What Is the Greenhouse Effect?
The greenhouse effect is a natural phenomenon that helps maintain the average temperature level of 15°C on the Earth’s surface. In this process, the thermal radiation from Earth’s surface is reabsorbed by greenhouse gases and then radiated in all directions, which provides thermal regulations for all living species on Earth. Namely, the greenhouse effect is indispensable for life because, in its absence, the average temperature would be minus 18°C.
The Earth’s atmosphere is a gaseous layer that surrounds the planet and is retained by the Earth’s gravity. The light from the Sun, invisible ultraviolet and infrared wavelengths penetrate the planetary atmosphere, and oceans and land naturally absorb approximately 70% of this solar radiation. The rest is reflected in space, but the real issue is the radiation absorbed in our atmosphere. Greenhouse gases retain the radiation in the atmosphere, thus increasing the planet’s average temperature.
While the natural greenhouse effect is essential for the Earth’s climate and all living creatures, the increased amount of greenhouse gases in the atmosphere is a global issue that affects all living species. The CO2 released from the burning of fossil fuels, over time, accumulates and creates a so-called “insulating blanket” around the Earth, which traps the Sun’s heat in the Earth’s atmosphere and ultimately increases the average temperature. In other words, the release of CO2 contributes to the current intensified greenhouse effect.
Which Gases Cause the Greenhouse Effect?
Greenhouse gases and the balance of the greenhouse effect depend on three factors: how much heat is absorbed, how much of the heat is re-radiated, and how much of it is in the Earth’s atmosphere. Gases that contribute most to the greenhouse effect are water vapor (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and ozone (O3).
The gases mentioned above have different power of absorption and re-radiation, also known as global warming potential (GWP). The greenhouse gas’s ability to trap extra heat in the atmosphere relative to carbon dioxide (CO2) is most often calculated over 100 years and is called the 100-year GWP. Interestingly, methane is 23 times more effective, and nitrous oxide is 296 times more effective than carbon dioxide. Still, there is a substantially higher amount of carbon dioxide in the Earth’s atmosphere than methane or nitrous oxide.
The greenhouse gases emitted into the atmosphere do not remain there indefinitely. For instance, the amount of carbon dioxide released into the atmosphere and the amount of carbon dioxide dissolved in the water surface of oceans are in constant equipoise because air and water mix well at the surface.
Anthropogenic Greenhouse Gases
Since the start of the Industrial Revolution, human activities have changed the environment considerably. This includes increased concentrations of greenhouse gases in the atmosphere. The primary sources of anthropogenic greenhouse gases are burning fossil fuels, agriculture and forestry, cement manufacture, and aerosol emissions.
- Burning fossil fuels
Scientists at NOAA Climate stated that carbon dioxide levels are considerably higher than in the last 800,000 years. Human activities add more carbon dioxide annually into the atmosphere than the natural processes can remove each year. For instance, in the 1960s, the global growth rate of atmospheric carbon dioxide was roughly 0.6 ± 0.1 ppm per year, and only half a century later, between 2009-18, the growth rate was 2.3 ppm per year (Blunden & Boyer, 2020). In a period of 60 years, the annual rate of increase is approximately 100 times faster than in previous natural increases, such as at the end of the last ice age 11,000-17,000 years ago.
The burning of fossil fuels has increased carbon dioxide levels from an atmospheric concentration of approximately 280 parts per million (ppm) in pre-industrial times to over 400 ppm in 2018. In other words, since the start of the Industrial Revolution, human activities have led to a 40 % increase in the atmospheric concentration of carbon dioxide. With the current rate of about 2–3 ppm/year, by the end of the 21st century, carbon dioxide concentrations are estimated to exceed 900 ppm.
Suppose this trend of substantially increased carbon dioxide emissions, methane, and other greenhouse gases continues by 2100. In that case, the average surface temperature at the global level could increase by up to 4.8°C compared to pre-industrial levels (Lindsey, 2020). To stop this temperature rise, scientists suggest projects limiting the concentrations and keeping the temperature change as low as possible, preferably below +2°C. The limitations include cuts in anthropogenic greenhouse gas emissions and extensive changes in the energy systems at global levels.
According to the new International Energy Agency (IEA) analysis, the global energy-related carbon dioxide emissions rose by 6% in 2021, to 36,3 billion tonnes (IEA, 2022). This is the highest ever level, and the main reason for it is the strong rebound of the world economy after the Covid-19 crisis, which mainly relied on coal to power the growth and demand.
- Land use
Significantly increased land use for agriculture, deforestation and other purposes are accounted for one-quarter of anthropogenic greenhouse gas emissions (IPCC, 2019). The primary sources of emissions are feed production (45 %), greenhouse gas outputs during digestion by cows (39 %), and manure decomposition (10 %). Also, the production and transport of animal products contribute to total greenhouse gas emissions. Moreover, the increased utilization of wetlands and landfill emissions lead to increased methane concentration in the atmosphere.
- Cement manufacture
Cement is the second most-consumed resource in the world, right behind water. Globally, more than 4 billion tons of material are produced every year. The process of manufacturing cement includes the heating of calcium carbonate, which results in the production of lime and carbon dioxide. As such, this industry is one of the major global emitters of carbon dioxide, emitting approximately 8 % of global carbon monoxide emissions (Lehne & Preston, 2018).
- Aerosols
The burning of fossil fuels has several side effects on the planet, including the small particles suspended in the atmosphere called aerosols. Aerosols can be released from chlorofluorocarbons (CFCs) used in refrigeration systems and halons used in fire suppression systems. Along with the aerosols produced by human activities, several natural processes, including forest fires, volcanoes, and isoprene emitted from plants produce aerosols.
While the greenhouse gases lead to increased temperatures on the Earth’s surface, aerosol pollution can counteract the warming effect. For instance, sulfate aerosols are the product of fossil fuel combustion. This aerosol reduces the amount of sunlight that reaches the Earth’s surface and thus causes a cooling effect.
Benefits of the Greenhouse Effect
While greenhouse gases contribute to global warming, at the same time, they are sustaining life on this planet. Besides regulating the temperature on the Earth’s surface, greenhouse gases offer a myriad of other benefits. Greenhouse gases block the harmful solar radiation from reaching the Earth’s surface. These gases act as a shield that makes the unwanted damaging energy reflect back into space. One of the most important greenhouse gas, ozone, absorbs the Sun’s harmful ultra-violet (UV) rays by 97-99 %. Without the ozone layer, the UV rays would penetrate the Earth’s surface, and long-term exposure to a high level of it can severely damage both animal and plant cells. The greenhouse effect also enables the planet to maintain water levels when it comes to water surfaces.
Sources:
Blunden, J. & Boyer, T. Eds. (2020). State of the climate in 2020. Bull.
Intergovernmental Panel on Climate Change. (2019). Land is a critical resource, IPCC report says. Intergovernmental Panel on Climate Change. Retrieved from: https://www.ipcc.ch/2019/08/08/land-is-a-critical-resource_srccl/.
International Energy Agency. (2022). Global CO2 emissions rebounded to their highest level in history in 2021. International Energy Agency. Retrieved from: https://www.iea.org/news/global-co2-emissions-rebounded-to-their-highest-level-in-history-in-2021.
Lehne, J. & Preston, F. (2018). Making concrete change: Innovation in low-carbon cement and concrete. Chatham House. Retrieved from: https://www.chathamhouse.org/2018/06/making-concrete-change-innovation-low-carbon-cement-and-concrete-0/about-authors.
Lindsey, R. (2020). Climate change: Atmospheric carbon dioxide. National Oceanic and Atmospheric Administration. Retrieved from: https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide.