Global-Scale Pollution (Part 1): How Does Construction Industry Contribute to Global Warming?

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Nothing is better than waking up and taking a deep breath of fresh air. We accept clean air for granted and assume it will always be there for us. Most of us breathe without thinking about it or even realising we are doing it because it has been part of our life since birth. Nowadays, our air is no longer clean. Atmospheric concentrations of both natural and man-made gases have been rising over the last few centuries due to Industrial Revolution. Buildings and construction are among the top sectors that contribute the most greenhouse gases globally.

Therefore, understanding the overall big picture of this global-scale pollution is essential. I divide this topic into four articles or parts. Part 1, which is this article, explains how the construction industry is responsible for global warming. Part 2 presents the basic science of global warming or how it occurs, followed by a discussion of how global warming affects us in Part 3. Finally, Part 4 describes ozone layer depletion, its causes, and how it differs from global warming.

Air that we breathe

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The air, or the atmosphere, comprises three leading gases: nitrogen (N), making up 78%; oxygen (O2), 21%; and argon (Ar), 0.9%. The other 0.1% of gases include varying amounts of carbon dioxide (CO2), methane (CH4), ozone (O3) and helium (He). There is also water vapour (H2O) in the atmosphere, ranging from 4% in tropical areas to 1% in more arid or desert areas.

Why is it important to understand this composition and how it changes? 

Because it determines the atmosphere's ability to transmit sunlight and trap infrared light, leading to long-term climate changes. Although greenhouse gases (GHGs) comprise a tiny percentage of the atmosphere, they considerably affect the Earth's temperature and global energy balance.

We inhale O2 and exhale CO2. Plants have a reverse process using photosynthesis to absorb CO2 and emit O2. This system of interactions between air, plants, and animals is necessary for survival and provides a balancing feedback loop. When one of the elements in the feedback loop changes, the system is under stress. The system now is indeed under stress. Over the last few centuries, the atmospheric CO2 and other GHGs have risen. 

So what are GHGs?

There are direct and indirect GHGs.

Direct GHGs cause regional-scale air pollution

Direct GHGs contribute to air pollution at the global scale as they serve to increase global warming and hence, climate change. Direct GHGs can be grouped into two categories: natural and man-made. 

Natural GHGs: Many GHGs, such as CO2, CH4, nitrous oxide (N2O), and H2O, occur naturally in the atmosphere. Because the planet is 2/3 covered by water, the average H2O content of the atmosphere depends on temperature. This natural GHG increases in volume with warmer temperatures. 

Man-made GHGs: Direct GHGs that are man-made, synthetic or anthropogenic include hydrofluorocarbon (HFCs), perfluorocarbon (PFCs), and sulfur hexafluoride (SF6). HFCs are considered new. They were developed to replace chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) because CFCs and HCFCs emissions deplete the ozone layer. Although HFCs do not deplete the ozone layer, they cause another problem, which is global warming.

To know more, read "Global-Scale Pollution (Part 4): How Does Ozone Layer Depletion Differ from Global Warming?"

Humans have added 31% more CO2 to the atmosphere since the Industrial Revolution, 60% more CH4 and 17% more N2O. In 2016, humans emitted 36 gigatons of GHGs, 2.3% more than the previous year. This amount is equivalent to 14.4 million Olympic-size pools.

A monitoring station in Hawaii has been recording CO2 levels since 1958. The graph below shows a steady rise since measurement began. CO2 concentration measured in Hawaii does not mean it remains in Hawaii. Once we release CO2 into the air, the atmosphere mixes and spread it evenly around the globe. That means if we measure CO2 in one place, the reading can accurately reflect the CO2 concentration worldwide. 

Atmospheric CO2 concentration measured in Hawaii between 1958-2006

Indirect GHGs cause regional-scale air pollution 

Another category of gases is indirect GHGs like nitrogen oxides (NOx) comprised of nitrogen monoxide (NO) and nitrogen dioxide (NO2), sulfur dioxide (SO2) and carbon monoxide (CO). These gases are not GHGs that can cause global warming. They will only contribute to global warming when they go through some reactions with other chemical compounds and produce direct GHGs as a result of those reactions.

