What Are Greenhouse Gases?

What Are Greenhouse Gases?

Since the industrial revolution began, human activity has increased the emission of greenhouse gases. Many industrial processes our modern world depends on have increased the amount of carbon dioxide and other greenhouse gases in the atmosphere. As a result, global temperatures have risen. Greenhouse gases help keep the earth at a temperature suitable for human life. However, too many greenhouse gas emissions result in global warming. 

The latest report from the Intergovernmental Panel on Climate Change unequivocally attributes a 1.1C rise in global temperatures to human activities1, predominantly increasing emissions of greenhouse gases. And forecasts suggest the trend is a long way from reversing. 

This article answers the question of "what are greenhouse gases?" in detail. Here, you'll understand what constitutes a greenhouse gas and the sources, types, and effects of global greenhouse gas emissions. 

An Introduction to Greenhouse Gases

An Introduction to Greenhouse Gases
Photo: iStock

Gases in the atmosphere that influence the earth's energy balance are greenhouse gases. Greenhouse gases, also known as GHGs, trap heat in the atmosphere. These gases can absorb infrared radiation the surface of the earth emits. Not only do they trap heat in the atmosphere, but they also cause the greenhouse effect.

Furthermore, any gaseous compound in the atmosphere capable of absorbing infrared radiation (IR) or infrared light, thereby holding heat in the atmosphere, is a greenhouse gas. IR is radiant energy that is not visible to human eyes but which we can feel as heat. 

Simply put, the sun shines on the earth's surface during the day to keep the surface warm. The earth's surface cools during the nighttime, releasing the heat back into space. 

Greenhouse gases trap some of the heat in the atmosphere to keep the earth's temperature at an average of 15°C (59°F). Without greenhouse gases, the earth's average surface temperature would fall to about -18°C (0°F). 

Interestingly, without these greenhouse gases in the atmosphere, performing what we call the natural greenhouse effect, the earth would be too cold to live in. 

Greenhouse gases are vital atmospheric temperature regulators. However, excess greenhouse gases harm the climate by trapping more heat than usual. 

Additionally, excess greenhouse gases increase the rate at which the atmosphere absorbs shortwave radiation from the sun. But, this absorption has a much weaker impact on global temperature. 

Examples of greenhouse gases are carbon dioxide CO2, methane CH4, nitrous oxide (N2O), and water vapor (H2O). Most greenhouse gases have natural or manufactured sources.

What Are the Types of Greenhouse Gases?

There are several greenhouse gases in the atmosphere. The main greenhouse gases in the atmosphere are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). Though all these are naturally occurring greenhouse gases, their increasing atmospheric volume is manufactured. 

Fluorinated gases like hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride and nitrogen trifluoride are synthetic and potent greenhouse gases. 

Fluorinated gas emissions share the element of fluorine created during human-made industrial processes. This includes varieties of household, commercial and industrial applications and processes. 

Although they are limited and minute in concentration in the atmosphere, they are potent as they trap heat effectively. Global Warming Potential (GWP) is a measure to compare the impact of other greenhouse gases relative to 1 ton of Carbon Dioxide.

Fluorinated gases have a GWP range from thousands to tens of thousands. Consequently, they are rated high GWP gases because they absorb significantly more heat than carbon dioxide (CO2). 

Water Vapour (H2O)

Water vapor, naturally present in the atmosphere, is also the most abundant greenhouse gas. It increases simultaneously with the earth's warmness. This makes it function as climate feedback and as a mechanism to measure the greenhouse effect.

However, water vapor persists just for a few days in the earth's atmosphere, unlike CO2, which persists for centuries. Whereas we have an excellent atmospheric measure of other greenhouse gases such as carbon dioxide and methane, there's a poor measurement of global water vapor. 

The behavior of water vapor differs from other greenhouse gases because human actions can't directly influence how much water vapor exists in the atmosphere. Instead, the temperature of the air sets it as the warmer it is, the greater the evaporation rate of water from the earth's surface. 

