Question

One mystery in environmental science is the imbalance in the "carbon dioxide budget." Considering only human activities, scientists have estimated that 1.6 billion metric tons of \(\mathrm{CO}_{2}\) is added to the atmosphere every year because of deforestation (plants use \(\mathrm{CO}_{2},\) and fewer plants will leave more \(\mathrm{CO}_{2}\) in the atmosphere). Another 5.5 billion tons per year is put into the atmosphere because of burning fossil fuels. It is further estimated (again, considering only human activities) that the atmosphere actually takes up about 3.3 billion tons of this \(\mathrm{CO}_{2}\) per year, while the oceans take up 2 billion tons per year, leaving about 1.8 billion tons of \(\mathrm{CO}_{2}\) per year unaccounted for. Describe a mechanism by which \(\mathrm{CO}_{2}\) is removed from the atmosphere and ultimately ends up below the surface (Hint: What is the source of the fossil fuels?). [Sections \(18.1-18.3]\)

Short answer

The unaccounted 1.8 billion metric tons of CO2 per year can be explained through the process of carbon sequestration. Plants absorb CO2 through photosynthesis and convert it into organic matter. As plants and organic materials decompose, they form sediments, which are buried under sedimentary rocks, ultimately forming fossil fuels like coal, oil, and natural gas. This process removes CO2 from the atmosphere and stores it in underground deposits.

Step-by-step solution

Calculate the total carbon dioxide produced by human activities

To calculate the total CO2 production, add the CO2 production from deforestation and the CO2 production from burning fossil fuels: Total CO2 produced (metric tons/year) = CO2 from deforestation + CO2 from burning fossil fuels = 1.6 billion + 5.5 billion = 7.1 billion metric tons/year

Calculate the total CO2 absorbed by the atmosphere and oceans

To calculate the total CO2 absorbed, add the CO2 absorbed by the atmosphere and the CO2 absorbed by the oceans: Total CO2 absorbed (metric tons/year) = CO2 absorbed by the atmosphere + CO2 absorbed by the oceans = 3.3 billion + 2 billion = 5.3 billion metric tons/year

Calculate the unaccounted CO2

To calculate the unaccounted CO2, subtract the total CO2 absorbed from the total CO2 produced: Unaccounted CO2 (metric tons/year) = Total CO2 produced - Total CO2 absorbed = 7.1 billion - 5.3 billion = 1.8 billion metric tons/year

Describe a mechanism for CO2 removal from the atmosphere

One mechanism by which CO2 is removed from the atmosphere and ends up below the surface is through the process of carbon sequestration. This process involves the storage of carbon dioxide in underground geological formations. Plants, through the process of photosynthesis, absorb CO2 and convert it into organic matter. When these plants and other organic materials decompose, they form sediments, which over time are buried under sedimentary rocks, forming fossil fuels like coal, oil, and natural gas. This process effectively removes CO2 from the atmosphere and stores it in underground deposits.

Key concepts

Carbon Sequestration

Carbon sequestration is a natural or artificial process by which carbon dioxide (\(\mathrm{CO}_2\)) is captured from the atmosphere and stored for extended periods. This usually involves capturing \(\mathrm{CO}_2\) from major sources like power plants, after which it is compressed and transported to a storage site. Another way \(\mathrm{CO}_2\) is sequestered is through natural processes. When plants absorb \(\mathrm{CO}_2\) during photosynthesis, they use it to grow. Eventually, when these plants die, they decay and can become buried under layers of earth. Over millions of years, these layers can turn into fossil fuels such as coal and oil, trapping the carbon below the surface.Key mechanisms for carbon sequestration include:

• Geological sequestration: Storing \(\mathrm{CO}_2\) in underground rock formations.
• Biological sequestration: Plants drawing in carbon from the air.
• Oceanic sequestration: Oceans absorbing \(\mathrm{CO}_2\) from the atmosphere.

Photosynthesis

Photosynthesis is a critical process carried out by green plants, algae, and some bacteria. It allows these organisms to convert light energy, usually from the sun, into chemical energy stored in glucose, a sugar.This process starts when plants take in \(\mathrm{CO}_2\) from the atmosphere through their leaves and water from their roots. Using sunlight, they transform these ingredients into glucose and oxygen. The oxygen is released back into the atmosphere, while the glucose is used by the plant for energy and growth.Photosynthesis is vital for the carbon cycle because it is one of the primary ways \(\mathrm{CO}_2\) is removed from the atmosphere:

• Provides energy for plant growth.
• Releases oxygen for other organisms to breathe.
• Helps reduce \(\mathrm{CO}_2\) levels in the atmosphere.

Fossil Fuels

Fossil fuels like coal, oil, and natural gas are major sources of energy for humans. They are formed from decomposed organic materials, such as plants and animals, that were buried under layers of sediment over millions of years. The pressure and heat change these materials into fuels.When we burn fossil fuels for energy, we release \(\mathrm{CO}_2\) back into the atmosphere. This contributes significantly to the increase in greenhouse gases, which affects global climate change. Characteristics of fossil fuels include:

• Non-renewable: Take millions of years to form and are depleted with use.
• Energy-rich: Provide a high amount of energy upon combustion.
• Polluting: Release pollutants and \(\mathrm{CO}_2\) into the atmosphere.

Deforestation

Deforestation refers to the large-scale removal of trees and forests, typically to clear land for agriculture or urban development. This process has a direct impact on the carbon cycle because trees and plants use \(\mathrm{CO}_2\) for photosynthesis. When forests are cut or burned down, not only does this process release stored \(\mathrm{CO}_2\), but it also reduces the number of trees available to absorb \(\mathrm{CO}_2\) from the atmosphere. Impacts of deforestation on the environment include:

• Increased atmospheric \(\mathrm{CO}_2\): Less carbon is removed from the air.
• Loss of biodiversity: Many species lose their habitat.
• Soil erosion: The absence of trees can leave the soil unprotected.

Environmental Science

Environmental science is an interdisciplinary field that studies the relationship between humans and the environment. It integrates knowledge from various sciences, including biology, chemistry, physics, and geology, to understand environmental systems and address issues such as pollution, climate change, and conservation. This field helps us understand how human activities, like burning fossil fuels and deforestation, affect global processes, such as the carbon cycle. It also aims to develop solutions to mitigate these impacts. Key areas in environmental science include:

• Conservation: Protecting and restoring ecosystems and biodiversity.
• Sustainability: Ensuring resources are used in a way that meets current needs without depleting them for future generations.
• Pollution control: Reducing contaminants in air, water, and soil.