For example, CO2 is oxidised to produce CO2. NO2 and CO2 can also go through some reactions and cause acid rain. So these indirect GHGs contribute to air pollution at a regional scale, not a global scale like direct GHGs.


Where are these emissions coming from?

CO2 is produced by burning fossil fuels, burning of forest lands, deforestation, and mining. Coal, petroleum and natural gas are fossil fuels created from the slow decomposition of plants and animals that existed millions of years ago. After processing, they can all be burned directly to make heat and energy or burned in a power plant and converted into electricity. 

Power generation is a significant contributor to man-made CO2 emissions - and in fact, electric power generation is the greatest source of CO2 to the atmosphere. But it's nearly impossible to avoid generating CO2. Transportation, industry, petroleum production, and even agricultural practice usually burn fossil fuels to function. 

For many years, oceans, forests, plants, trees and soil had absorbed half of the CO2 we spewed out. Now, a few forests are left, mostly logged or consumed by wildfires. Half of the world's tropical forests have been cleared, and about 12 million more hectares are lost yearly. An article by John Vidal published in Guardian in 2017 stated that in nearly 40 years, at the current rate, 1 billion hectares could be gone - a land mass equivalent to Europe. If that is not enough, the permafrost is bleaching GHGs into an already overburdened atmosphere.

Damaged nature in a deforestation area
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CH4 is produced when organic material decomposes at landfills and during the production and transport of fossil fuels. It is also emitted through livestock farming, fossil-fuel burning, wastewater treatment and other industries. In large-scale farming, liquid manure is stored in massive tanks that emit methane. Dry manure left on fields, by contrast, does not.

N2O is emitted when fossil fuels and solid waste are burned from certain agricultural and industrial processes and during wastewater treatment. 

HFCs are released into the atmosphere during manufacturing processes and through leaks, servicing, and disposal of equipment in which they are used; for example, refrigerants (air-conditioning in buildings and vehicles), aerosol propellants, foam-blowing agents, solvents, and fire retardants. 

PFCs are byproducts of aluminium production, and SF6 is released through industrial activities like aluminium smelting, semiconductor manufacturing, and the electricity grid that lights up our cities.

Is the building and construction industry guilty?

Definitely. Based on data in 2016, the manufacturing and construction sectors contributed the most GHGs globally at 24%, followed by road transportation at 12%, residential buildings at 11% and commercial buildings at almost 7%. These sectors are considered the most energy-consuming sectors in the world.


The building sector is one of the largest energy-consuming sectors and a major contributor to climate change.
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The primary source of GHG emissions from buildings is energy use, consumed during all stages of the building life cycle. Raw materials are extracted and manufactured into building materials, transported to the site and put together during construction until the building is under operation and maintenance, then renovation, and finally demolished at the end of its useful life and recovery or disposal of its parts. All these stages consume energy somehow. 

What has happened to the extra GHGs we emitted?

Before the Industrial Revolution in the 19th century,  the levels of CO2 in the atmosphere were steady for thousands of years. That is because natural CO2 is not static, not simply sitting in the air. Naturally-generated CO2 is part of a very natural cycle in the atmosphere. That is why the levels remained stable. The carbon on land and in the ocean has stayed in balance. Earth has been able to generate, absorb, and cycle through CO2 naturally for generations.

Now, consider what happens when we add 36 gigatons of CO2 to the air. The Earth is doing its best to absorb 40% of the extra CO2 in the air, but what happens to the rest of the CO2? 

It sits in the atmosphere for 125 years! Furthermore, as mentioned above, once CO2 is added to the air, the atmosphere mixes and spreads it evenly around the globe. That means CO2 released in one region becomes everyone's problem. What is that problem? It is called global warming.

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