As a result, when the earth experiences an increase in evaporation, it simultaneously increases water vapor concentration in the atmosphere. Water vapor can absorb infrared light and emit it back to the surface. 

Carbon Dioxide (CO2)

Photo by Callum Shaw on Unsplash

Federal agencies and academic researchers consider carbon dioxide the most important greenhouse gas. CO2 occurs naturally and also as a result of human activities. 

The natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals means that C02 is naturally present in the atmosphere.

Carbon dioxide emissions occur naturally via volcanic eruptions, combustion, natural decay of organic matters, and respiration by aerobic (oxygen-using) organisms. The physical, chemical, or biological processes that remove carbon dioxide from the atmosphere are called sinks. Natural sinks, such as terrestrial vegetation absorb CO2 during photosynthesis. 

Human processes, primarily burning fossil fuels like oil and coal, increase atmospheric gases and excess carbon dioxide emissions. Burning secondary natural gas for transportation, heating, and electricity production also contributes to C02 emissions. 

Deforestation through the burning of forests and clearing of land, production of cement, solid waste, and land-use changes lead to the release of carbon dioxide. Deforestation processes release up to 4.8 billion metric tons of carbon into the atmosphere yearly3.

Anthropogenic emissions of atmospheric carbon dioxide are equal to approximately 3% of carbon dioxide emissions by natural sources5. However, humans have caused a skyrocketing increase in the atmospheric concentration of carbon dioxide by 50% since the industrial revolution began. In 2020 in the United States, CO2 made up around 79% of greenhouse gas emissions from human-made sources7, predominately associated with fossil fuel combustion. 

Though carbon emissions come from various natural sources, human-related emissions are responsible for the increased atmospheric CO2 that has occurred since the industrial revolution. Numerous industrial activities that require energy, driving our cars and flying away on holiday all add more carbon dioxide to the atmosphere. Additionally, they influence the ability of a natural sink, like a forest, to remove CO2 from the atmosphere. 

Human activities 20,000 years before the industrial revolution made atmospheric CO2 fluctuate between 180 parts per million (ppm) during the ice ages and 280 parts per million (ppm) during the warm interglacial periods. 

As of May 2022, the CO2 level stands at 418ppm. Owing to its abundance, CO2 is the main contributor to climate change. Its contribution to climate change and global warming percentage (GWP) is heightened by the projected continued growth in emissions and atmospheric concentration. Also, the fact that CO2 stays can last for over a century in the atmosphere is of great concern. Predictions have it that this trend will persist.

While studies show that methane and other greenhouse gases trap more heat than CO2, scientists still consider carbon dioxide the dominant greenhouse gas. Its global warming effect outlives the effect of others by centuries. 

Methane (CH4)

Researchers have estimated that livestock may contribute up to 2% to global warming6 largely due to methane emissions associated with digesting their food stocks. Photo by Megumi Nachev on Unsplash

Methane, a hydrocarbon gas, is the second most important greenhouse gas. This greenhouse gas comes about naturally through waste decomposition in landfills, the decay of organic waste, agriculture, land use, ruminant digestion, and livestock manure management. 

Also, methane emissions occur during human activities involved in producing and transporting coal, natural gas, and oil. 

Human activities have displaced the natural balance. Research indicates that human activities now account for 50-65% of total methane emissions8. This primarily comes from industry, agriculture, and waste management activities.

Further, methane is very potent but is far less abundant than CO2 in the atmosphere. Methane will comprise 11% of US greenhouse gas emissions in 2020. It's about 20% more potent than CO2 but oxidizes to CO2 after about a decade in the atmosphere. 

Methane traps radiation 21 times more efficiently than carbon dioxide, meaning it has a higher global warming percentage rating. On a molecule-for-molecule basis, methane is a far more active greenhouse gas than carbon dioxide. It's, however, far less abundant in the atmosphere than carbon dioxide. 

A sudden increase in the concentration of methane in the atmosphere was responsible for the warming event that raised global temperatures by 4-8°C (7.2- 14.4°F) on average roughly 55 million years ago during the Paleocene Eocene Thermal Maximum (PETM).

