional problem that often goes hand in hand with urbanization, are invasive species. They often speed up the disappearance of original flora and fauna, as they are better able to live from resources cities have to offer.

Forecasts reveal a concerning future, with around 290,000 square kilometers of natural habitat projected to be lost to urban expansion until 2030. This urban sprawl is also expected to encroach near protected areas, tripling the extent of urban land in those regions. This could result in fewer unique local species, with 13% of them located in areas expected to be highly affected by growing cities. Additionally, around 8% of the species of land animals listed on the IUCN Red List of Threatened Species are mainly in danger due to city growth [6].

Loss of pristine natural areas for urban expansion harms even people. If we lose connection to trees and animals, we also lose our inner calm, and spend rather too much time in the long-term agitation of our nervous and immune system. We have written an article on this topic, called Find Your Happiness In Nature where we discuss the adverse effects of being deprived of the clean and peaceful natural environment.

Urban heat island effect

The phenomenon known as the heat island effect happens when cities absorb more sunlight and get hotter compared to the nearby countryside. One big reason for this effect is that a lot of city land, about 30 to 45%, is covered with pavements and buildings that soak up a ton of solar heat every day.

Such accumulation of heat can cause city temperatures to rise up to 22 degrees Fahrenheit (12℃) more than in greener areas around them. The U.S. Environmental Protection Agency notes that a city with at least 1 million people tends to be 1.8 to 5.4 degrees Fahrenheit (1 to 3 ℃) warmer than the surrounding rural spots.

The extra warmth in cities from the heat island effect leads to several problems. For one, it pushes up the need for energy as people turn the AC up to cool down their buildings – which then raises energy costs. Energy consumption also boosts pollution and the release of greenhouse gases into the atmosphere, since most energy is still supplied from fossil fuels.

Plus, it is not good for water quality as well. The rising temperatures in the city warm up local waters, which harms water life and makes water less clean in general, as bacteria usually thrives in lukewarm water.

How does urbanization affect the environment in a negative way?

Urbanization, a symbol of modernization and advancement, often comes at a steep cost to both the environment and society. The looming threat of biodiversity loss is exacerbated by cities expanding into forests and agricultural systems, leading to habitat destruction and fragmentation. This, in turn, threatens survival of numerous species, pushing some to the brink of extinction.

Urban lifestyles, characterized by high consumption rates, further strain natural resources and escalate pollution levels across air, water, and soil. Air pollution, propelled by a high concentration of vehicles and industries in urban areas, is a critical concern, with cities like Beijing and Mexico City serving as stark reminders of the severe health hazards posed by polluted air.

Water and soil pollution too, driven by improper waste disposal and excessive use of pesticides and fertilizers, threaten both human and ecological health.

Moreover, the skyrocketing energy demands in urban areas significantly contribute to the global crisis of rising greenhouse gas emissions, fueling climate change. The sheer amount of waste generated in cities necessitates robust waste management systems to avert environmental damage and public health risks. The persistent issues of traffic congestion, noise pollution, and light pollution further deteriorate the quality of urban life.

The loss of green spaces to urban development not only deprives residents of essential recreational spaces vital for mental health, but also intensifies the heat island effect, making cities unbearably hotter compared to nearby rural areas.