Carbon Cycle and Climate Study Guide

Earth Science

Human Impacts on the Earth Environment

Carbon Cycle and Climate

Study Tip

Think of some words that have “carb-” or “carbo-” in them. It is likely that these things all have carbon in them! For example, if you have a carbonated drink, it means that it has bubbles of CO₂ in it. Carbon is in a lot more places than you would think!

Abundance of Carbon

Carbon, in the form of carbohydrates, proteins, and fats, is the second most common element in our bodies.
Carbon can be found on earth in many forms including diamonds, fuels, and carbon dioxide gas.

Study Tip

Short-Term Carbon Cycling

Carbon dioxide gas is cycled in two ways.

Photosynthesis is a process that plants undergo that takes carbon dioxide and water and creates glucose (sugar), and oxygen. This is how plants generate food for themselves. This process is shown by the equation: 6CO₂+6H₂O+Energy from Sunlight→C₆H₁₂O₆+6O₂
Respiration is the reverse of photosynthesis and is the process that plants and animals undergo in order to break down the sugars in food and obtain energy. This process is shown by the equation: C₆H₁₂O₆+6O₂→6CO₂+6H₂O

This picture shows a diamond, an example of pure carbon.

Long-Term Carbon Cycling

Long-term, carbon is cycled via carbon sources and carbon sinks.

Carbon Sources: More carbon is provided than stored. They are reservoirs from which carbon can enter the environment. The mantle functions as a source.
Carbon Sinks: More carbon dioxide is absorbed than emitted. They are reservoirs for storing carbon. Living forests and oceans function as sinks.
Reservoirs are able to change between sources and sinks. The amount of time that carbon stays in a reservoir on average is the residence time in that reservoir.

Carbon Dioxide in the Atmosphere

The amount of CO₂ in the atmosphere is very low, meaning that small changes in the amount of CO₂ can have huge effects.
Through the method of measuring the composition of air bubbles in glacial ice, scientists have been able to able to determine the changes in amount of atmospheric CO₂ over time. They have determined that there has been a huge increase of the carbon dioxide in the atmosphere since the beginning of the use of fossil fuels.

Earth Science

Human Impacts on the Carbon Cycle

This landscape in Malaysia has been deforested in order to make room for growing tea.

The use of fossil fuels by humans has greatly changed the balance of the carbon cycle. Fossil fuels are natural sinks for CO₂ when they form; when they are burned, they become sources of CO₂.
The burning of propane (C₃H₈+5O₂→3CO₂+4H₂O) shows that when a hydrocarbon is burned, it adds carbon dioxide to the atmosphere. The burning of fossil fuels all over the world has added a huge amount of CO₂ to the atmosphere.
Deforestation also plays a huge role in the increase of CO₂ in the atmosphere. Trees are able to absorb CO₂ naturally, but when they are cut down or burned they lose this ability and go from a carbon sink to a carbon source.
It is important that we try to limit the amount of CO₂ in the atmosphere because carbon dioxide is a greenhouse gas. This means that CO₂ traps heat energy and warms the earth.

Concept Check

Be able to describe the processes of photosynthesis and respiration.
Be able to differentiate between a carbon source and a carbon sink.
Be able to explain how the use of fossil fuels affects the amount of carbon in the atmosphere.