Nitrous Oxide (N2O)

Nitrous oxide also occurs naturally in the earth's atmosphere as part of the nitrogen cycle. N2O emissions also come from agriculture and land use, while industrial activities like the combustion of fossil fuels and solid waste and water treatment processes also play a role.

Nitrous oxide is an effective GHG produced by the cultivation of soil practices, primarily commercial and organic fertilizers. It can also be born while producing nitric acid and burning biomass. 

Human activities take the lead in increasing the atmospheric concentrations of nitrous oxide. It accounts for 7% of greenhouse gas emissions in the US.

Nitrous oxide molecules live for about 120 years in the atmosphere before a sink removes them or chemical reactions destroy them. A pound of nitrous oxide will warm the globe 300 times more than a pound of carbon dioxide.  

Ozone (O3)

Ozone occurs naturally at higher elevations in the atmosphere (the stratosphere). Here, it blocks ultraviolet (UV) light, harmful to plant and animal life, from reaching the earth's surface. The protective benefits of stratospheric ozone outweigh its contribution as a greenhouse gas which is why people don't often consider it a greenhouse gas. However, technically, ozone is a greenhouse gas. 

Ozone is helpful or harmful depending on its position in the earth's atmosphere. Surface ozone results from air pollution, while naturally-occurring stratospheric ozone helps balance the amount of harmful light that reaches the earth's surface from the sun.

The primary natural source of surface O3 is the subsidence of stratospheric O3 from the upper atmosphere. In contrast, the primary anthropogenic source of surface O3 is photochemical reactions involving the atmospheric pollutant carbon monoxide (CO). Ozone concentrations rise to unhealthy levels in cities liable to photochemical smog. 

Fluorinated Gases

Additional trace gases from industrial activities that have greenhouse properties include fluorinated gases (halocarbons). These include: 

  • Chlorofluorocarbons (CFCs),
  • Sulfur Hexafluoride (SF6),
  • Hydrofluorocarbons (HFCs),
  • Nitrogen Trifluoride (NF3), and 
  • Perfluorocarbon (PFCs). 

These greenhouse gases are also referred to as industrial gases. They are synthetic, potent greenhouse gases emitted from various household, industrial and commercial processes, and applications. 

Whereas we can find considerably smaller quantities in the atmosphere compared to other greenhouse gases, their potency is very high, and so is their life span. They are high global warming percentage gases trapping substantially more heat than the others listed above.

Fluorinated gases disperse widely across the globe once emitted into the atmosphere. Only sunlight at the highest level of the atmosphere can remove them from the atmosphere. Fluorinated gases are substitutes for ozone-depleting substances. Their usage is also paramount in the manufacturing process of aluminum and semiconductors. 

Chlorofluorocarbons (CFCs)

CFCs are synthetic compounds that come primarily from industrial processes. Manufacturers popularly use it as a coolant in refrigerators and air conditioners. Other uses include as a propellant in spray cans, as a blowing agent for foam and packing materials, and also as a solvent for industrial purposes. 

However, international agreement regulates their production and release into the atmosphere, with many countries having banned their production entirely apart from a few specialized applications. This is due to their ability to contribute to destroying the ozone layer.

Just as the name implies, chlorofluorocarbon is a compound that only contains carbon, chlorine, and fluorine. It has been in existence for 60 years. Even though they are far less abundant than carbon dioxide in the atmosphere, they are 10,000 times more potent. 

As a greenhouse gas, CFCs can stay in the atmosphere for more than 45-100 years4

Sulfur Hexafluoride (SF6)

Sulfur Hexafluoride (SF6) is an odorless synthetic fluorinated carbon with an extremely stable molecular structure. It's non-toxic, highly stable, non-inflammable, and electronegative. This implies that it will not form other compounds that will alter its state and effectiveness. It's the most potent greenhouse gas known to date. 

Historically, its usage can not be underestimated in a variety of applications, from metal smelting to filing double glazing panels. Electric utilities have relied on it heavily because of its unique dielectric properties. There are also technical challenges in finding a replacement for it. The electrical power system uses SF6 for voltage electrical power insulation, current interruption, and arc quenching in transmitting and distributing electricity. 

Around 80% of the world's SF6 use is in electricity transmission and distribution. Renewable technology also uses this greenhouse gas. For example, switchgear for wind turbines uses it to prevent overloads. Its usage is also in electronics as semiconductor devices in computers, smartphones, consoles, and batteries for electric vehicles.

Once in the atmosphere, it has an atmospheric lifetime of 3200 years. It can accumulate without degrading for millennia to come. Thus, a relatively small amount of sulfur hexafluoride has a significant impact on global climate change. 

Its high atmospheric stability and ability to trap infrared light infer that it dwarfs the potency of CO2 warming the earth's atmosphere over a longer period. An estimate revealed that over 100 years, SF6 has been 23,500 times more effective at trapping infrared radiation than CO2. This implies that 1kg of SF6 has the same impact as 23,500kg of CO2. 

Hydrofluorocarbons (HFCs)

Hydrofluorocarbons are a type of synthetic greenhouse gas with wide use in refrigeration and air conditioning equipment. Furthermore, federal agencies widely use HFCs in a variety of applications, including refrigeration, air conditioning, building insulation, fire extinguishing systems, and aerosols. 

HFCs have a high global warming potential because they trap more heat in the atmosphere than a similar carbon dioxide mass. For instance, releasing 1 tonne of HFC is equivalent to releasing 14,800 tonnes of carbon dioxide. This raises concerns about their impact as industries are increasingly using them as replacements for ozone-depleting substances (ODS). Also, the economic growth and rising temperatures trigger demand for new equipment, especially air conditioners and refrigerators. 

Nitrogen Trifluoride (NF3)

NF3 is a manufactured gas that circulates from the surface to the stratosphere 100 times once in the atmosphere. Solar ultraviolet radiation destroys it. 

NF3 is an inorganic nitrogen fluorine compound that replaces perfluorocarbons (PFCs), specifically hexafluoroethane (C2F6). It has several applications in the electronics industry. Some processes include plasma etching, cleaning chambers in which silicon chips are made, semiconductors, and LCD panel manufacturers. Additionally, its usage is significant within the photovoltaic and chemical laser industries. It is highly effective at trapping atmospheric heat and has a life span of 740 years.

NF3 is nearly chemically inert in the atmosphere. However, it is quite effective in absorbing the infrared light emitted by the earth. Also, NF3 is a missing greenhouse gas because it is not included in the Kyoto protocol list of greenhouse gases. It is a synthetic chemical produced in industrial quantities - although the rapid rise in its production by the chemical industry had gone almost unnoticed. 

Perfluorocarbons (PFCs)

As the name suggests, perfluorocarbon is a manufactured chemical compound that comprises fluorine and carbon only. It belongs to a group of chemically-related greenhouse gases covered by the Kyoto protocol. 

Perfluorocarbons are potent greenhouse gases that were introduced as alternatives to ozone-depleting substances. PFCs replace chlorofluorocarbons (CFCs) when producing semiconductors. Also, the electronic industry uses it as a solvent and as a refrigerant for some specialized refrigeration systems. Furthermore, the release of manufactured fluorocarbons is rising due to increased aluminum and semiconductors chip manufacturing.

The emission of perfluorocarbon compared to other greenhouse gases is low. However, they are of immense concern because perfluorocarbons are extremely powerful greenhouse gases with very long atmospheric lifetimes. 

According to the European Environment Agency, although total emissions of PFCs are relatively small, they are potent greenhouse gases. PFCs are highly environmentally stable, and only the action of oxygen and sunlight slowly destroys them. They are strong absorbers of infrared radiation. While the atmospheric concentration of carbon dioxide is larger than perfluorocarbon, the radiative forces of PFCs, due to the atmospheric loading, are more extensive than that of CO2. 

What Are the Sources of the Major Greenhouse Gases? 

Greenhouse gases make the planet warmer by trapping heat in the atmosphere, thereby increasing global temperatures. Over 150 years, human activities have contributed to significant growth in the production of GHGs. Generating energy to fuel our modern lifestyles, like coal mining and combustion to generate electricity, are significant sources of greenhouse gases. Human-made sources of greenhouse gases include:

Agricultural Practices

Agricultural practices, including farming livestock such as cows, agricultural soil, and rice production, all contribute to greenhouse gas emissions. For instance, methane comes from agricultural practices in the form of livestock manure. 

Studies reveal that livestock is responsible for about 14.5% of global greenhouse gas emissions2. The primary sources of emissions are feed production and processing, outputs of greenhouse gases during digestion by cows (flatulence), and manure decomposition. Also, using fertilizers in agriculture leads to higher N20 concentrations. 

Forestry and Land Use

Deforestation is a primary source of CO2 due to the felling and heating or burning trees to produce goods. This results in the emission of carbon dioxide stored for photosynthesis into the atmosphere. 

Higher concentrations of atmospheric CH4 are also caused by changes in land and wetland use, pipeline losses, and landfill emissions. 

Industrial Activities

Global greenhouse gas emissions from industry primarily come from burning fossil fuels for energy, such as oil-burning or coal-fired power plants. 

It also comes from certain chemical reactions necessary for manufacturing finished products from raw materials. For instance, heating calcium carbonate to produce lime and CO2 in cement manufacturing contributes CO2 to the atmosphere. 

Transportation

Much of our modern transportation causes the emission of greenhouse gases. This occurs by burning fossil fuels for cars, bikes, trucks, ships, trains, and planes. A large percentage of the fuel for transportation is petroleum-based. These include gasoline and diesel. 

Commercial and Residential Activities

Decomposition of waste from both commercial and residential means emits greenhouse gases. Not just the waste, the process of producing goods commercially causes greenhouse gases. Burning fossil fuels for heat and using certain products that contain greenhouse gases also contribute. 

Electricity Production

Generating electricity produces the largest share of greenhouse gas emissions. Around 60% of our electricity comes from burning fossil fuels - mainly coal and natural gas. Also, electric utilities rely heavily on the use of SF6. Asides from the reliance of electric utilities on this greenhouse gas, some electronics like refrigerators and air conditioners use it. 

Aside from the above-listed human activities, natural processes also contribute to the continued increase of greenhouse gases in the atmosphere. These activities, in turn, increase the atmospheric concentrations of these GHGs. Respiration and air pollution also release greenhouse gases into the atmosphere. 

What Are the Effects of Greenhouse Gas Emissions?

forest fire
Photo by Matt Palmer on Unsplash

Various greenhouse gases have enormous environmental and health effects. The greenhouse effect causes the natural warming of the earth, which results when gases in the atmosphere trap heat from the sun that could have escaped into space. The greenhouse effect is the entrapment of heat close to the earth's surface by greenhouse gases. Below are common effects of greenhouse gases:

Climate Change and Global Warming

The most significant effect of greenhouse gas accumulation and increases is climate change. Global warming is the gradual increase in the average temperature of the earth's atmosphere as more heat is trapped as a function of more greenhouse gases. 

The leading cause for these environmental issues is the increase in the volume of greenhouse gases such as carbon dioxide and methane contributed by human-made activities. Some factors affect the degree to which greenhouse gas influences global warming and climate change. These factors are: 

The Quantity of Greenhouse Gas in the Atmosphere

The abundance or concentration of greenhouse gas in the atmosphere is a major effect that influences climate change. Concentration is the amount of a particular gas in the air. The larger the emissions of these greenhouse gases, the higher their concentration in the atmosphere. The measurement of greenhouse gas concentrations is in parts per million, parts per billion, and even parts per trillion. To tackle climate change, it's necessary to begin shifting to more sustainable practices that curb these quantities.

The Duration of Greenhouse Gas in the Atmosphere

How long the gas stays in the atmosphere is another factor that affects the impact of greenhouse gases on climate change. The duration greenhouse gases remain in the atmosphere differs, ranging from a few years to thousands. 

For instance, water vapor is the most abundant greenhouse gas, but carbon dioxide has a more significant impact on climate and global warming. This happens due to its abundance in the atmosphere and its relatively long atmospheric lifetime of 300 or 1000 years. 

The Global Warming Potential (GWP)

How strongly these greenhouse gases impact the atmosphere is another factor to consider. Some gases are more effective than others at warming the planet and thickening the earth's blanket. 

Global warming is a measure of how much energy the emissions of a gas will absorb over a given period. The Global Warming Potential (GWP) for each greenhouse gas enables the comparison of the global warming impact of different gases. Gases with a higher GWP absorb more energy per pound than gases with a lower GWP. Thus, those with higher GWP contribute more to warming the earth. 

Smog and Air Pollution

Sources of smog are both natural means and manufacturing activities. Smog comes from the combination of fog and smoke. In general, smog is a result of the accumulation of more greenhouse gases, including sulfur oxides and nitrogen. 

The significant contribution to smog formation is automobile and industrial activity emissions. Agricultural fires and chemical reactions also contribute. In addition, greenhouse gases contribute to respiratory diseases from smog and air pollution. 

Depletion of Ozone Layer

The ozone layer is in the upper regions of the stratosphere. It protects the earth from harmful ultraviolet rays from the sun. A depleted ozone layer allows harmful ultraviolet rays through to the earth's surface. The primary cause of this phenomenon is the accumulation of naturally occurring yet human-contributed greenhouse gases, including chlorofluorocarbons, carbon dioxide, and methane. 

Acidification of Water Bodies

Most of the world's water bodies turn acidic due to the amount of greenhouse gas in the air. These greenhouse gases mix with rain water and then turn into acid rain. Furthermore, this rainwater carries contaminants along with it and falls into the river, streams, and lakes, causing their acidification. 

Conclusion

Greenhouse gases are gases in the earth's atmosphere that produce the greenhouse effect. They help keep the earth at a habitable temperature. However, when in excess, they are harmful to the atmospheric condition. 

It's a known fact that industrial processes are largely responsible for the emission of greenhouse gases. 

Apart from natural occurrences like volcanic eruptions, human activity increases heat-trapping gases, in turn changing the natural greenhouse effect. From fossil fuel burning, like natural gas, to agricultural and commercial activities, the world creates substantially more heat. 

Although the industrial revolution created progress, it's important to examine current activities to prevent further warming. This will also help tackle climate change.

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Pin Image Portrait What Are Greenhouse Gases?

1

IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change[Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, In press, doi:10.1017/9781009157896.

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Gerber, P.J., Steinfeld, H., Henderson, B., Mottet, A., Opio, C., Dijkman, J., Falcucci, A. & Tempio, G. Tackling climate change through livestock – A global assessment of emissions and mitigation opportunities (pdf). Food and Agriculture Organization of the United Nations (FAO), Rome.

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World Research Institute. (2018, October 4). By the Numbers: The Value of Tropical Forests in the Climate Change Equation. 

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Climate and Water Resources Case Study. Greenhouse Gases (CFCs), SOEST, University of Hawaii

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Britannica. (2022, January). Greenhouse Gas. 

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Johnson KA, Johnson DE. Methane emissions from cattle. J Anim Sci. 1995 Aug;73(8):2483-92. doi: 10.2527/1995.7382483x. PMID: 8567486.

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The United States Environmental Protection Agency. ( 2022, May 16). Overview of Greenhouse Gases.

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Saunois et al. (2020). The Global Methane Budget 2000-2017. Earth Syst. Sci. Data, 12, 1561–1623, 2020. https://doi.org/10.5194/essd-12-1561-2020

Jen’s a passionate environmentalist and sustainability expert. With a science degree from Babcock University Jen loves applying her research skills to craft editorial that connects with our global changemaker and readership audiences centered around topics including zero waste, sustainability, climate change, and biodiversity.

Elsewhere Jen’s interests include the role that future technology and data have in helping us solve some of the planet’s biggest challenges.

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